Part 3 (2/2)
The questions insistently call for an answer: How could these instincts preserve the animal when they were still in an incipient, undeveloped state? How could they arise through natural selection (which is simply _accident,_ of course), at all? Darwin says that there are instincts ”almost identically the same in animals so remote in the scale of Nature, that we cannot account for their similarity by inheritance from a common progenitor, and consequently must believe that they were independently acquired through natural selection.” Again he says ”Many instincts are so wonderful that their development will probably appear to the reader a difficulty sufficient to overcome my whole theory.”
And here, in the vernacular of the day, we would depose that Mr. Darwin _”said something.”_
CHAPTER SEVEN.
Heredity.
The subject of heredity is intimately bound up with the evolutionary hypothesis and, it must be admitted, creates a new difficulty for the acceptance of the theory. Indeed, the laws of heredity, so far as understood, appear to contradict the theory of Lamarck and Darwin at a vital point, if not at _the_ vital point of the entire structure raised in the _”Origin of Species.”_ It is necessary in order to appreciate the strength of this objection, to recall once more the outstanding features of the hypothesis by which scientists have attempted to account for the variety of living forms. The various theories of organic evolution, whether Lamarckian, neo-Lamarckian, or Darwinian, are based upon the a.s.sumption that animals and plants have a tendency to perpetuate by transmission to offspring a variation which has proven useful as an aid to the particular species in its struggle for existence. We have just discussed, in the chapters on the Fixity of Species and on Rudimentary Organs, certain difficulties which loom up when the question is raised, How did varieties become distinct species? However, even if it were to be a.s.sumed that some satisfying answer might be found to this question so far as the stages of incomplete organs are concerned, there is one fact in heredity which, it would seem to me, strikes at the very heart of the theory.
In his _”Philosophic Zoologique”_ (1809), Lamarck first explicitly formulated his ideas as to the trans.m.u.tation of species, though he had outlined them as early as 1801. The changes in the species have been wrought, he said, through the unceasing efforts of each organism to meet the needs imposed upon it by its environment. Constant striving means the constant use of certain organs, and such use leads to the development of those organs. Thus a bird running by the sea-sh.o.r.e is constantly tempted to wade deeper and deeper in pursuit of food; its incessant efforts tend to develop its legs, in accordance with the observed principle that the use of any organ tends to strengthen and develop it. But such slightly increased development of the legs is _transmitted to the offspring_ of the bird, which in turn develops its already improved legs by its individual efforts, and transmits the improved tendency. Generation after generation this is repeated, until the sum of the infinitesimal variations, all in the same direction, results in the production of the long-legged wading-bird. In a similar way, through individual effort and _transmitted tendency,_ all the diversified organs of all creatures have been developed--the fin of the fish, the wings of the bird, the hand of man; nay, more, the fish itself, the bird, the man, even.
Note well, the fundamental a.s.sumption is that such acquired characteristics,--greater length of leg, or of neck, a coating of hair, a protective coloring, etc.,--however acquired, can be transmitted from the parent animal possessing them, to its offspring. The question arises: Can such characteristics be transmitted? And the students of heredity answer: They _cannot!_
I find in G. Archibald Reid _”Alcoholism, a Study in Heredity,”_ a lucid exposition of this subject. (Reid is a F. R. S. E. His book was published by T. Fisher Unwin, London, a few yars [tr. note: sic] ago.)
”All the characters of a living being, every physical structure and every mental trait, may be placed in one of two categories. Either they are inborn or they are acquired. An inborn or innate character is one which, in common parlance, arises in the individual 'by nature.'
Thus arms, legs, eyes, ears, head, etc., and all inborn characters.
The child inherits them from his parent. But, if during its development, or after the completion of the development any one of the inborn characters of an individual is modified by some occurrence, the change thus produced is known as an acquired character, or, shortly, as an acquirement.
”Thus all the effects of exercise are acquirements; for example the enlargement which exercise causes in muscles. The effects of lack of exercise are also acquirements; for example, the wasting of a disused muscle.
”The effects of injury are acquirements; for example, the changes in a diseased lung or injured arm. Every modification of the mind is also an acquirement; for example, everything stored within the memory.
”If a man be blinded by accident or disease, his blindness is acquired.
But if he comes into the world blind, if he be blind by nature, his blindness is inborn. If a son be naturally smaller than his father, then his inferiority of size is inborn; but if his growth be stunted by ill health or lack of nourishment or exercise, his inferiority is acquired.
”Lamarck held, as people in all ages have held, that characters acquired by parents are also transmissible to some extent, and that evolution results from their accentuation during succeeding generations. _Lamarck's theory is rejected totally by the modern followers of Darwin_.
”Ten thousand men might break their fingers, yet among their offspring not one might have a crooked finger. Consider on the other hand for how many generations women have bored their ears and noses in India. Yet when is a girl born with ears and nose already pierced? For how many generations have we amputated the tails of terriers, and yet their tails are no shorter. It will then be perceived how overwhelming is the case against the doctrine of the transmission of acquirements.
”The general question of the transmission of acquirements is too big and too abstruse to be treated adequately here. Two arguments more I may use, however, partly because they have not been developed, to my knowledge, by other writers, and partly because they seem to me well-nigh decisive. The more than normal development of the blacksmith's arm is rightfully called an acquired trait, since it arises from exercise, from use, not from germinal conditions. But no infant's arm develops into an ordinary adult arm without exercise similar in kind to that which develops the blacksmith's arm, though less in degree.
”Every single thing contained within the memory of man, every single word of a language, for instance, is an acquirement. But when are the contents of a parent's mind transmitted to the child?
”Again, a man is capable of becoming a parent at any time between extreme youth and extreme old age; a woman from the age of thirteen to fourteen till nearly fifty. Between the birth of the first child and the last such an individual changes vastly. Under stress and fear of circ.u.mstances, under the slings and arrows of outrageous fortune, all sorts of acquirements are made. The body becomes vigorous and then feeble, the mind grows mature, and then senile. He or she grows wrinkled and bowed and perhaps very wise, or perhaps much the reverse.
Yet no one viewing a baby show, a children's party, or an a.s.sembly of adults, of whom he has no previous knowledge, can say which is the child of the youthful and which of aged parents.
”Apparently, therefore, the whole of the parent's acquirements have no effect on the child. _Surely no evidence could be stronger.”_* [[* The undoubted transmission of siphilis [tr. note: sic] to off-spring might be regarded as a case of transmission of an acquired characteristic. But the case is not in point since congenital siphilis [tr. note: sic] is, properly, due to a prenatal infection, the bacillus entering the very germ-plasm of the human ovum (egg). Medical science, generally, has become very cautious in the use of the word ”hereditary.” There is almost unanimity among medical men in the denial of heredity as a factor in tuberculosis and cancer. Most physicians are honest enough to say that they know considerably less about these things than was ”known” ten and twenty years ago.]]
Herbert Spencer claims that ”the inheritance of acquired characters” is a necessary supplement to natural selection. ”Close contemplation of the facts impresses me more strongly than ever with the two alternatives--either there has been inheritance of acquired characters, or there has been no evolution.” Again, ”the inheritance of acquired characters, which it is now the fas.h.i.+on of the biological world to deny, was by Mr. Darwin fully recognized and often insisted on.” ”The neo-Darwinists, however, do not admit this cause at all.” He admits that known facts which show that acquired characters are inherited are few, but he thinks that they are ”as large a number as can be expected, considering the difficulty of observing them and the absence of search.”
From the above, we see that the biological world is against Mr.
Spencer's view; that he would abandon the theory of evolution unless acquired characters had been inherited, but that facts in support of this theory are meager. ”Biologists in the above instance, as well as in others, differ in theory as to fundamental principles of evolution. He who imagines that the theory of organic evolution has been proved to the point of demonstration, has but to read the contentions of evolutionists themselves with regard to the most important things involved in the theory, in order to satisfy his mind that there is great diversity of opinion.” (Fairhurst.)
The general abandonment of the Darwinian hypothesis by biologists, adverted to in our next chapter, is mainly due to the failure of heredity to account for the gradual modification of organs and of habits.
Various expedients are resorted to by Haeckel and a few others in their attempts to bolster up a theory which has broken so signally on the rock of heredity. Princ.i.p.al among these is the reference to unlimited time. It is a.s.serted that, after all, such minute differences might, in the course of many ages, result in new and more perfect organs. However, here a new and unexpected difficulty presents itself. The physicist, who has measured the heat of the sun, rises up and says that the age of the earth, as estimated by specialists like Lord Kelvin, is not nearly so great as is demanded by the Darwinian. The period which the physicists, in their mercy, appear to be willing to grant the inhabitable globe is from twenty to forty million years. But the evolutionists maintain with great fervor that this period is far too short for the production of such complicated types of organism as now live on the earth; they demand from two hundred to a thousand million years! And so these two groups of scientists, the evolutionistic biologist and the physicists are hopelessly at odds.
A new generation of evolutionists has within the past twenty years arisen which holds that the changes in the organizations of plants and animals do not come by slow growth of favorable characteristics, but arise suddenly. Such is the ”Mutation” theory of Hugo de Vries. But science has failed to receive this and similar theories with the same acclaim which once greeted Darwin's _”Origin of Species.”_ Naturalists have become cautious. They remember the inglorious collapse of the Darwinian regime and they are slow to hail another ”Abraham of scientific thought.” They are, in a general way, believers in some kind of evolution; but they prefer not to specify exactly the laws which have been operative in past ”geological time.” It is only in high-school texts in physical geography, zoology, and botany, that the evolutionary theory as propounded by Darwin is still treated as if it enjoyed among scientific men the same respect as the multiplication table. Speaking in the Darwinian dialect we should say that the authors of these school-texts const.i.tute a case of ”arrested development.”
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