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- V RAMA
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ܚܘܝܚܐ ܡܝܬܝܘܗܝ ܚ-- omoܐ
 
 

1. ¬ ܢ
KRISHΝΑΝ -

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A PRIMER OF EVOLUTION
V. RAMAKRISHNAN B. A., B. Sé. (Hons)

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First Edition, March 1953
SRI LAN KA PRINTING WoRKs
K. K. S. ROAD
JAFFNA
All rights reserved Price Re. 1-75

FOREW ORD
My interest in evolution has been largely in respect of its philosophical implications and applications. Whatever technical details I know were picked up incidentally in the course of my general reading. Therefore I disclaim all competence to speak with authority on the strictly scientific content of biology. But the concept of evolution has ceased to be purely a biological notion, and has invaded every realm of thought. Religion, Politics, Economics, Sociology, Anthropology, Metaphysics have all felt its impact. And all who are interested in these disciplines will do well to acquaint themselves with the germinal source of this influential doctrine.
Mr. Ramakrishnan has done a commendable job of work in assembling, within a narrow compass, the salient points of the story of Life on Earth laying bare the probable course of its movements from unicellular simplicity to multifunctional complexity. He has also at relevant points in the story drawn attention to the theoretical inferences that emerge from the story.
The author has as far as possible avoided technical jargon and 1 old a straight-forward and coherent tale that will appeal to the interested lay-man as well as to the scientific student. I am happy to record my appreciation of Mr.Ramakrishnan's effort.
4and, /Petin hanayayam .ܠܲܢ

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PREFACE
I wrote this book for two reasons. The first was that my good friend Mr. T. Isaac of the tutorial staff of Jaffna College suggested that I write this book as he thought it would help Advanced Level and other students in their examinations. The second reason was that, listening to Mr. S. H. Perinpanayagam, Principal of Kokuvil Hindu College, speak at a function last July on Darwin's contribution to world thought, I felt, that I might make a belated but more tangible expression of homage to Darwin by writing this book.
Except for the extreme examples I have chose to prove general laws, there is nothing very original in this book. Nor have I mentioned many of the exceptions” tỏ general rules, my reason being that, once a correct and useful idea is planted in a young head, the brain should be fertile enough to permit the growth of the theory of evolution in all its ramification.
My thanks are due to a number of people, in particular to Mr. Perinbanayagam who, in the midst of his heavy work, has very kindly written a foreword. Mr. M. Karthigesan, iny very modest but versatile colleague, has been of great help both at the manuscript and proof stages of the book. My old student and now my colleague Mr. K. Pathnanayagam, knowing my leisurely way of doing things, did everything except pulling my ears to make me work. And then there are my pre-medical students of last year who patiently listened to what I had to say on evolution and, by understanding the subject or pretending to do so, gave me the confidence to convert the oral word into print. To all of them, be they colleagues or students, I am deeply indebted.
To the printers, Sri Lanka Book Depot, my thanks are also due. They have done a very good job in very quick time. Jaffna Hindu College հ), kamaktisina Jaffna, 25-3-59

C O N T E N T S
CHAPTER PACE
1. Introduction 1. 2. Evolutionary ideas A 7 3. Lamarck a 4. Charles Darwin s 24 5. Hugo De Vries ... 38 6. Mechanism of Origin of Variations ... 41 7. Evidences for evolution
A. Evidence from classification s 45
B. Evidence, from Morphology and
Comparative Anatomy a s 49 C. Evidence from geographical distribution 54 D. Evidence from Palaeontology 66 E. Evidence from Embryology 4 p. 81
F. Evidence from Comparative Physiology S8 8. Man in evolution ... 92

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INTRODUCTION
Man continually tries to understand the history of his race. Two basic problems have continued to Worry him, and during the various periods of his history he has suggested expla
nations
(1) (2)
TO
to ans Wer the questions:
How did life first appear on this planet?
How did the large variety of living forms originate?
answer the first of these questions the
following suggestions have been made:
(1)
(2)
Some philosophers held that all living forms have existed as they are today eternally. They asserted that there was no beginning for these forms and there will be no end. This is the naive theory of the eternity of present conditions. Modern philosophers do not believe it very much.
The second suggestion was based on the beautiful story of Creation, given in the first book of Genesis. The same idea is expressed in the sacred books of most religions of the World. This hypothesis states
(i) that God in his infinite power created
life from non-life, and
(ii) so life arose spontaneously at the will
of God,

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Many people believe in this hypothesis even today because it leaves no lurking doubts in the mind and its completeness coloured by its religious aura makes it respectable and right.
In Europe during the middle ages this belief was backed by the might of the church. With the Inquisition functioning none dared to question this view openly. But the waning power of the church during the 18th and 19th centuries emboldened a few intellectual rebels to contest this belief.
During the middle ages it was believed that maggots arose spontaneously in rotting meat.
Franscesco Redi, an Italian scientist, 'operformed the very simple experiment of keeping rotting meat covered over by a closely woven wire-mesh. Even after a number of days no maggots appeared in the rotting meat. Consequently he showed that maggots develop from eggs laid by flies on decaying meat and do not arise de novo in the meat.
The believers in the spontaneous origin of life came back with the answer that while larger organic forms only arise from pre-existing forms, the minute microscopic forms like Protozoans 'and Bacteria do arise spontaneously in food infusions.
1. Anthony von Leewonholk, a Dutch grocer, whose hobby was grinding lenses and constructing compound microscopes, opened up the field of microbiology. He was the first to see minute Protozoans. IIe was made a Fellow of thc Royal Society, although he did not know Latin, then the language of the elite. His work is told in a very interesting manner by Paul de Kruif in his book "Microbe Hunters'.
The believers in the creation of life by God hailed the dis. covery of these minute forms round about this time as positive evidence of divine levelation, helping to strengthen their case,

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Lazarro Spallanzani, another brilliant Italian scientist, proceeded to put this assertion to the test. He left a few flasks with , meat broth in them exposed to the atmosphere. In a few days millions of minute organisms were found in the broths. Then he boiled the broths for long periods at a high temperature and before they cooled, he drew the necks of the flasks under a flame and sealed them. These sealed flasks were laid aside. After a number of days when the broths in these sealed flasks were examined, no organisms were seen. So Spallanzani stated that these microscopic organisms were present in the atmosphere in some form and, having settled on exposed food, grew and multiplied rapidly. No forms appeared in the broths of the sealed flasks because earlier boiling had killed off forms that may have been present in the broths and further contamination was prevented by the sealing of the flasks.
The believers in the spontaneous origin of life were not beaten yet. Led by the lordly Buffon and the godly Bishop Needham, they came back with the statement that foods have a life-producing substance in them, a “vegetative force,” and the continued boiling of the broths at high temperatures by Spallanzani had killed this life-forming substance. The scientist answered them by breaking the neck of one of his sealed flasks and exposing the broth to the atmosphere. In a few days microscopic organisms Were seen in plenty in the broth,
In the modern day it is generally accepted that life originates only from pre-existing life. It

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is quite true that when the earth was first formed life as we know it today could not have existed. As the surface of the earth cooled, organic forms must at some time have appeared. This appearance could well have been due to creation. In fact there is room for faith here. But very probably in the dim past some conditions existed which enabled inorganic matter to come together in a peculiar combination which showed the property of life. After all living forms can be broken into the various elements in earth. So it need not have been impossible for these elements to have qoʻime together under certain conditions to form life? That those conditions do not obtain today or that we do not know what those conditions were need not invalidate the hypothesis that animate forms first arose from inanimate matter without design. The unknown now is not necessarily unknowable. Even now there are in existence materials which form a bridge between the animate and the inanimate.o
The second basic question of the origin of different living forms is answered in a very satisfying manner by the theory of special creation. According to this theory all forms were created by an omnipotent deity in His inscrutable wisdom and it is atterly futile to enquire into the whys and wherefores of His actions. This belief is very widely held as it guarantees mental peace and
2. The position of viruses in nature seems to be anomalous. They crystallize like inanimate matter but multiply like organic forms. But viruses are known only in other systems and never in a free state. But it is quite possible that this habit may have been derived by secondary adaptation,

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conflicting factual evidences can always be explained away as the limitations of poor man trying to understand the ununderstandable.
The development of the study of the rocks with the disco very of organic forms which existed in the earlier eras of the earth, but of which there are no modern living representatives, raised doubts about the theory of special creation in the minds of some scientists. But faith was still strong and these thinkers explained away conflicting evidehces by offering a number of hypotheses.
Cuvier held that a number of catastrophies had repeatedly occurred on the earth at various places at different times. These catastrophies had destroyed all organic forms in regions where they occurred and remnants of these were left in the rock record of the earth. Cuvier stated that repopulation of these areas was by migration from other areas which may have had different types of forms created originally.
D'orbigny, another great French biologist, Was more logical. He postulated periodic Worldwide catastrophies with extinction of organic forms Repopulation according to him was due to successive creations. On this hypothesis one would be hard put to explain how some organisms have continued to exist right through the ages without suffering extinction during successive catastrophies.
3. Cuvier (1768-1832), a great French anatomist. He was the Director of Botanical Gardens in Paris. He was about the most in fluential scientist of his time.

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But
geologists are now agreed that such
catastrophies, either local or universal, did not occur in the history of the earth.
Summary:
(l)
(2)
(3)
Man is the only animal conscious of the fact that he has a history. So he strives to know how life arose first and how the variety of organic forms originated.
Nowadays it is generally accepted that life arises only from pre-existing life.
How life first arose is still an opën question. It may have been created or it " may have arisen by a peculiar combination of inanimate matter under conditions of which we know nothing.
The origin of the variety of organic forms was held to be by divine creation. Conflicting facts brought to light by geology were explained away on the basis of successive cataclysms, local or universal, with repopulation later by migration from
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EVOLUTIONARY DEAS
In the history of man a number of philosophers
have suggested that organisms have evolved' and are not created at an almighty word.
In the Greek period Empedocles (495-435 B. C.)
Democritus (460-357 B, C ) and Aristotle (384-322 B. C.) believed that new organisms arose in the following manlıuer:
1. Life has a perfecting principle in itself Which makes it consciously modify itself.
2 These modifications occur according to a set plan aimed towards attaining perfection. So change of forms appears continOusly.
3. The types of changes vary as needs vary.
4. As a result a large variety of new forms
are produced.
The term "evolution' implies the following: (a) All living forms have originated from others which existed
earlier (descent). (b) Slight structural changes accompany this descent (descent
with change). (c) There is a distinct time-scale in the order of appearance
of forms (descent with change in chronological sequence). (d) The process of change is a slow gradual one. (e) The change is towards attaining perfection of form in re
lation to the habitat. So evolution may be summed up as descent with slow chan. ges in chronological sequence aimed towards perfection in relation to habitats.

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But independent thinking became dangerous as the church became more and more powerful and after the Greek period free thought had to wait for expression almost till the beginning of the 19th century. Only then did a number of thinkers start suggesting ideas on the origin of organic forms, Buffon, Erasmus Darwin, Linnaeus, Lamarck, Charles Darwin and Alfred Russel Wallace were products of the age.
Linnaeus (1708-1788) contributed a mass of facts about living forms. His contribution to the study of biology may be summed up as folloys:
(1) He arranged the variety of organic forms in a systematic manner. This arrangement helped men to see an underlying basic unity in all the diverse forms present.
(2) He invented the system of binomial nomenclature in naming Organisms. According to this system each form is indicated by two names, a generic name followed by a specific name.
(3) He introduced uniformity in the naming of organisms by using Latin or Latinized terms. This method had the following advantages:
(a) The use of a dead language had the merit of not treading on any corns of national or linguistic vanity.
(b) This avoided the necessity for each linguistic group to coin separate names.

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(4) . He believed that life was origin illy created
s but hybridization and environmental influ. ences diversified the original creation into the large variety of living forms seen in the modern day.
Buffon (1707 - l'783) and Erasmus Darwin (1731 - 1802) held very nearly similar views on the origin of for ins. The basic tenets of their philosophy can be stated as follows:
(1) Both believed that all existing organisms
elaborated from a basic life-mass created by God.
(2) They held that in the modern day living forms arise only from other living forms.
(3) They stated that changes in the structure of organisms are due to the effect of the environment. Buffon believed that environment directly induced changes in the structure of living forms, but Erasmus Darwin held that environment only produced an internal change, which expressed itself externally as a changed body character.
(4) Both believed that there is a keen struggle
for survival almong organisms.
(5) They stated that, while they did not know the exact method by which diverse forms elaborate from the basic life mass, they
were certain that it happens purely according to natural laws."
Lamarck, Charles Darwin and Wallace stand
out as thinkers who suggested plausible methods by

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which varied organisms could have elaborated from a basic life-mass.
Summary:
(1) A number of philosophers, even during the early periods in history, stated their belief in the evolution of organisms.
(2) During the middle ages such ideas could not be expressed freely as the church frowned on them.
(3) With the power of the church waning, thinkers began to question the scriptural explanation of the origin of living forhus.
(4) Linnaeus was responsible for bringing in
orderliness in the study of biology.
(5) Buffon and Erasmus Darwin anticipated later thinkers in holding that new firms arise as a result of the influence of environment on organisms.
5. The world has been evolved, not created; it has arisen little by little from a small beginning and has increased through the activity of the elemental forces embodied in itself, and so has rather grown than suddenly come into being at an almighty word.... . . . . . . . . .....All that happens in the world depends on the forces that prevail in it and results according to law: but where these forces and their substratum, matter, come from we know
not, and here we have room for faith.' (Erasmus Darwin)
میل

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LAMARCK
Jean Baptiste Lamarck (1744 - 1829), the French naturalist, was primarily responsible for giving impetus to free thought after its enforced rest during the middle ages. During his life-time he suffered greatly as a consequence of his freethinking, and his influence on contemporary thought was very little.
* His contributions to the study of life can be stated as follows:
(1) He coined the term 'Biology to describe
the study of living forms.
(2) He classified the then known animals in a
scientific, systematic manner.
(3) He was the first to suggest a plausible method by which living forms could have diversified from a basic stock. He represented this organic continuity of living forms as a tree with a main continuous stem running from base to tip with side branches representing the relative positions of organisms."
(4) He did not believe that catastrophies as
postulated by Cuvier ever occurred.
(5) He stressed the importance of the environ
ment in moulding the characters of organisms.
6 This means that a modern form has not originated directly from
another modern form but that both have diverged from common ancestors.

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Lamarck' suggested that the large variety of living forms could have originated in the following
way :
(l)
(2)
(3)
(4)
(5)
Living forms always arise from other living forms in an orderly manner. During this descent forms become progressively adapted to conditions in their environment.
Modifications in structure are due to a need felt by the organism to fit perfectly
into its habitat.
Each such modification itself acts as a new condition and in its turn brings" on" another structural change.
Modifications in structure acquired by the organism to meet environmental needs be come emphasized if used constantly and dwindle and even disappear if not used.
Such acquired characters are transmitted to the off-spring.
. On the basis of these formulations, the origin of a new form occurs as described below:
(1)
A particular environmental condition induces the development of structural modifications in organisms. Since these develop only as a result of a need felt by the organism, they help it to live more efficiently than
7 Lamarck is a pathetic figure in the history of zoology. He had no influence on the thought of his time as he was opposed to the more influential Cuvier. Ostracized from society, he became poor and blind. Weismann's opposition to his views later almost made him a figure for ridicule But his contribution to biology is gaining greater recognition now.

፲፰
their ancestors did in this particular environment.
(2) These helpful modifications are constantly used during the life of the organisms and so get emphasized.
(3) Each generation transmits emphasized
modifications to its off-spring.
(4) If environmental conditions remain unchanged, these modifications continue to be of use in successive generations and become more and more developed.
(5) At the end of a Lumber of generations these modifications may have got so well developed that the organism may appear to be very different in structure from the ancestral form and merit the title of a new species.
New species may be formed in the reverse way also. A change in the environmental condition may make a particular structure in an organism useless. So this structure falls into disuse: As a result, it gets reduced in size. This reduced condition is transmitted in heredity. If environmental conditions remain unchanged, this structure is reduced further in successive generations and finally disappears. So at the cind of a number of generations, an organism may differ markedly from its ancestral type and may merit elevation to the rank of a new species.
The two fundamental premises of the Lamarckiam doctrine are:
(a) the effect of use and disuse on organs.

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(b) the inheritance of these characters acquired by the organism during its
Lamarckians state that the following facts support their hypothesis.
1. Cave-dwelling forms
In Austria are found a number of underground caves, some even with rivers in them. This habitat has very little food and practically no light. The animal population of these caves is poor both in numbers and variety. But the few forms that are present generally show the following characters:
(l) Their bodies are slender. (2) Most of them do not have eyes. (3) Generally they lack pigmentation. (4) The senses of touch and smell are very
highly developed.
Lamarckians explain the possession of these characteristics in the following manner:
(a) The slender body is due to poor food supply. This character is handed down in heredity so that no great demand is made on the environment by forms in successive generations. Here a character acquired in one generation is transmitted in heredity.
(b) The continued disuse of eyes in the dark environment has tended to reduce them. This reduced character is transmitted in heredity and in successive generations dwindles and disappears completely.

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Here both the basic tenets of Lamarckism, that disuse tends to reduce the size and importance of organs and that these acquired characters are transmitted in heredity, are seen,
(c) The same is true for the lack of pigmentation in them. In a habitat with plenty of light pigments help to camouflage the individual and also prevent the harmful rays of the sun injuring the body. But in the complete darkness of these underground caves disuse has eliminated these pigments in the course of a number of generations.
(d) The over-development of the senses of smell and touch is due to their constant use in a dark environment and emphasis in successive generations. This is also an instance of the inheritance of acquired characters.
(2) Dwarfing of individuals
Silk-worms reared on normal food supply grow to an optimum size but, if these are fed poorly in one generation, they become stunted in growth. More than that, in the next two or three generations also the progeny fail to attain the
8 This is one of the strongest proofs of the truth of the Lamarc. kian doctrine of the evolution of organic forms. Eyes and even pigmentation at worst can be indifferent but never dangerous, So complete disappearance of these is possible only if the reduced conditions formed as a result of disuse are transmitted in heredity, Rarwinigun, to be discussed later, does not explain this fully,

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optimum size even if normal diet is restored. The smaller size attained is most certainly due to poor food supply, a character acquired by these forms in one generation. This character seems to be handed down to the off-spring. The restoration of optimum growth after a few generations of normal feeding adds up as another proof of the effect of environmental conditions in inducing structural modifications and their transmission in heredity. (3) Inheritance of instinct
Instinct may be defined as the unreasoniig impulse shown by organisms without any thought of change or improvement in method, Nestlings are usually taught to feed and fly by their parents. When they grow into adults and start breeding, their nest - building habits run true to that of their tribe. This faculty is usually attributed to a lingering memory of their own infancy.
But a brood of ducks hatched in an incubator showed all the normal nest-building habits of their race. This can only be explained on the basis of transmission of acquired faculties in heredity.
An assessment of the Lamarckian hypothesis of evolution of organic forms.
It is doubtful if organisms consciously strive to become perfectly fitted to the conditions of their environment. If this were so, evolution of Organisms should have been a continual progress. Failures in life, found in plenty in geological history, cannot be explained on this basis. This purposiveness of life, implied in Lanarckism and made explicit later by biologists like Cope, Eimer

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and Driesh and philosophers like Bergson and Shaw, is doubted by a number of modern scientists.
The statement of Lamarckians that in ontogeny (history of an individual, life - history) continued use of an organ tends to emphasize its size and importance and continued disuse tends to reduce these, is obviously true. But how much these changes contribute to the origin of recognizable new forms depends on the degree of their existent or non-existent transmission in heredity. In fact the major criticism against Lamarck has been that his hypothesis stands or falls by the validity or inyalidity of the theory of inheritance of acquired Čharacters.
August Weismann (1834-1914) performed the oftquoted experiment of cutting off the tails of mice as soon as they were born. He continued doing this for a number of generations. He found at the end of the series that, when these mice were allowed to grow tails, their tails grew up to their usual size, not showing any visible sign of having lived without tails for a number of generations. So, Weismann said that characters acquired during the life-time of an individual are not inherited.
In fairness to Tuamarck it must be stated that this experiment means very little, except that mutilations of the body either accidentally acquired or deliberately imposed are not transmitted in heredity. But these are not true acquired characters in the Tuamarckian sense. According to Lamarck
8 Acquired characters in the Lamarckian sense are those acquired by an organism during its life-time as responses to needs in habitats for survival.
3

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18 the presence of tails in mice in their natural habitat should mean that tails are necessary and useful to these forms for survival in their habitats. The cutting off of tails by Weismann was not, a structural modification developed by the organism to meet an environmental need." The rearing of these mice in artificially constructed habitats under experimental conditions is an additional reason for dismissing as irrelevent inferences that Weismann and his followers may have drawn from this experiment.
9 : It is interesting to note that during the 19th century walen
technological knowledge leaped up after its enforced rest, the
physical sciences dealing with inanimate matter found it unchanging and obeying fixed natural laws absolutely. This rigid
order in nature made physicists subscribe to a philosophy of me.
chanical materialism. But biologists in that period, struck with
wonder at the variety of living forms and their functioning,
their perfect adaptations to different modes of life, unpredict
ability of behaviour and the apparent design or free-will in their actions, often subscribed to a philosophy of idealism.
But as study of matter progressed, it became so attenuated that all that is basic in matter is a set of electrical charges revolving round others in formations. In fact in a recent conference a Chinese scientist made matter still more ethereal by claiming that each one of these electrical charges is itself a complete system. These systems seem to be mutable as charges are apt to jump out of one system or jump into another. These jumps are unpredictable and so the physical sciences have come the full cycle and become idealistic. The fact that matter at least in large masses still obeys Newtonian laws helps one to keep one's sanity.
But biologists have completed the reverse cycle. Living material has been analysed part by part and broken into the very elements themselves. Pavlov with his conditioned reflexes and the behaviourist school of psychologists have reduced wise man himself to a bundle of reflexes requiring neither design nor free-will for effective functioning. And some even assert that organisms are verily nothing more than a fairly complex machine. And so quite a few of them subscribe to a philosophy of materialism in some form.

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Weismann's work was done later than that of Lamarck. By his time the cell-contents and their behaviour had been worked out to a certain extent. On the basis of the then known facts of cytology Weismann formulated his famous thesis of the purity and continuity of the germ-plasm. This theory, if true, is a telling argument against that of the inheritance of acquired characters. The germ-plasm theory states :
(a) that in organisms reproducing by the sexual method two sex-cells or game tes fuse together to form the Zygote, the start of the next generation,
(b) since only gametes enter into the formation of the next generation, any character expressed in that generation must be represented in the gametes,
(c) that in multicellular forms the zygote elaborates both into the vegetative (soma) and the germinal (germ) parts,
(d) at death only the soma dies and the germ is continued in the next generation through the gametes,
(e) the germ-plasm is kept completely insulated from soma although it exists within it, and so any somatic modification acquired by an individual during its life-time can never induce a change in the constitution of the germ-plasm,
(f) and so for any structural modification to be transmitted in heredity it minst have, a germinal basis. If the germ-cells cannot be influenced by the somatic modifications

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inheritance of acquired characters cannot OCC.
So, Weismann stated that Lamarckism cannot account for the origin of species.
There is quite a lot of truth in Weismann's theory of the germ-plasm. There is no doubt that a fair amount of insulation of the germ-plasm from somatic influences exists. For example, pathogenic diseases of the soma are never transmitted to the offspring through the gametes."
But it is doubtful if a complete insulation of one part of an organic whole from another' is possible. The germ-cells are living cells and the cytoplasm in them constantly exchanges materials with other cells. The nuclei of the germ-cell in turn exchange materials with the cytoplasm that surrounds them. So the influence of the cytoplasm on the nucleus cannot be ruled out. Since nucleus and cytoplasm live together in a state of dynamic equilibrium, each must be influencing the other considerably.
So, while acquired modifications in the crude sense of mutilations may not be transmitted in heredity, there is not sufficient reason to suppose that germ-plasm can never be changed by environmental influences. It is now known that a number of external factors like Colchicine and
10. Young ones developing in the womb never get the pathogenic diseases of the parent transmitted to them in heredity. Even syphilis, which sometimes makes human children to be born blind, is not transmitted in heredity but affects the foetus as it descends through the vagina (congenital). But the debility of the parents and the environment into which the young are born may make them susceptible to infection again. Nature is relatively clean until nurture conta minates it.

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X-rays change the nuclear complexes of germcells and that these changed conditions breed true. Even in nature such sudden changes in nuclear constitution occur quite often.
After all, characters which distinguish organisms from one another must have been acquired at some stage and these must have been transmitted in heredity if the fact of evolution (gradual descent with change) is granted. And to deny any role to the environment in influencing organisms that live in it would be a very dogmatic assertion not Warranted by known facts in biology.
In the modern day Lamarck has been resuscitated to a small extent. Followers of Michurin in Russia assert that even vegetative hybridization changes the basic constitution of both stock and Scion.
This swing towards attributing some importance to nurture is all to the good of the human race. For long, due to the influence of Weismann, organisms were studied as if they lived in a vacuum. The realization that there is a dynamic equilibrium between the individual and the environment, each continuously interacting on the other and neither continuing to remain the same as a result of this interaction, is all to the benefit of man who can use this knowledge for the materi
all prosperity and social progress of his race.
Summary:
1. The major contributions of Lamarck to
the study of biology lie in
(a) his systematization of organic forms,

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(b) (c)
3.
his belief in the evolution of such forms, his foctassing of attention on the interrelationship between organisms and their habitats.
He formulated a method by which existing organic forms could have evolved from a few ancestral types.
The basic tenets of his hypothesis on the origin of forms are
(a) There is an inherent urge in life.p. to attune itself more and more to its habitat.
(b) Structures develop in organisms to meet particular needs of the environment,
(c) These structures increase in size and complexity if they are constantly used and get reduced and even disappear if they are not used.
d) These acquired characters are transmitted in heredity in the forms they exist.
Lamarckians adduce the following as evidence of the truth of their doctrine:
(a) The attenuated body, absence of eyes and pigmentation and the over-development of the senses of touch and smell can be explained on the basis of the effect of use and disuse on organs and their transmission in heredity.

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(b) Instinct in animals can be explained only on the basis that acquired characters are inherited.
(c) Pathologists constantly seeing the wonderful plasticity of tissues assert that there is a purposiveness in life enabling it to react to the needs of its environment.
Weismann's theory of the purity of the germ-plasm raised the question whether characters acquired in ontogeny could ever be inherited.
Modern biologists hold that any organism works as a whole and the effect of the environment cannot be ruled out completely.
Lamarckism, in a slightly modified form, may influence thought for some time.

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4.
CHARLES DARWIN
The contributions of Charles Darwin (18091882) to the study of organic forms' are listed below.
(1) He collected a mass of facts on the structure, habits and habitats of a very large number of organisms. He did this mainly during his six-year voyage round the World in the scientific survey ship Beagle'. (2) He explained how in all the apparent - diversity of living forms a basic unity
can be recognized.
(3) . He offered a plausible explanation of how a few basic stocks could have diversified into the multitude of organic forms extant.
His study of organic forms during his Voyage round the world made him realise that no two forms are exactly alike. However compact and uniform a group may appear to be, slight differences or variations always exist in them. But these differences are so minute (slow) that they may not be recognized at all. According to him the term species does not indicate a group of organisms all
11. Charles Darwin and Abraham Lincoln were both born on the same day, 12th February 1809. One emancipated human minds from the shackles of slavery to tradition, and the other emancipated human bodies......... from physical bondage.' Charles Darwin served as the naturalist on the survey ship "Beagle' between the years 1831-1836. He published the story of this voyage in "A naturalist's voyage round the world.''

25
of which have exactly the same characters but only stands for the average of the group. The slight variations present in these forms revolve round a mean which is stated as the general characters of a species. He said that the origin of these variations is purely chancy and since they revolve round a mean are also fluctuating.' He noticed that a number of these variations are heritable.
Darwin knew that living forms are potentially capable of producing a very large number of offspring." This capacity can be shown by citing a few illustrations.
(a) An oyster usually lays about 20,000 eggs. If all these eggs develop to maturity and in turn breed, the heap of shells produced would in four generations be eight times the size of the earth.
(b) Professor Woodruff has reared over 9.000 generations of Paramoecium. This Protozoan
1. If 1001 boys ranging in height between 5 ft and 53 ft (ho twό boys being of exactly the same height) are stood in a row, the middle boy of the series will be 525 ft. Any two adjacent boys if taken out of the row will appear almost identical in height because the difference between them will be so very little. But if the two boys at the two ends of the row are taken out and stood side by side, they will appear very different in height. But in a row all of them will be seen to approximate to the mean of the group.
13. Darwin was influenced in his ideas to a great extent by the work of Malthus on 'Population,' which he read in 1838. Malthus stated that while increase in numbers of organisms can occur in geometric proportion, food supply at best increases very slowly. So there is bound to be a struggle to keep populations down, This is probably true of all forms except man who has under stood his history and so can mould his evolution, - - -

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divides thrice in two days. If all the protoplasm produced in all these generations had survived and continued to reproduce, the mass of protoplasm produced would have exceeded the size of the known universe and would be extending into space all round with the velocity of light.
But in spite of this potential capacity for increase in numbers, the average population of a group is relatively constant or at best increases at a slow rate. So very obviously the majority of forms never attain maturity but die in infancy.
Darwin believed that the destruction of such large numbers occurs Owing to an intense struggle for existence. Struggles for food and mate and natural calamities account for the destruction of very large numbers.
This struggle is most severe between members of the same group as all their needs are similar. The struggle between different groups of organisms for survival is almost equally severe as all organisms depend on other organisms for their food. Natural calamities like drought, floods, volcanic eruptions and land subsidences also account for the loss of quite a few forms.
The apparent effect of this struggle is a balance among the organisms living in a habitat. This prevents the abnormal increase of any one group. The intervention of man in this scheme almost always disturbs this balance and often the results are not to the benefit of man himself. A few examples of the balance of organisms in nature

and the
27
effect of the intervention of man are
given below.
(a)
(b)
(c)
(d)
In Australia Prickly Pear (Opuntia sp.) is an indigenous plant, but its population never increases to the extent of making it a pest as it has natural enemies to keep it in check. This plant was introduced into India as a cheap effective hedge plant In the absence of natural enemies this plant multiplied rapidly and soon invaded the fields. Later, its natural enemy, the Cochineal insect was introduced to check the spread of the prickly pear. This it did, but in the absence of its natural enemies, it itself multiplied rapidly and started feeding on the cash crops and in turn its parasites had to be introduced to keep it in check.
Rabbits were introduced into Australia by man. In Australia, there are no indigenous Carnivores to keep rabbits from multiplying rapidly. Now they have become a pest,
The potato beetle normally feeds on the poisonous night-shade (Belladonna). There was nature's balance so that neither increased very much. But when the potato, a close relative of the night-shade was introduced into America, the extra food supply made the beetles increase in number and they soon became a pest migrating far and wide and causing great havoc.
The nice inter-dependence of organisms in a habitat is clearly illustrated by the

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following example described by Darwin. Red Clover, a small weed, is good fodder 'for cattle. So if more clover is grown there will be more beef. Clover is pollinated by bumble-bees. Field mice feed on bumblebees and domestic cats feed on field mice. i So more cats mean less mice, more bumblebees, more clover, more cattle and more beef. Huxley's addition to the two ends of this series makes it interesting. More beef means stronger men to fight for England and cats are reared mainly by aged spinsters. So aged spinsters are, by a long process of balance, finally responsible for the production of strong men!
- - In this struggle for existence a very large number of forms die off and only very few survive. But what makes these forms survive?
Darwin answered this question by stating that only forms fitted to live in relation to their environment survive. But this only raises another question. What makes them the fittest?
And it is in his answer to this question that Darwin's major contribution to evolutionary thought lies. He stated that the forms fittest to survive are those having adaptations a shade better for successful living in an environment. These are automatically selected by nature for survival. Others being unequal to live in this environment in competition with the fittest forms are automatically eliminated in the struggle for existence. This survival of forms with variations better suited

29
than others for life in a habitat he termed Natural Selection.'" . -
species arose in the following way:
1.
According to the theory of natural selection
Slow, continuous, chancy variations exist in the members of any group. These variations are never abrupt but fluctuate round the mean set of characters of the group.
Some of these chancy variations may give a better chance for survival in a particular environment than others. Those forms with these fortunate variations survive to maturity while others die off in the struggle for existence,
These variations are inherited by the off-spring.
The characters of the off-spring of these surviving forms in turn show variations but these vary round the mean of their parental characters,
If the environmental conditions continue to be the same in this generation also those with useful variations better developed survive to maturity while others die off in the struggle for existence.
14.
The hypothesis of natural selection is jointly attributed to Charles Darwin and Alfred Russel Wallace. Darwin, on the huge mass of facts he had collected, set the theory down in broad outline and sent it to Sir Joseph Hooker in 1856. But in 1858 he received from Wallace, a young naturalist living in the East Indies, the very same hypothesis he had sent to Hooker. Strangely enough Wallace also arrived at these conclusions after reading Malthus. Darwin, a born aristocrat who was very shy and chivalrous, wanted to give the entire credit to Wallace. And not to be outdone the equally chivalrous Wallace wanted to resign all credit to Darwin. Finally both papers were read before the Linnaean Society on July 1st 1858. Darwin's magnum opus “The origin çjf species' appeared a year later (1859).

Page 21
6. Such selection of the best fitted forms for survival continues to operate in successive generations and after a long period the forms produced may differ markedly in characters from the ancestral stock and may merit elevation to the rank of a species.
7. Several variations are acted upon by nature at the same time and environmental conditions also vary sufficiently. Hence the production of a large number of species from a few basic ancestral types is not surprising.
Natural selection then continues to select the fittest in each generation for survival and eliminates the unfit. So in course of time, organisms come to show almost perfect adaptations for successful living in their environments, Visibly no unadapted forms are seen in any environment. It is this perfect correlation between organism and the environment that made some people postulate evolution as a continuously progressive movement. But it must be remembered that what we see are the successes in the struggle for existence. The failures of which there are so many are not seen in the living condition.
The hypothetical example given below illustrates how natural selection operates to produce new species. l. Let us assume that a particular parent stock in a localized habitat had claws ranging round a mean length of 0. 1''. This stock survived to maturity and produced off-spring.
2. These off-spring will have among them slight variations in claw length. Some may have

4.
31
claws slightly longer than those of their parents and others slightly shorter ones. If survival in this habitat is easier with longer claws, then those with the chancy variations of slightly longer claws than others survive to maturity while others from the same parental stock die off. (Some of these may have reached different habitats where shorter claws may be advantageous for survival. Here those forms with longer claws will be eliminated.) These variations are transmitted in heredity.
The progeny of these surviving forms in turn show variations in claw length among
themselves but these variations fluctuate round the mean of their parents, whose variations had already been proved to be advantageous for survival in this environment. Selection of forms with slightly longer claws than others operates again and again in successive generations. If environmental conditions continue to remain unchanged, at the end of a number of generations the surviving forms may have claws l' long,' which is a very long way off from the ancestral mean of 0, 1'. This structural difference may make them appear very different and these two may be termed different species'
5
16.
No apology is made for the farcical example as the aim is only to explain in broad outline how selection operates. The illustration is most certainly not a factual one.
It must be remembered that all classifications are man
made. The more scientific the basis the more will it approxi
mate to the truth of what happened in evolution. Since evolu
tion implies constant change, classification into distinct groups
is just a useful aid for studying living forms. It does not re
present any rigid compartmentalization in life, Species like every
thing else have no fixity,

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Environmental conditions are very varied. Even these are constantly changing. So variations advantageous for survival may be many. Also a large number of variations in the same organisms are being selected at the same time. So, from a basic stock diversification into the large variety of forms seen is something that is not beyond belief.
Nature selects the fittest among many for survival. So in course of time organisms in any environment come to show perfect adaptations to their habitats. These adaptations must stop at she most advantageous condition for survival. Overspecialization of any character is an impossibility if natural selection is true, for selection cannot operate beyond the point of greatest usefulness. If a certain structure once useful becomes dangerous due to changes in environmental conditions, selec. tion operates to eliminate this structure in succeeding generations.
So the perfect integration of structures of -organisms to environmental conditions is not due to purposive, directed, progressive effort of organisms to make themselves more and more fitted for survival in particular habitats, but due to nature automatically selecting the fittest forms to survive in the struggle for existence, that is, those With advantageous, random or chancy variations that exist within any closely knit group of organisms.
Species are not fixed and immutable. The members of a species differ among themselves. The
importance of these minute variations is often missed because they are so small in relation to

33
the relatively long time required for effective recognizable structural changes to be evolved by natural selection.
- It must be remembered that Darwin implicitly accepted the theory of the inheritance of acquired characters. The occurrence of a variation, while chancy is an acquired character. And natural selection can explain the origin of species only if these variations are heritable.
An assessment of the Darwinian factor of natural
selection in the origin of species
1. According to Darwin the basic materials from
which nature selects the fittest to survive are the slow,' continuous, random variations occurring naturally within a closely knit group of organisms. But this slow process cannot explain the origin of elaborate mimicry shown by a number of organisms, both protective and aggressive. If mimicry is to be of use for survival it must be complete. Slow changes
17. Slow, because the differences are very little. Continuous, be cause these variatious in any large group of organisms tend to deviate from the mean in slow steps. Random, or chancy, be cause there is neither design nor free-will in their origin. These variations are also said to be fluctuating as they revolve round a mean, some being more developed and others less developed than the average. They may, because of the fortuitousness of their occurrence be either fortunate or unfortunate depending on whether selection finds them fit or unfit for survival. 18. For example, the leaf-insect, mimicking the green leaf on which it stays, does it even to simulation of venation and leaf-injuries. It must have developed this condition fully for it to have been of any use. For a slow change to green-ness in unrecognizable doses could have had no selection value. This objection may be answered by stating that in course of time both the insect and the plant have evolved along parallel lines by slow degrees

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84
9.
towards this condition could not have had any selection value.
Study of rock strata seems to tell us of forms which became extinct due to over-specialization'
of structures. For example, the enormous antlers of the extinct Irish deer must have weighed very much more than its entire skeleton and must have been more a hindrance than help in survival. This elaboration of structures beyond the point of greatest usefulness cannot be explained by the bypothesis of natural selection as natural selection cannot operate beyond the point of greatest usefulness,
Natural selection can account for the development or degeneracy of organs. But it cannot explain their total disappearance. If a particular structure is dangerous for survival, selection will operate to reduce its size. But if the organ is neither useful nor dangerous, selection cannot operate on this organ. For example, in the cave forms described earlier, the over-development of the senses of touch and smell can be explained on the basis of natural selection. But this cannot explain the complete loss of eyes. Eyes can never
Very probably these were not over-specializations at all, do not know sufficiently well all the environmental conditions then extant. Extinction of these forms may have been due to natural calamities. The argument that tends to transpose present day conditions to the past and the tendency to judge forms and functions in relation to these must be avoided. This is, in fact the greatest danger in discussing evolution of organic forms, or for that matter any subject that requires logical analysis
 
 
 

85
be dangerous. At worst they may be indifferent and hence will have no selection value. The Lamarckian hypothesis of reduction and elimination of organs as a result of disuse explains this loss better than the theory of natural selection.
Both Lamarck and Darwin have suggested
plausible methods by which species could have diversified from common ancestral stocks. These two held the following views in common:
Both belie ved in the basic unity of life. They believed that organisms arise only from other organisms. Both held that the term species does not indicate absolute uniformity of characters. The usual statements of specific characters for a group are only expressions of the mean of the characters of a group. Both believed that change is universal in organisms.'"
Both believed that organisms inter-act with the conditions of their environment.
Both held, Lamarck explicitly and Darwin implicitly, that characters acquired by organisms in one generation are transmitted in heredity.
Both believed that the diversification of forms from basic ancestral stocks is due to a slow process of evolution.
The major differences between their view
points are:
20. With purpose according to Lamarck and at random according to Darwin.

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36
1.
LAMARCK Structural modifications arise as a result ef an
inherent property of life
to make itself more and more perfect to live successfully in particular habitats i. e., there is a purposive and directional line in the development of structures.
Structures developed to meet environmental needs tend to be emphasized if used constantly and reduced if not used. These conditions are passed down in heredity ånd so the final line of evolution of forms should
be straight. Failures can
not OCCur.
Lamarck postulated a method, for what it was worth, by which structu
ral changes arise in orga
nisms.
1.
DARWTIN
In any closely knit group of organisms minute variations of characters exist among its members. The origin of these slow fluctuating variations is purely due to chance and not caused by external influences. There is no conscious effort on the part of organisms to develop structures to meet particular environmental needs. Hence evolution of forms is not purposive.
Variations are mostly heritable. But it is not a case of useful variations getting emphasized and useless ones getting reduced, but nature
- in each generation selecting
forms with advantageous variations better developed than in others. Here also
the final line of evolution may appear to be straight and progressive. But this is so only because failures in the struggle for existence are not seen as surviving forms.
The origin of the basic material of Darwinian selection, variations, was not explained by Darwin. Modern geneticists have repaired this deficiency to Some extent.

87
Summary:
1.
2.
Darwin recognized the universal existence of minute fluctuating variations in organisms.
He knew of the great potential fecundity of organisms.
He explained the relative constancy of number in population as due to an intense struggle for existence.
He suggested that in this struggle only forms with advantageous variations survive as they are more fitted than others to live in their environment.
Since this selection operates successively in each generation, the mean of characters at the end of a series may be very far from that of the ancestral stock and so new species are formed.
Darwin implicitly accepted the theory of the inheritance of these chance variations.
Darwinism may not fully account for the development of all organisms as it may find diffi. culty in explaining the origin of mimicry or the disappearance of useless organs. Lamarck and Darwin held a number of views in common regarding origin of species.

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5
HUGO DE VRES
Hugo de Vries (1848-1935) the Dutch botanist has two claims to fame. In 1900 along with Correns and Tshermak he rediscovered Mendel's laws on hybridization and he suggested that the origin of species is not due to natural selection of slow continuous variations but to sudden jumps in the average of the characters when reproduction occurs. He called these sudden jumps discontinuous variations or mutations.
He objected to the Darwinian natural selection being the cause of origin of species as he felt that the time required by this method to produce the large varieties of forms present was very long and the earth has not had such a sufficiently long history.
He found in a field of evening primroses (Oenothera, lamarckiana) a few forms which were very much taller and had larger leaves than the others whose characters varied round the mean of the group. There was no doubt that these plants had originated from the ordinary forms of Oenothera. These larger forms bred true to their new set of characters. -
De Vries called these forms Mutants or changed rorms. These forms varied from the parental stock adically, i.e., the variations were sudden jumps or discontinuous ones. These mutants showed among themselves minute continuous fluctuating variations.

39
De Vries believed that these sudden jumps off the parental mean have been primarily responsible for the origin of new species. He likened the history of a race of organisms to the life-history Öf an individual. Just as an individual in its lifehistory shows a number of stages in development, like the embryonic, adolescent, adult and senile periods, a race also shows various stages like infancy, adolescence, adult and racial old age. An individual reproduces most actively in its adult stage. Likewise, a race during the peak of its development suddenly produces a large number of mutants and evolution of new forms occurs very rapidly during this period.
Darwin was also aware of such sudden jumps, but he dismissed them as 'sports' or freaks. He did not attach any importance to these forms in the origin of species,
There is no denying that these mutations which breed true have a role in the origin of new forms. But selection can also be operating on slow continuous variations and both may contribute to the development of the variety of species. In fact some biologists feel that the earth has had a sufficiently long history to make possible the variety of forms by Darwinian selection of minute random variations.
De Vries only suggested that the origin of new forms is due to sudden jumps in one generation. He did not deny natural selection as such but only its being the sole cause of origin of new forms Actually among these mutants selection does operate

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40
to eliminate the unfit and make the fit survive for the origin of his mutations is as random as Darwin's slow continuous variations.

es
MECHANISM OF ORIGIN OF WARIATIONS
Darwin recognized variations but he did not explain the method by which they originate. This was done only much later when the structure and behaviour of protoplasm was studied in detail, for the understanding of the nethod involves an understanding of the behaviour of the nucleus during celldivision both normal and in the formation of gametes and also during the union of gametes to form new individuals.
Chromosomes, thin thread-like structures appearing within the nucleus just before its division are mainly responsible for the transmission of characters in heredity. Chromosomes seem to possess certain factors or genes which are responsible for the external expression of body characters. These chromosomes come together in close synapsis during the prophase of the first maturation division (reduction division). During this synapsis genes placed in one chromosome may get displaced on to its fellow. The chances of the genes getting displaced are greater if they are placed further apart on a chromosome than if they are very near each other. When the homologous pairs of chromosomes segregate in the diplotene stage the gene complex of a chromosome may have changed slightly from what entered in synapsis. When gametes come together during fertilization, owing to independent assortment of chromosomes new combinations of characters may be seen in the offspring. There is no need to wonder that offspring differ slightly from the parent stock and ащопа

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themselves. On the basis of our knowledge of cytology it should be very surprising if all of them are exactly alike.
But such variations are essentially recombinations of what are already present and although external expression of body characters is conditioned not only by the presence of genes but by their relative positions and other chemical influences, still they cannot be very much off the mean of the parent stock,
The study of the laws of heredity during the early decades of this century seemed to vindicate completely the Weismannian contention of the purity of the germ plasm. It proved that external expression of characters has a nuclear origin and that nuclei are not affected by environmental influences.
Neo-Darwinists, trying to reconcile Darwin's implicit acceptance of the inheritance of acquired characters (variations) and Weismann's view of the insulation and consequent purity of the germplasm, explained the slow variations as due to pure chance nuclear rearrangements during the formation of gametes and during fertilization. They ridiculed the Lamarckian idea of characters arising in response to specific needs of the environment, their emphasis or reduction in ontogeny as a result of use or disuse and their transmission in heredity. According to them descent with change occurs purely due to chance and while Darwin was right in believing that variations are heritable, those variations are the ones occurring in the germinal complex at random and are not to be equated

43
with the acquired characters in the Lamarckian sense which are somatic modifications arising out of a need in the environment and transmitted in heredity.
Neo-Lamarckians discard the view of the acquisition of somatic characters in the crude method of modifications occurring to meet an environmental need. But they are convinced that an organism lives as a whole and complete insulation of one part from another is impossible. In fact they doubt if the role of the nucleus in heredity is absolute. They believe cytoplasm, the basic environment for nuclei, has an equally important role to play and changes in the cytoplasm do affect the nuclei, So modifications in the nuclear complex do not occur just at random but as a result of cytoplasmic influences. And the Lamarckian view that changes are induced and that these are heritable is right at least in a very diluted form.
It is now well known that polyploidy can be induced in cells. In fact the mutations of De Vries are now known to be polyploids. The characters produced by the changed chromosomal complex breed true.
So, the natural constitution and behaviour of nuclear material is the basis for the appearance of variations. In each generation nurture may make them appear to be slightly different from what nature endowed them with, but nurture never supercedes nature completely.
The origin of heritable variations on which selection operates may be summed up as follows:

Page 28
The slow continuous fluctuating variations are probably due to gene mutations occurring during the prophases of the meiotic division and the combination of chromosomes during random mating of gametes. .
The external expression of a character depends not only on the presence of the factor or gene responsible for that character but to its posi tion in relation to other genes and to certain other chemical influences. So offspring must be expected to differ slightly from the parents,
The occurrence of these slow variations is chancy as displacements of genes are not predictable.
Sometimes owing to causes not yet fully understood sudden changes in chromosomal number occur and these changed conditions breed true.
These radical changes are the causes of discontinuous variations and quite a few of these can be induced artificially. So very probably when they occur in nature also they are caused by external influences, as it is difficult to believe that one part of an organic whole can be kept completely insulated from others especially when there is a lot of interchange of materials between them.

フ
EVIDENCES FOR EVOLUTION
Evolution of organisms is a fact. The large mass of evidence offered by practically every branch of study in biology supports the postulate that all organic forms descended from pre-existing ones with change.
A
Evidence from Classification
Throughout his history man has tried his hand at arranging in groups the variety of organisms around him. He did this taking into account their similarities and differences in form and structure. Some of the earlier attempts at such grouping may now appear to us wrong and even farcical but they must be understood as brilliant attempts in relation to the very limited knowledge the scientists of those eras had of the structure, physiology and ecological adaptations. The earlier attempts at classification such as the one that lumped together all forms with superficial radial symmetry like Coelenterates and Echinoderms in the group Radiata and the acoelomate Helminth worms with the complex coelomate Annelidsunder the group Vermes should be understood in the context of the limited knowledge of anatomy scientists then had.
Our attempts at classification, with our greater knowledge of biological facts, are more orderly. In the modern day classification takes into account form, structure, function, environmental adaptations, development and racial history of organisms.

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It is possible to arrange all known animals (taking into account all factors stated in the last paragraph) in a slowly ascending series of complexity in structure. Protozoans with their entire body made up of just a speck of protoplasm through several levels of metazoan organization to complex insects or back-boned animals form a neat series.
This arrangement shows a series of graded steps from the simple to the complex. The idea behind this arrangement is not to prove that a complex form arose directly from a simpler form arranged just below it or to find missing links to connect existing groups, but only to make possible a recognition of common ancestry and a basic unity of organisms underlying all the diversity so apparent. さ
It must be emphasized that the continuity we aim at seeing is that of forms least specialized on ecological grounds. Even within the most compact group that could be arranged by this effort at classification, radical differences may
exist, some forms so highly specialized for life in a particular habitat that they cannot function as
starting points of new organisms. All that can be said is that if the least specialized of forms are arranged in a series they form a fairly continuous series which could be connected easily with some little imagination not completely unsubstantiated by biological facts. This classification does not and cannot disprove entirely the thesis of the divine origin of organisms, as there is nothing to prevent the omnipotent God from producing this apparent continuity of graded sequence. It is,

(47
however, possible to believe that these graded steps are indicative of the emergence of complex forms from simpler ones.
An additional support that classification, manmade no doubt as all classifications are, is that the position of certain anomalous forms in the natural sequence can best be explained on the basis that organisms have evolved and were not created. One such form is Peripatus. This type shows a number of Annelidan features and a number of Arthropodan characters. Peripatus has the follow. ing "characters in common with Annelids:
” (i) eyes, (ii) segmental nephridia, (iii) ciliated
reproductive ducts, (iv) food tube.
It has the following features in common with Arthropods:
(i) appendages modified to form jaws, (ii) haemocoelic body cavity, (iii) a dorsal ostiate heart, (iv) coelom confined to small spaces round the nephridia and gonads.
While it would be wrong to assume on the basis of the presence of characters of both groups in this form that modern Arthropods originated from Annelids through Peripatus, very probably both Annelids and Arthropods have evolved from a common ancestor through development of some form like Peripatus.
It must be remembered that organisms in their adult stage show structural adaptation to the habitats they live in. Even very closely related forms may show differences in structure to suit modes of life. But young developmental stages are

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least specialized. If the larval forms of a number of groups are arranged side by side, they show a nice graded sequence of increasing complexity
The Ctenophores, some · Helminth larvae, the Trochophore of some marine Annelids, the Welliger larvae of some Molluscs, the Bipinnaria of starfishes and the Torna,ria, larvae of Balanoglossus form a fairly neat ascending series. This adds up as another evidence for the correctness of our classification of forms based - on a recognition, of underlying unity with diversity attained by a process of evolution,
Summary:
1. All classifications are man-made. The nearness of any system to truth will depend on our factual knowledge of biology.
2. It is possible to arrange all living forms in
an ascending series of complexity.
3. This does not indicate that modern forms have originated from other modern forms occurring just below them in the sequence but only suggests that both may have had a commo ancestry.
4. Structural complexity of the adult forms may often be complicated by secondary adaptations to environmental conditions and modes of life. But larvae are less specialized and the basic correctness of the modern systems of classifi. cations is borne out by the fact that these larvae also can be arranged in a graded sequence of complexity,

49
5. The search for the missing links connecting groups is wrong as all modern forms actually represent ends of lines and as such no single form could be said to be a missing link.
6. While special creation also may give rise to these effects it is very probable that forms evolved.
B
Evidence from Morphology and Comparative Anatomy
The structure and arrangement of organ systems in organisms show a graded sequence from the simple to the complex. In a compact group like the vertebrates organ systems seem to be constructed on a basic plan, with secondary differences due to special adaptations. This means that these organs very probably have a common origin. Such organs are said to be Homologous.'
In the adults a set of homologous organs may perform the same function or they may not. Functional similarity in the adult state is known as Analogy. These two terms can be explained by a few illustrations.
1. The wing of a bird, the fore-limbs of the toad and the flipper of the whale are homologous organs. They are all modified fore-limbs. All of them follow the typical pentadactyle plan and have very nearly identical skeletal parts. But in the adults, the wing of a bird is adapted for an aerial habit, the limb of a toad
for a terrestrial habit and the flipper of th
2 Homology only indicates common origin and analogy only indicates
functional similarity.

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whale for an aquatic habit. All these have a common Origin and hence they are said to be homologous.
2. The wing of a bird and the wing of an insect perform the same function. These two are said to be analogous organs. But their origins are quite different. The wing of a bird is a modified fore-limb with endoskeletal structures while the wing of an insect is essentially a pulledout portion of the body-wall.
3. The flipper of a turtle and that of a whale are homologous for they are both modified pentadactyle limbs. They are also analogous in that both perform the same function.
The presence of homologous organs in a number of animals indicates evolution of forms by descent implying thereby common ancestry for a number of forms. For example all terrestrial vertebrates with limbs show the same general pattern of arrangement of bones in the limbs. In fact this basic unity in structure extends even to the arrangement of muscles round the bones. It is a little difficult to see why special creation should retain the basic pattern of the pentadactyle limb even with its musculature, all of which are nonfunctional in the flipper of the whale. The presence of this pattern of arrangement and the non-funct. ional character of structures are probably due to a descent from forms which used these structures but, with change in habits forced on by changes in habitats, these structures may have lost their usefulness.

51
A comparative study of organ systems in vertebrates shows a graded series of increase in complexity furnishing another evidence of the fact of evolution (descent with change). The differences that may be seen are often explainable on the basis of adaptations for life in particular habitats.
In the blood-vascular system, for example, the simplest condition of arrangement of aortic arches is seen in some fishes. This can be shown to give rip to the conditions present in birds and mammals by a series of graded steps. The theory of special creation of organisms would have us believe that these beautifully graded steps are unconnected. Even in the history of development of one form like the modern amphibian, the frog, the blood vascular system develops in a series of gradual steps from that characteristic of a purely aquatic form through a condition suited for an amphibious life to the condition found in the adult terrestrial form. If this can happen during the life-history of one animal it could also have happened in the larger general history of living forms.
Biologists believe, on the basis of a sufficient mass of evidence, that all modern forms have diversified from ancient marine forms. A terrestrial environment is a rather hazardous one for life. In spite of its hazards, forms pressed out of aquatic habitats may have adopted the terrestrial habitat as being the best of the bad bargains available. This transition very probably occurred along steps similar to what occurs in the life-history of a
rog.

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52.
It may still not be impossible for die-hards to assert that the very orderliness of these graded steps is indicative of the hand of an architect. But overwhelming circumstantial evidence points to an evolutionary origin of organisms. The study of comparative anatomy contributes its mite to it.
The presence of vestigial organs offer along with other evidences fairly substantive proof of the fact of evolution of organisms by descent. The presence of functional organs can be explained on the basis of creations to meet certain needs, But a number of completely useless organs are found in a number of animals like the terrestrial vertebrates. The muscles of the pinna and the vermiform appendix in man are examples of this type of structure. In a number of mammals other than man the pinna is often useful in catching sound waves and the appendix as a caecum was necessary and useful for the digestion of cellulose. But in man cellulose digestion is done in the prominent colon and the caecum, having lost its usefulness, exists as a reduced organ. The auditory sense of man is very much poorer than that of some other mammals like the dog, and the pinna muscles have lost their function. It is a little difficult to imagine why creation should have bothered to produce utterly useless organs.
The Darwinian factor of selection of the fittest to survive admirably explains the presence of vestigial organs Selection improves an organ to the point of its greatest usefulness. But selection also operates in the reverse direction and so reduction of useless organs can occur. But as reductio

53
continues, at some stage these organs become so minute and insignificant as to have no selection value. After that they continue to exist as vestigial
Organs. m
Summary:
1. In any compact group of organisms the presence of organs with seemingly similar origin can be noted. Adult differences in form are always attributable to differences in function. This underlying similarity of structures very probably 'indicates common Origin.
2. A study of the comparative a natomy of a compact group of organisms like the vertebrates shows a graded sequence from the simple to the complex. While this appearance may be attributed to the whim of a designer, the chances are, along with other supporting facts, that the complex forms arose from forms with a simpler build. This graded sequence can be seen in practically every organ system of the body. That this graded sequence is not necessarily imaginary is proved by the fact that in the development of a single animal like the frog there is a gradual change in structure of the vascular system, for example, from the aquatic to the terrestrial type.
sh
3 The theory of special creation would be hard put to explain the existence of vestigial organs. This can only be explained on the basis that organs which were once useful, having lost their usefulness, tend to become reduced until they have no selection value.

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4. All these add up as evidences of the fact of
evolution of organisms.
C
Evidence from Geographical Distribution
Animals are found in all the continents. There is no region on the land mass entirely devoid of animal forms. From the arid deserts to the thick forests of the equatorial belt, from the bleak arctic north to the steaming tropics, all have their characteristic fauna. The strength of population of animal forms no doubt varies as this is dependent upon availability of food and interaction with other organisms.
But the distribution of animal types is not uniform all over the World. All types of animals are not found in all parts of the world, e.g., kangaroos are found only in Australia, elephants in India, Ceylon and Africa, tapirs in South America and Malaya. In addition to this differential occurrence of forms, other anomalies in distribution also exist.
i. Two regions with very nearly the same climate show different forms. Africa has elephants, antelopes and man-like apes. But Brazil has tapirs, sloths and new-world monkeys with prehensile tails.
ii. Two islands in the East Indies, Bali and Lombok, are separated by only a few miles of sea. These two islands have very different fauna Bali has true carnivores while Lombok has only marsupials or pouched mammals. On

iii.
iv.»
(55
the other hand two widely separated countries like Japan and Great Britain have very nearly similar forms.
Certain animal forms are confined to the southern hemisphere. Marsupials are found in Australia, and as far away as South America. These animals are not found in the living condition any where in the northern hemisphere
Lung-fishes are found only in Australia, South Africa, and South America.
The lemurs have a very restricted range being found only in South India, Ceylon and Madagascar. The burrowing amphibians, coecilians are found only in South India and Ceylon. These anomalies in the distribution of animal forms can be explained in the following way:
Land animals get distributed by migration from place to place. Connected land-masses with very nearly the same environmental conditions tend to show very nearly similar forms. For example the whole of Eurasia north of Arabia and the Himalayas show an even distribution of types.
But continuous land-masses may have differences in topography, climate and vegetation in different regions. High mountain chains, arid deserts, lush river valleys and rain-shadow areas may all exist in one continuous landmass. If all animal forms can withstand all these different environmental conditions equally well, then their distribution on this land-mass must be uniform. But, as will be seen from the

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examples given below, all animals are not tolerant of all eonditions. So, for different animal forms, the conditions they are intolerant of, act as barriers for unrestricted migration. These barriers may be of many kinds,
a. High mountain ranges especially those running east-west act as barriers for migration of running forms. But birds may be able to fly over these. For example, the terrestrial fauna north of the Himalayas approximates to that of Europe, while to the south of it, it is entirely different.
b. Environmental temperature acts as an important barrier for cold-blooded animals. Warm blooded animals like the birds and the mammals are found in all the land-masses of the world. But cold-blooded forms like the amphibians and reptiles have a restricted range. They abound in the tropics where the temperature variation between summer and winter is very little. In the temperate parts of the world their population is thin and in the cold north and south these forms do not exist.
s
c. Availability of water is an important factor governing distribution of animals. The large dry deserts like the Arabian desert and the Sahara act as effective barriers for the free migration of most land forms. This is seen
22 Cold-blooded animals are those whose body temperature varies within wide limits when the environmental temperature fluctuates. e. g., amphibians and reptiles. But the body temperature of the warm-blooded animals is relatively constant irrespective of changes in the environmental conditions, e. g. birds and mammals,

芭?
in America where the fauna north of the Mexican desert is very different from that to south of the desert.
Food supply is a nother conditioning factor in the free migration of forms. Regions with plenty of food support a thicker animal population both in numbers and variety. Lack of food limits free migration.
A number of types living in a restricted area show a 'nature's balance' or interdependence On one another. This interdependence is often developed to such a nice degree that all the types of this area act as a whole and must migrate all together or not at all.
W.
Protoplasm, within limits, is more active at higher temperatures
than at lower ones. As the temperature drops protoplasm becomes less and less active. So cold-blooded animals living in temperate lands, where the temperature variation between summer and winter is great, become inactive in the winter and go into a compulsory winter sleep or Hibernation. This inactivity is forced on the protoplasm by the fall in temperature. So in
the bleak north where the temperature is almost always below
freezing point one should not expect to find the cold-blooded amphibians or reptiles. In fact of the vertebrates, only the birds and mammals are found in these regions, as these are relatively free of environmental temperature and their distribution is mainly dependent on the availability of food.
The interesting phenomenon of some mammals in temperate countries going into a winter sleep or some amphibians like the toad going into a summer sleep' in the arid parts of our country has no relation to true hibernation of cold-blooded forms in temperate countries except that both may be construed as methods of survival under conditions hazardous for life.
The winter sleep of mammals in the cold north can be explaineci on thc basis that the availability of food during this period is limited and conscious reduction of activities lessens energy need and makes for survival. The toad burying itself in the dry summer with over-developed mucous glands in the skia is

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Large oceans are effective barriers for the migration of land forms. Even a small strip of salt water acts as an effective barrier for the distribution of amphibians.
As a result of these restrictions on free migra
tion of animals, larger continents seem to have very distinct faunas. On the basis of the distribution
of
animals, the land m^,8 ses of the world can o be
divided into distinct Z00-geographical realms, each with its characteristic fauna."
l,
The Palaearctic realm
Europe north of Iran and Asia, north of the Himalayas and the Nan-ling range in China.
Moles, lemmings, etc.
The Oriental realm
India, Burma, Ceylon and the East Indian islands With the island of Bali as the south. ern limib. Elephants, lions tigers, tapirs, lemurs, orangutan, pangolins.
The Australian realm
Australia, New Zealand and some islands of the
23
explainable on the basis that the long period of drought may desiccate a moist-skinned animal, and the relative poverty of food supply during this season may help in extinction. The difference between these two types of periodic sleep can be understood if one digs up a toad during this period and leaves it on the ground. It promptly hops away. But if a hibernating snake in the cold nortli is picked and thrown it would still continue to be limp.
It must be remenubered that connected land-masses show a very large number of forms in common. For barriers may not exist for these forms. The term characteristic fauna is only used to indicate special forms, recognizing that columon forns also exist,

4.
59
East Indian Archipelago with the island of Iuombok as its nothern limit. '
Platypus, pouched mammals (marsupials), and the kiwi. No true carnivorous animals are found in this realm, -
The Ethiopian realm
All Africa, south of the tropic of Cancer. Man-like apes, the rhinoceros, hippopotamus, Zebra, quagga, wildebeeste, aard-varks and tapirs.
The Nearctic realm
North America, with the Mexican plateau as its southern boundary. Bisons, weasels and stoats, grizzly bears and rattle-snakes.
The Neotropical realm
Central and South America, south of the Mexican desert. This region includes the West Indies also.
Sloths, armadilloes, a na conda, the puma and the cougar, howling monkeys, llamas and alpacas.
The differential distribution of animal forms can be explained on the basis that the land masses of the World have not always been as they are today. Subsidences of land, elevation of the sea-bed, sudden volcanic eruptions, and natural continental drifts have been constantly changing the contours of the land masses.
24. The line separating the oriental realm from the Australian realm,
Wallace's line, passes betweea the islanls of Bali and LQmbok.

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Connected land masses may get separated, or divided ones joined. These changes are partly responsible for the anomalies in animal distributioli. A few examples to illustrate this are given below,
1. The presence of only marsupials as the representatives of the complex mammals in Australia, can be explained as follows. Once upon a time Australia was connected to the oriental realm. But at that time only marsupial mammals had made their appearance on earth, Subsidence of land occurred probably somewhere between the islands of Bali and Lombok separating the australian and the oriental realms, Evolution of true mammals occurred later in the oriental realm, and with the evolution of true carnivores, the slower, dull-witted marsupials were eliminated in the struggle for existence. Hence we do not find any living marsupial form in the oriental realm but their remains are found in plenty in the rock record. But the marsupials isolated in Australia, have, because of the lack of competition, survived to the present day. Even today Australia has no true indigenous carnivorous forms.'
2. The discontinuous distribution of marsupials and the lung fishes probably indicates that at some time in the dim past the three southern continents had land bridges between them. The differences in fauna between these continents in the present day can be explained as
25. The Tasmanian wolf (Thylacine sp) is a marsupial dog.

6.
due to evolution of forms along different lines, as a result of varied environmental conditions.
The elevation and subsidence of land masses occur constantly on the earth. Even as lately as an year ago a new volcano pushed itself up from under the sea and added a bit of land to Portugal. It does not require much imagination to understand that Ceylon and India were once connected by a land bridge. Burrowing uropeltid snakes (earth snakes with truncated tails) and the burrowing limbless amphibians, coecilians, are found only in South India and Ceylon. The amphibian especially, is very intolerent of salt water and migration from one country to another could only have occurred over land bridges.
So, the apparently anomalous distribution of animals can be explained as being due to changes in the contours of the land masses which had occurred in geological history. As a consequence of these changes, new barriers for migration may appear or existing Ones disappear, The present day distribution of forms is the result of all these changes in the history of the earth.
Island fauna offers supporting evidence for this explanation of the geographical distribution of animals. Islands are of two types, continental and Oceanic.
Continental islands are small land masses separated from nearby large land masses by an arm of the sea. This separation is due to subsidence of land between the island and the

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nearby continent. Great Britain, Tasmania, and Ceylon are continental islands. The fauna of
these continental islands approximates closely
to that of the nearby lahd mass. This is as it should be as before the subsidence of the land between them free migration was possible. But
often the island forms se em to evolve into
slightly different lines compared to those of the nearby land-mass. This difference is directly attributable to isolation and the resultant blunting of the keenness of the struggle for existence.
Oceanic islands, on the other hand, are formed suddenly by volcanic: upheavel of the sea-bed. As soon as they appeared they could not have had any land forms. Land forms present in them now must have been brought in either by accident or design. Trift wood and other natural rafts were the means by which oceanic islands got their fauna. Quite obviously the animal population of such islands must be thin both in numbers and variety. But these few are found to be closely related to forms occurring in the nearby land masses. But isolation and lack of competition makes these evolve along lines very different from those of their ancestral stocks in the nearby land mass. In fact Darwin was led to think of natural selection as the means by which new species originate by his study of the giant tortoises of the Galapagos
islands in the pacific Ocean. These tortoises
have lived for a very long time and have grown enormously. In the mainland the struggle

63
for existence is keener and evolution proceeds at a faster pace. And the more and more agile animals produced there, would have given no quarter to these cumbersome giants if they were to exist together. Protected by isolation they attain very large sizes. But being terres. trial forms living in Oceanic islands they must have been brought in from the mainland sometime. In spite of the differences they show from the mainland forms, there is no doubt that they are related. Hence we need not postulate special creation for the presence of these forms.
The distribution of animal forms on the land masses of the World explains the fact of evolution in the following way:
The differential distribution of land forms over the continents can be explained taking into account existing barriers for migrations and the geological history of the land masses.
Isolation of forms in restricted areas produces forms different from their close relatives in nearby larger land masses. In larger land masses with varied climatic and topographical conditions, the struggle for existence is keener and evolution of new forms occur at a rapid rate, But isolated forms, due to lack of competition exist today as they did at the time of isolation or develop lines of evolution different from those of the mainland. The marsupials in Australia, have existed as such because of lack of competition while they have been

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eliminated from the oriental realm by the agile carnivores. The giant tortoises isolated in oceanic islands have attained large sizes.
The believers in the theory of the special creation of Organisms can still state that organisms were created by a divine force. There is nothing to prevent the divine force from creating marsupials in Australia, and giant tortoises in Galapagos islands and even making them appear closely related to forms in other areas, so that We can continue to break Our heads to prove a basic unity of organisms; a unity which does not exist according to the special creationists. But it is difficult to believe that creation deliberately confined the marsupials and lung-fishes to the Southern continents only or that it should make oceanic island fauna resemble those of the nearby land mass, or for that matter why creation should so finely divide the two islands of Bali and
Lombok in respect of their aniinal populations.
The theory of the evolution of forms by descent with change explains the anomalies in the geographical distribution of forms successfully. As evolution of forms proceeded slowly, the topography of the land masses also changed, These changes sometimes opened up new roads for migration and at other times created barriers for free migration, The effect of the sum of all these changes is the cause of the present day distribution of animals.

65
Summary:
1.
O
1.
Animals are found all over the world. But
all terrestrial forms are not distributed uniformly over the land mass.
In this distribution a number of anomalies seem to exist. Nearby lands have very different fauna and widely separated lands show similar fauna.
These differences in the distribution of animals can be explained by recognizing the existence of barriers to free migration.
Barriers may be of many kinds and what acts as a barrier for one type may not act as such for another.
The land masses of the world have not always been as they are today.
Upheavals and subsidences of land have occurred a number of times, creating new barriers for migration or eliminating the existing ones.
As a consequence, isolation of forms in restricted areas occurs sometimes.
A study of these forms helps us to understand how evolution could ha ve occurred.
Isolated forms show only a slow tempo in their evolution as competition is very little in these restricted areas.
The fauna of continental and oceanic islands support the view that evolution is a fact, So special creation need not be invoked to explain the anomalous distribution of animals. A process of evolution occurring in a GQns:

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tantly changing land mass explains this distribution well.
12. In this sense the geographical distribution Of animals furnishes supporting evidence for the fact of evolution.
EVIDENCE FROM PALAEONTOLOGY
A number of theories have been offered to explain the origin of the earth. All these theories agree that when the earth was formed it must have been very hot, almost gaseous. So, life as we know it could not have existed on it. In course of time the surface of the earth cooled and the earth acquired an atmosphere and climate. Life must have arisen long after this,
The earliest rocks of the earth were formed by the cooling of the molten mass that was earth. These are the igneous rocks. Slowly the Weathering actions of wind and rain eroded these igneous rocks and the sediments got deposited in the valleys. In course of time these sediments hardened to form the sedimentary or stratified rocks. Since erosion and sedimentation are continuous processes, the oldest of the stratified rocks must be right at the base and the youngest on top. But in its youth the earth was rather turbulent. Even now it cannot be said to have become quiet. Wolcanic upheavals may bring lower layers on top or land subsidences may take upper layers below. Erosion of rocks brought up by volcanic action may take them down again to a different level. All these combine to distort the neat picture of arrangement

67
of stratified rocks we should see if the earth had behaved with consistency. In the modern day rocks deposited at different times of the earth's history are exposed at the surface in various places.
Geologists are fairly certain that the age of the earth is well over lo00 million years, This has been estimated by a number of people each adopting a different method. But by far the most plausible answer is given by the radio-active method of estimation.' The relative ages of the various rock strata have been determined by this method and a geological time scale has been drawn up for the sendimentary rocks.
Geological records show that organisms have existed on earth for well over 500 million years. The dead remains of quite a few organisms have often been left in the stratified rocks formed at the time they lived. These discernible remains of organisms found in the rock record are known as fossils.
26. It is now known that radium, uranium and thorium disintegrate in successive steps to produce a stable form. Uranium disintegrates until it produces lead. The rate at which this disintegration takes place is also known. So if in any rock uranium bearing mineral is found, its lead-uranium ratio should give us an easy method of estimating the age of the rock.
1. 1 gm of uranium produces annually 7, 600,000,000 gm of lead.
So y gms of , , s XY gms of lead.
7, 600, 000, 000
XYXT gms of lead. y gms in T years will produce 7, 600,000, 000
So, if the lead uranium ratio is known the time taken to produce this lead would be lead x 7, 600, 000 000 years. у

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Fossils may be of various kinds. In fact any type of discernible remains of organisms that existed once must be described as a fossil, Some examples of fossils are given below.
l. A long time ago there lived giant salamanders, close relatives of modern amphibians. In some of the older stratified rocks their foot-prints are seen. Very probably these foot-prints were left in wet clay and later hardening of the clay into rock preserved these foot-prints perfectly. This should be considered a true fossil as it is the discernible remains of forms which existed a long time ago. .
2. Animals with hard parts like shells or bones have left these in the rock strata of their
period in history.
3. Sometimes the remains of dead animals have been replaced particle for particle by silica, and rocky moulds are formed. These are also fossils.
4. Some animals have been found buried in ice. This keeps them fresh. In fact some close relatives of our modern elephants, the mammoths, have been dug up from ice in Siberia and these were found to be so well-preserved that even their flesh was edible. These are also fossils in the sense that they are discernible remains of organisms which existed long ago.

69
Geological table
Major Periods Time (in Dominant Eras Divisions and millions Life forms life
Epochs of years)
. folocene Man, Rise of world Age of C 0 « * * « S Recent civilizations a.
(Post韶 glacial)
ven : Ice-ages. Evolution of Quarter- || Pleistocene : man-like apes and nary man. Large mammals
become extinct. イ。 沮 Pliocene Anthropoidea
> SqSSqSSSqSqqqSqSqSqSqSqSqqqSqSqSqSSqqSSSSq qqSqqqqSS qSSSS SSq SLSLSLSLSLLLLLS SLSL qq SLqLLLLLSLLLLSLLSSLLSSLLS * ***************** !-----------------------------! 1 ם
Diversification of s 당 Miocene mammals 9, 日 ... .....a........, ...--. ""stri ---------ག ------ ཟ་མ་མ་----- -۔۔۔۔۔۔۔۔۔۔۔۔۔۔۔۔۔۔۔ Rise of higher B محصیحه۹ .9 Tertiary Oligocene 2 ់" 臣 ۔۔۔۔۔۔۔۔۔۔۔۔۔۔۔۔۔۔۔۔۔۔۔۔۔۔۔۔ || | ?؟ n
ט& Eocene 22 Disappearance of pri- 云 c mitive mammals. OriO gin of later mammals,
ဝှိ၃:၃cene Rise of primitive Eocene) amal
Extinction of giant reptiles
69 Late حصي 奖 Cretaceous 으 1116.SOZO1 C Extreme special
ization of reptiles, (υ 目 Giant reptiles 9, 8t همسخ .9 "E R 。 없 Jurassic 25 Pterodactyles and 3. 皋 Early Archaoptery X
mesozoic
Triassic 30 Rise of dinosaurs

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8
70
Eras Major Periods į Tilme (in Life if ; Dominant - a - and millions : 18 İOS ; Divisions Epochs of years) life
Permian 2 Elaboration of terrestrial vertebrates and insects
ج GR
d Late ܵ Palaeozoic 眼 E Carboni- 52 Rise of primitive rep- 9. ferous tiles and insects. Age s
of tree ferns and coal & deposition. Elaborat- 敬} ion of amphibious forms. 沙 g
E C Ya Middle .9 , Devonian 58 Rise of amphibians S Palaeozoic and terrestrial flora 3 : Fishes. c
d 오 } A. # Lung-fishes and 密 Silurian 37 Arachmoids
Early Ordovician 8O Armoured fishes and Palaeozoic giant cephalopods o 照R , 萎 Cambrian 8O Shelled animals
Trilobites °g
'S
È |Life forms scanty 3 C ہ A

Sedimentary rocks have been arranged according to their ages. Fossils found in the various strata, have been studied in detail. And a geological time scale has been drawn up for the fossils.
The stratified rocks have been divided into four distinct eras in geological history. Each era. has been divided into a number of periods.
(a) Primary or Palaeozoic era
These are about the oldest of the stratified rocks. The earliest of these are well over 500 million years in age. This era, covers nearly 30% of the period of the history of life on earth.
The palaeozoic rocks have been sub-divided into a number of periods. They are in the order of their age cambrian', Ordovician, silurian, devonian, carboniferous and permian.
Fossils have been found in plenty in the palaeozoic rocks. In the cambrian rocks fossils of trilobites, close relatives of modern arthropods, are found. In the Ordovician rocks, complex cephalopod remains are found in great numbers and variety. The living pearly nautilus seems to have existed unchanged from that period, but its close relatives like Belemnities and Ammonities are known only as fossils. Even in the Ordovician, fossils of heavily armoured fishes are seen. In the silurian period lung-fishes, amphibious in habit, seem to have flourished. Among the invertebrates, the arachnoids seem to have been Well represented at that time.
27, The names of the rock strata often indicate the places where
they were first seen near the earth's surface.

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The devonian rocks show fossils of true amphibians. The remains of flowering plants also occur in plenty in the devonian rocks.
Giant tree ferns seem to have thrived in the late palaeozoic era. Their fossil remains in the carboniferous rocks are the modern coal seams. Fossils of truly terrestrial types like reptiles and insects are found for the first time in these rocks.
(b) Secondary or Mesozoic era
This era is characterized by the fossils of giant reptiles which seem to have flourished during this era in the earth's history, Fossil remains of dinosaurs are seen in the oldest of the mesozoic rocks, the triassic formations. The jurassic period is notable for two reasons. It was during this period that reptiles began to branch out to form the fantastic forms characteristic of the cretaceous period of the mesozoic era, and for the develop. ment of flying reptiles like the pterodactyles and primitive birds. Archaeopteryx, the oldest known bird, was discovered in the jurassic slate formations of Jura, Solenhafen, in Germany. This animal had feathers like the modern birds and probably had considerable powers of flight. But unlike the modern birds it had teeth in both the jaws, free clawed digits in the fore-limbs and a long tail with rectrices arranged on either side."
28. True flight developed only in four animal groups.
(1) Insects: Here the outer body-wall is drawn out to form the
wings. (2) Pterodactyles: Here the first digit of the fore-limb was elongated and a skin or patagium was developed between the fore snd hind limbs. This skin was supported by the elongated finger, All flying reptiles are now extinct,

73
The cretaceous period forming the late mesozoic era is marked by the extreme specialization of form and structure achieved by the reptiles and their ultinate extinction. Since reptilian evolution reached its Zenith of development in the mesozoic era, it is often described as the age of reptiles.
The dinosaurs, extinct reptiles, seemed to have ranged in length from a mere six inches to nearly 100 feet. Gigantosaurus and Diplodocus were well over 80 feet in length, Brontosaurus was nearly 60 feet long. Stegosaurus and Triceratops, although reaching only a modest 20 feet in length, had fantastic armour plates and spines on their bodies,
Most of the dinosaurs were herbivorous but carnivorous forms like Tyrranosaurus and Ornitholestis also existed in this period.
The reason for the total extinction of these giant reptiles towards the end of the mesozoic era is not quite clear. The following may have been some of the contributory causes.
(i) The evolution of the smaller, quick-witted
mammals towards the close of the mesozoic
era, might have resulted in the elimination of these ponderous, sluggish forms,
(ii) Natural calamities which seemed to have occurred quite often during the beginning of
(3) Birds: Here the wing is a modified fore-limb. It has no free digits. Feathers arc present. Flight feathers on the wings are known as the ramiges and those on the tail are the rectrices.
(4) Bats: These are main mals. Three or four digits of the fore limb are clongated to support a thin skin between thern and the body. ܫ
10

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the tertiary era might have eliminated quite a few. In fact large numbers of dinosaur fossils have been dug up from peat bogs into which these seem to have floundered.
(iii) Changes in climate resulting in thinner vegetation may have made the struggle for existence very tough for the large herbivorous forms.
(c) The Tertiary or the Caenozoic era
The tertiary era is marked by the elaboration of higher animals like mammals and birds. In the palaeocene or lower eocene rocks, fossils of primitive mammals are found. Phenacodus, one of the archaic mammals, was like a small sheep. It had small, tusk-like canines. The molars Were low-crowned and the brain-case Was very small in capacity. The amblypods, hoofed ungulates, attained large sizes although they were very primitive in many other characters. By the late eocene period these archaic mammals became extinct probably because of the rise of higher mammals.
The late tertiary period, comprising the oligocene, miocene and pliocene periods, is marked by the rapid development and diversification of
mammals.
The youngest of the tertiary rocks have been delinited to form the quarternary or Pleistocene
era, W (d) The Quarternary or Pleistocene era
This period in earth's history is marked by glaciations of the polar ice-cap, and so is often terlucd the ice-age. During periods of glaciation

75
the ice from the north crept down almost to the level of the Mediterranean Sea. As a result climatic conditions must have differed radically from what obtains now. The tropical lands must have been much colder during glaciation periods. During periods when the ice-cap retreated to the pole the climate in temperate lands may have been very much warmer than it is now.
Four such glaciations seem to have occurred during the pleistocene period. The first glacial epoch, the Gunz, " was separated from the second, the Mindel, by a short period of ice retreat. This is the first inter-glacial epoch. The Mindel was followed by a great inter-glacial epoch when the ice retreated almost to the pole. This was followed by two glaciations, the Riss and the Wurm, themselves separated by another short inter-glacial period. The present period is described as a post-glacial period although it could very easily be a great interglacial epoch. s
During the pleistocene period, the large mammals like the mastodon, Woolly mammoths, and imperial elephants became extinct. Before the descent of the ice-cap, the now temperate lands must have been much warmer and thick forests must have existed in regions which are now grass-lands. The larger mammals which roamed these forests must have become extinct as glaciation occurred.
It was during the lower pleistocene period that man-like apes attained elaboration and somewhere during the middle pleistocene period man originated.
29 European terminology has been adopted for ice-ages as those
terms are simpler than others in use.

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ገሰ
The post-glacial era, known as the psychozoic or recent era (holocene), is marked mainly by the rise of World civilizations,
Periods Sub-divisions
Holocene į Post-glacial
Upper Wurm. Fourth glacial pleistocene ||
3rd inter-glacial
Riss - Third glacial Middle -ܚܚܚܚܚܚܚܚܚ- ܫܫܫܝ
pleistocene Great inter-glacial
2nd inter-glacial
Mindel - second glacial Lower -------
lst inter-glacial pleistocene --------------
Gunz - First glacial
Ice - Ages
The following inferences can be drawn from the study of fossils seen in the rock record.
i. Since representatives of all major animal groups are found in the cambrian rocks themselves, life must have existed much earlier although many distinct fossils of these forms
have not been obtained.

ii.
iii.
1ν.
t
There is a distinct chronological sequence in the order of appearance of forms. For example, among the vertebrates fishes are known from the earliest rocks, amphibians appear from late palaeozoic onwards, reptiles from the mesozoic and birds and mammals from late mesozoic onwards. This order of appearance seems to agree with our modern scientific classification of animals based on a recognition of progressively increasing complexity of structure. In fact the rock record seems to bear out our contention that even within each phylum there is a graded sequence in complexity of structure.
While all this does not form positive proof of the fact of evolution of more complex forms from simpler ones, it is difficult to believe that this nice correspondence and graded sequence mean nothing and that each form was created as a distinct entity.
While the rock record is necessarily incomplete as a number of forms must have failed to get fossilized, an understanding of how earlier forms existed does give an idea of
how modern forms could have originated from
them. This is particularly clear in some instances where a fairly complete set of fossils
have been obtained, which lead gradually from ancestral types to modern forms. One such example is pro vided by the evolution of the modern one-toed horse, Equus. This is shown in tabulated form below,

Page 45
ܚܝ
IPeriod
Plio Conne
۔۔۔۔۔۔۔۔۔ـــــــــــــــــــــسی۔۔۔
Miocene
loligocene
EOCeme
Years in millions
14
------سسس--- )
12
22
Type
Characters
Equus
Feet one-toed. Teeth long and columnar. Enamel in intricate pattern. Limb unguligrade.
Plessippus
Mesohippus
Orohippus
Eohippus
Mer y chippus 3 toes in each limb, but
Size roughly that ol a modern arab horse.
Teeth have longer crowns as in horse. No.
lateral tOeS. ●
the lateral toes do not reach the ground and so functionally one-toed Teeth almost like those of modern horse.
About 18' high. Three
functional digits in both limbs. The pre-molars have become almost molar-like.
Splint bones in forelimb completely lost. Middle toe in fore-limb enlarged. Outer fingers on fore-limbs shortened. Teeth becoming more like that of a horse.
|Height about 12'. Four toes in fore limb with a splint in place of 5th. 3 toes in hind limbs. Cusps on molars tend to fuse.

*g
This graded sequence seen in the evolution of a horse could not be accidental. Such colnplete fossil sets have been obtained to show the evolution of the camel and the elephant also. If this could be true of one animal, the chances are that such an evolution has occurred in the origin of other forms also.
In discussing evolution of organisms it must be distinctly understood that one modern form has not directly arisen from another form which existed before. For example, it would be wrong to say that the modern horse originated directly from the pliocene horse, the plessippus, but it would be correct to say that both have evolved from common ancestors. When ancestry is mentioned we are thinking of stocks and not of individuals. So the search for exact missing links connecting two individuals or two groups is futile for these could not have existed.
The science of palaeontology (old history of individuals) thus gives fairly substantive evidence of the fact of evolution of organisms.
Summary:
1. The earth must have been very hot when it was for ined and lific as we know it could not have existed at that time.
2. As the earth cooled and climate set in, rock strata were laid Qn, one over the other. The relative ages of these rock strata have been estinated.
3. In these stratified rucks remtuins of animals

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80
0.
which existed during the various periods of rock formation are found. These are the fossils.
All arrangement of these fossils according to their ages is possible as the ages of the rocks
where they are found are known,
This arrangement shows distinctly that there is a chronology in the Order of appearance
of forms. It also shows a graded sequence in
increase of complexity of structure.
The order of occurrence of the fossils also shows that our modern systems of classification of animal forms is scientifically correct in as much as it seems to reflect the racial history of forms in the geological time scale,
The fossil record is necessarily incomplete as quite a number of forms may have failed to fossilize. But in a few forms a nicely graded series of fossils have been obtained and these show the line of evolution of modern forms from ones that existed before
The chances are that what is true for one
type is true for all organisms and it is only the incompleteness of the fossil record that prevents us from seeing the entire picture.
While it is still not impossible to assert that all organisms were separately created, it is difficult to understand why creation should have bothered to produce this nicely graded Scquence. So, palaeontology along with other evidences con pels one to belie ve til at orga luisins have evolved and Wcre i u Ubi created,

9.
E
Evidence from Embryology
The early developmental period in the life of a metazoan animal seems to pass through a number of steps which, in Organization, appear to be sinilar to the major steps passed by the race itself in its history. This similarity in steps led Von Baer (1792-1867) and Ernest Haeckel (18431919) to state that in the development of organisms there is a fair amount of recapitulation of racial history. This idea was terned by Haeckel as the law of biogenesis or the theory of recapitulation.
This law states “ontogeny recapitulates phylogeny. To put it more simply, the developmental stages of metazoan organisms recapitulates or remembers and reproduces the steps passed through by its race in evolution,
Even if true, this recapitulation of racial history can never be exact, as steps passed through in millions of years in racial history cannot be reproduced faithfully in the relatively short period of the development of an animal. At best it can only be of the very major steps in evolution.
Recapitulationists adduce the following points as evidence of the truth of their belief.
(1) All vertebrates start life as a single cell, the fertilized egg or zygote. This cell divides repeatedly to form a mass of cells. These cells stay together and arrange themselves round a single central space within the body, Later by soruututive u U veuen bis and foldings of cycllo

Page 47
(2)
layers, they reach a stage in development, where three primary cell layers each one, one or many cells thick can be recognized. A completely closed space is developed in the middle of the cell-layers. Later axial structures like the nervecord and the notochord are laid down and gradually the adult form and structure are obtained.
These steps in the development of an individual meta Zoan seem to have comparable steps in the evolution of organisms from the simpler forms to more complex ones. The single celled stage in development seems to be comparable to the protozoans whose bodies are
just independent specks of protoplasm. The
two cell-layered stage in development, with a single internal cavity is comparable to the organization of the modern coelenterates and a three cell-layered stage with central gat and surrounding coelon or body-cavity to the modern coelomates.
During the development of terrestrial vertebrates certain totally non-functional structures like the gill-pouches connecting the gut to the outer space are developed. In aquatic vertebrates like the fishes, these gill pouches have a function. Their lifting membranes become vascular and as water passes over them, they function as respiratory surfaces helping in the exchange of gases, But during the embryonic de velopmeut of terrest rial vertebrates these gill pouches have no function aud their presence cin only be attributed to a lluesita ut

(3)
S3
memory of racial history where structural adaptations developed to meet environmental hazards.
There is sufficient evidence to believe that life originated in the sea and that colonization of land by organisms occurred later. The jump from an aquatic to a terrestrial habit appears to be very abrupt as the conditions of living are very different in these two habitats. But the change over in structure necessary for a terrestrial habit occurs in the life-history of a modern amphibian like the frog. They pass
through three steps.
(a) They develop vascular surfaces which serve for the exchange of gases with the Water in which they live.
(b) Then their structural organization changes so that they use both atmospheric oxygen and the oxygen dissolved in water for their respiratory needs.
(c) Finally they develop into forms which use atmospheric oxygen for their respiratory needs.
Recapitulationists assert, that if this radical jump from a purely aquatic habit to a terrestrial one could occur even within the very short span of the life-history of one particular form, it could very well have occurred in racial history also, and the individual in its development just retraces the same steps passed by its ancestors as these have been proved to be successful,

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84
(4) Adult forms are often very highly specialized
for their modes of life. But developmental or larval stages are less specialized. A comparison of the structures of larval forms shows similarities. This does indicate common ancestry.
In fact the position in the tree of life of quite a few organisms are determined on the basis of their larval forms and not on adult stuctures which show radical differences.
For example, Sacculina, a crustacean parasite on crabs, in its adult stage consists of just a bag with cells and a large number of fine threads which enter into the body of the crab and absorb nourishment from it. In this stage its structure does not seem to have any relationship to any particular group of organisms. But during its development it passes through a larval phase, the nauplius larva, with three pairs of jointed limbs and a sensitive eyespot. This is a characteristic larva of the crustaceans. The occurrence of this larva in life-history is indicative of recapitulation of racial history.
The sea-squirts, ascidians, living attached to piers and boats and looking like lumps of clay actually belong to the major animal group to which wise man himself belongs, the chordata.
In its adult state it has neither notochord
nor nerve-cord. But in its developmental period it passes through a frec-living larval state with well developed tail, nerve-cord
and notochord. Later a sort of retrogressive metamorphosis takes place to produce the

)
ጽ55
adult form. Here the larval form indicates relationship with other chordates implying thereby common ancestry with them.
In addition larval forms often indicate relationship between different groups of animals. The velliger larvae of molluscs are not very different from the basic trochophore larvae of. the annelids and this similarity probably indicates that modern annelids and molluscs have
diversified from common ancestral stocks. This
correspondence between larval forms of different groups is so great that one larval form may easily be mistaken for another. In fact the bipinnaria larvae of the star-fishes have quite often been confused with the tornaria larva of the pro-chordate form, Balanoglossus,
This correspondence in the structure of larvae belonging to different groups can be successfully explained on the basis, that when diversification of forms occurred in geological history, steps corresponding to the present
day organizations of larval forms were passed through before modern animal forms arose
And a modern form developing from a simple protoplast retraces most steps of its racial history as these have been proved to be advantageous for survival. ר
In one variety of snails, the adults have smooth shells. But during their life-history they start with smooth shells, then develop ridges on the shell. Then these ridges elabo
rate into intrica te patterns. After this the

Page 49
(1)
sculpturing becomes slowly reduced until the adult smooth shell is obtained. .
The shells of snails found in the rock record also show this sequence. Earliest shells are smooth, later shells by successive steps attain elaborate sculpturing. Still later the sculpturing is less and finally smooth-shelled forms are seen. The development of all these steps in the life-history of one modern form is indicative of recapitulation of racial history. An assessment of the evidences adduced to prove the truth of the theory of recapitulation.
It is not quite correct to compare developmental stages of modern forms with other modern adult forms, as adult animal organization is often a case of extreme specialization to meet environmental conditions successfully. Even straight-forward comparisons of less speciallized developmental stages can be wrong as even their structures are often adaptations for special modes of development. For example the development of external gills and other embryonal organs have no correspondences. with forms found in racial history. The fluid
filled amniotic cavity formed during the develop
ment of terrestrial vertebrates cannot bé thought of as a piece of recapitulation of racial history, the individual trying to create an artificial sea round it, to remember its ancient aquatic
ancestors, but as a special adaptive structure,
developed to meet hazards inherent in terrestrial development.

87
(2) With all these drawbacks development of
modern organisms does offer evidence of common ancestry for a number of forms. The biogenctic
law should not be understood as meaning that all steps passed through in the racial history
of an organism are faithfully reproduced in ontogeny, but only as meaning that diversification of complex forms could have occurred froln simpler ones through steps comparable to the elaboration of a complex adult form from the very simple unspecialized Zygote, thus bearing out the fact of evolution of Organisms,
Summary:
l.
The developmental stages of modern complex forms seem comparable to forms with simple organization.
These steps seem to have comparable stages in racial history also.
So the development of a modern form inay be taken as showing, necessarily in a condensed form, the steps passed in racial history by this form.
This recapitulation, seeins true specially when useless structures are developed during developlilent.
Less specialized larval forms show similaritics in organization within members of one grotlp and sounctiines between those of different groups. This probably indicales coluluop auccsbry,

Page 50
F
Evidence from Comparative Physiology
A single speck of protoplasin, the basic material of living forms, performs all functions of life cffectively. But the development of complex organs to make living possible in varied environments bring with it specializations in the working of these organs. These, like the structural specializations, are often in the nature of adaptations for survival in varied habitats.
Life seems to ha ve origina, tcd in the sea. Tluis belief is based on the following evidence.
i) The body fluids of animals, both aquatic and
XV C terrestrial, are similar in composition.
(ii) The composition of body fluids is very nearly
like that of sea water.
(iii) The sea is one of the most favourable environ
ments for life because
(a) it is a relatively uniform environment. For example, the variation in temperture between the arctic seas and tropical ones is not very much more than 2c.
(b) it has an abundance of food.
(c) its buoyancy helps the mechanical function of supporting the mass in animals. This makes the attainment of large sizes possible. For example, no land animal can ever reach the sizes attained by baleen whales. They would be crushed by their own
Weight,

ts9
(iv) There is no risk of the sea drying up.
(v) Although body fluids have more potassium and less Inagnesiu in than sea-water, thcre is evidence to believe that the ancient seas had a like composition.
The evolution of terrestrial forms involves the development of not only special structural adaptations but also functional Ones. The major problems which confront terrestrial forms are (i) the risk of Water loss and consequent desiccation, (ii) the difficulty of keeping the composition of
body fluids constant.
These hazards have been overcome by the following functional specializations. (a) Water loss is prevented in a number of
ways. The throwing out of metabolic waste has to be done along with water. But in
doing this, terrestrial forms lose the very minimum water. The nephridia of earthworms re-absorb most of the water that comes in with excretory matter. In fact the length of nephridial tubes and even the entero-nephric condition where water along with waste matter is poured into the alimentary canal so that the water may be re-absorbed by the lining membrane of the alimentary canal, are terrestrial adaptations. Likewise the length of the malpighian tubules in vertebratics helps to re-absurb uust ul ulhe water.

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90
(b) Complexity has been achieved even in the type of excretory matter thrown out. Marine animals deaminate proteins and form ammonia. Ammonia is highly soluble in water and poisonous. But the body fluids and surrounding water are isotonic and so there is free permeability and ammonia is washed out easily and quickly. Such a thing cannot happen in fresh-water or terrestrial vertebrates.
These animals deaminate proteins and after storing glycogen, synthesise the nitrogenous waste into urea or uric acid,
Urea is a harmless substance and a longer time can be taken in its elimination with lininimum of Water loss. Amphibia, for exaluple, throw out excretory products as urea.
But in completely terrestrial animals like reptiles, birds and insects even this water loss is sought to be avoided by converting excretory waste into uric acid or urates. These are practically insoluble substances. This makes possible the re-absorption of all water which tends to go out with Waste matter and the passing out of selli-solid nitrogenous Waste.
So structural complexity Which helps survival in hostile habitats is always accompanied by corresponding de velopment of physiological conplexity. But basic unity in functional organization is indicated by the composition of body fluids and the developillclut of certain basic materials like cytochronic to perfor ill the Work of releasing energy.

91
So, descent with change, is not seen only in structures, Functional specializations also seem to diversify from a basic condition as adaptations, In this sense comparative physiology offers another evidence of the fact of evolution.
Summary:
(1) There is a graded series of increasing complexity in functions, accompanying the increase in structural complexity.
(2) This complexity in physiology is in the nature
of adaptations to habitats.
(3) The basic similarity of body fluids of marine
and land forms indicates common ancestry, the differences being attributable to specialis zation for survival in varied habitats.

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92
8
Man in Evolution
Homo sapiens, wise man, is almost the latest animal to arrive in the geological time scale. He is a mammal as he suckles his young with milk produced by mammary glands. Mammals include bats, dogs, rats, horses, elephants and a host of Other animals.
ln modern classification man is placed in the order Primates under the class Mammalia. Primates include, along with man, lemurs, monkeys and apes. Primates have four generalized limbs. Each limb has five digits and each digit ends in a nail. Primates usually have two milk-secreting glands.
The sub-order Anthropoidea under the primates includes monkeys, apes and man. Anthropoids have flat or cupped nails.
The sub-order Anthropoidea is divided into two super-families, Ceboidea to include the monkeys and the Hominoidea to include man and main-like apes. Hominoids do not have cheek pouches or tails.
Hominoids in turn are divided into two families the Pongidae including the apes and the Hominidae including modern man and fossil men. In the present day there is only one living species of man, Homo sapiens, wise man. All men in the world belong to this species, whatever their colour, creed, culture and crudities may be.
The major differences in structure between apes and man are tabulated below.

PONGIDAE
HOMINIDAE
4.
10.
11.
12.
13.
limbs are
Limbs long
Arboreal habits. Swing from tree to tree with the help of long arms (Brachiation). All four used while walking on the ground. They shuffle along on the soles of the hindlimbs and knuckles of fore-limbs.
Fore-limbs longer than hind-limbs
Thumbs not well apposed to other fingers
Powerful voice
Bones massive
Bodies hairy
Nose appears flat as the snout is more pronounced
Neither chin nor face
well developed
Brow-ridges very promiment almost forming a hood over the eyes
Teeth large. Canines or tearing teeth sharp
The dental arcade appears truncated in front and divergent at the angles of the jaws
Average brain capacity
is about 500 cc.
10.
1.
12.
13.
Limbs relatively short Pesture erect, Walk on
two legs. Fore-limbs freed from locomotor function.
Fore-limbs shorter than hind-limbs Thumbs distinctly apposed. to other singers Voice mild
Bones light
airs scant
Snout withdrawn and nose appears prominent
Chin and face prominently present
Brow-ridges absent.
Teeth small. Canines are spoon-shaped and function almost as cutting teeth, the incisors.
The dental smooth arch.
arcade is a
Average brain
capacity is about 1400cc.

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94
Origin of man in the geological time scale
Fossil evidences show that anthropoids diversified very rapidly during the pleistocene period, the time of the ice-ages. During glaciations, parts of the earth now arid, must have been lush forests, a congenial environment for apes with their habit of swinging from tree to tree by their fore-limbs. The retreat of ice in the inter-glacial periods must have thinned these forests and forced the arboreal apes to come down to the ground. Having come down, some of them must have decided to stay on the ground.
So, very probably man-like forms originated during the great inter-glacial period of the pleistocene. Fossil evidences substantiate this view.
The place on earth where man-like forms appeared first is still an open question. For long, Central Asia was held to be the region where he originated. The discovery of primitive man-like forms in Africa and India made some authorities name these countries as the birth-place of man. Egypt with some of the earliest civilizations and East Indies with its fossils of sub-human forms seem to have equal claim for this honour. Only the discovery of a more complete set of fossils in the line of human evolution can settle this issue.
Fossil remains of man-like forms
The fundamental character that distinguishes man from man-like apes is the possession of an erect habit, using only the hind-limbs for locomotion. Fossil remains of human forms which had

95
an erect habit are known in plenty. They also show a graded sequence leading on from ape-like characteristics through slow steps to those of modern wise man. The more important of these forms are Australopithecus africanus, Pithecanthropus erectus, Homo neanderthelensis and finally Homo sapiens." A comparison of their characteristics is tabulated in the next page.
A study of the tabulated characteristics shows clearly the graded sequence in the origin of modern man. Homo neanderthelensis was probably an offshoot from the main line of human evolution. The famous quip of the Victorian era, “You leave me and my ancestors in beaven and I will leave you and your ancestors in the Zoological gardens,' had only human Vanity to back it but no scientific data to support it.
As already stated the distinctive character of nian is the erect posture. This releases the hands for work. This in turn improves the association centres of the brain. Lighter jaws make for freedom of movement of the tongue and jaws. Speech develops and this improves in its turn the intelligence and the Work done With the hands. With the development of speech, abstraction of
30. Australis (L) = Southern, Pithecus (G) ** ape-South African ape
IPithecos - ape, Anthropos – man - Apc-man Australopithecus africanus: A small skull in limestone was discovered in 13echuanaland, South Africa in 1925, Investigation of this skull was done by Professor R. Dart, Pitl ccantlı ropus erectus: Middle pleistoccne. A skull-cap, thiigla bonc and two ceth werc discovered first by Dr. Dubois of l lollaud letween the years 1890 and 1892 at Trinil on the river Sol o in Java, Homo leanleitheleusis: 'ussil skeletous were first discovered at Neaudicio (Ludl iu Wes 4 U vi nuda uy iu lö 56.

Page 54
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97
ideas occur. Experiences are shared. A gregarious habit with common experiences makes for division of labour and consequent improvement of the efficiency of the entire group. Social organization gives him leisure and thought makes him conscious of the fact that he has a history. Culture and civilizations develop.
Future evolution of man
Man is the only animal conscious of the fact that he has evolved as a result of inter-action between living organism and its environmentTo the extent he is conscious of this fact he is a master of his physical evolution. So no radical changes in physical characteristics may occur in his future evolution. Very probably he may lose all hair and teeth as neither of these are used to any great extent.
His future evolution can only be social. If he continues to see only the differences between men, based on crude vanities of colour, race, culture and language, his survival as a race appears doubtful. The use of tools, one of the basic characters of humans as different from apes, has made him develop tools of destruction which can destroy all life on earth Homo sapiens evolved from lower animals. Whether or not he has evolved noW into a new species - Homo ignoramus, can be decided not by judging physical characteristics but only by judging his behaviour.
3. Huxley's answer to this quip was that he would rather be
icy centlel from an intelligent monkey than from a foolish Angel.

Page 55
Printed at the Sri Lanka Printing Works, Jaffua.
 

Page 56


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