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down to the offspring their advantageous condition of structure and physiology." 32

Darwin thought that the lowest forms of life appeared first. Through reproduction, variation and struggle there resulted a slow, gradual, continuous evolution to the higher forms until man was reached. He saw that man by artificial selection decided what types of domestic plants and animals should survive, but he thought that natural selection had determined earlier evolution in the main. To this, however, he added sexual selection resulting from the choice of mates which in some measure he thought had been a determining factor. Later on he was inclined to believe that perhaps the environment produced some changes directly. Darwin put man also wholly under the law of natural selection, but Wallace felt that his psychical nature could not be accounted for on this basis.

As was hinted at the first of the chapter the fact that Darwin established the principle of evolution by his observations by no means implies that his explanations of the methods or causes will stand. At first so overwhelming was his evidence, so entrancing the new view of life that many of his followers went to far greater lengths in asserting the finality of his ideas than did Darwin himself. Against these claims as well as against some of his own ideas there was bound to come a reaction. has come and in recent years there have been many death notices of Darwinism written. The reader should not, however, fall into the gross mistake of thinking that opposition to Darwin involves opposition to the concept of evolution. So far as students can see today this idea is here to stay.

32 KELLOGG, V. L. Darwinism To-day, p. 13.

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As Kellogg says in the first chapter of "Darwinism To-day": "To too many general readers Darwinism is synonymous with organic evolution or the theory of descent. The word is not to be so used or considered. Darwinism, primarily, is a most ingenious, most plausible, and, according to one's belief, most effective or most inadequate, causo-mechanical explanation of adaptation and species-transforming . . . the fact is that the name Darwinism has been pretty consistently applied by biologists only to those theories practically original with Darwin which offer a mechanical explanation of the accepted fact of descent. Of these Darwinian theories the primary and all important one is that of natural selection. Included with this in Darwinism are the now nearly wholly discredited theories of sexual selection and of the pangenesis of gemmules. 33 The fair truth is that the Darwinian selection theories, considered with regard to their claimed capacity to be an independently sufficient mechanical explanation of descent, stand today seriously discredited in the biological world. On the other hand, it is also fair truth to say that no replacing hypothesis or theory of species-forming has been offered by the opponents of selection which has met with any general or even considerable acceptance by naturalists." 34

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For present purposes we need only say that Darwin was primarily interested in results: the later students are dealing largely with origins. The newer interest is in heredity rather than evolution and this topic will be treated in the following chapter.

In an earlier section attention was called to the rapid rate of reproduction and the interrelations of the different 33 KELLOGG, V. L. o. c., pp. 2 and 3.

34 Ibid., p. 5.

forms of life. We must now consider some of the evidence offered to show that there is a selective process in the elimination of individuals or types.

It is readily seen that no selective elimination results from the tornado which kills all in its path save such as chance to be sheltered, to the lightning which strikes by chance, nor to the stream which suddenly going dry destroys all the fishes that chance to be therein. It must be admitted also that many characteristics of animals are negative so far as can be seen. The difference of an inch in the length or a pound in the weight of a cow is meaningless. No one claims that the passenger pigeon perished because it had twelve feathers in its tail or that the mourning dove survived because it had fourteen. If however in the country infested with the tsetse fly cattle appeared, whose skin was so thick that the proboscis of the fly could not penetrate it, the little difference would be very important the thick-skinned type would live, the thin-skinned be killed. We can find some actual illustrations.

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"With silk threads Cesnola tethered forty-five green praying mantises to green herbage, and sixty-five of the brown variety to withered plants. He watched them for seventeen days and all survived unnoticed by birds. But when he put twenty-five green ones among brown herbage all were killed by birds in eleven days, while of forty-five brown ones on green grass, only ten survived at the end of seventeen days. Here we have definite proof of a selective death-rate, definite proof of the selective value of the protective coloration.” 35

"Poulton and Saunders fastened 600 pupa of the tortoise shell butterfly (Vanessa urtica) to nettles, tree35 THOMSON, J. A. Darwinism and Human Life, p. 199.

trunks, fences, walls, and so on. At Oxford there was a mortality of 93 per cent, pointing to an extremely high elimination-rate, and the only pupe that survived were on nettles, where they were least conspicuous. At St. Helens, in the Isle of Wight, the elimination was 92 per cent on fences where the pupa were conspicuous, as against 57 per cent among nettles where they were inconspicuous.'

92 36

"Dr. C. B. Davenport of the Carnegie Institution for Experimental Evolution placed 300 chickens in an open field. Eighty per cent were white or black and hence conspicuous; 20 per cent were spotted and hence inconspicuous. In a short time twenty-four were killed by crows but only one of the killed was spotted." 37

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Very different results from those just cited are sometimes obtained. Professor Moore writes: "The large tomato worm occurs in two colors, being generally green, almost exactly matching the tomato leaves and stems on which it lives, and more rarely brown and very conspicuous. These caterpillars may be observed to be not infrequently eaten by robins and cuckoos and pecked to death and partially devoured by chipping sparrows. Last summer 34 of these caterpillars were counted on a row of tomato plants. Of these 32 were of the green and only 2 of the brown phrase. . . . Later in the summer the number of these caterpillars was observed to be gradually diminishing until in early September, when they had attained their full growth, the green ones had been reduced to 18, while both of the brown ones remained. Furthermore, it became apparent that no less than 16 of the green caterpillars were parasitized by an ichneumon fly to whose attacks they eventually succumbed, with the net 36 THOMSON, J. A. o. c., p. 200.

87 CHAPIN, F. S. Social Evolution, p. 26.

result that in spite of being protectively colored, out of 32 green caterpillars at the beginning of the season only two a number just equaling that of the unprotected brown caterpillars - survived to pupate pupate with with the latter." 38

It is possible then to overemphasize the value of protective coloration. Other observers lay stress on mimicry, the close resemblance of one animal to another: a fly to a dangerous wasp, a bug to another disliked by birds because of some very disagreeable odor, a moth hardly to be distinguished at rest from a dried leaf. Though it may not be possible to explain all these phenomena or state their meaning they must have some significance. Moreover, we know that some human beings are more likely to take certain diseases than are other persons and to suffer more from them. If the disease results fatally there may come in time the elimination of the susceptible stock. It would seem then that natural selection is a real factor in life even though its whole rôle is not understood and is perhaps exaggerated.

Biology and paleontology have advanced so rapidly that it is now possible to outline the process of evolution. In the earliest of the stratified rocks, the Azoic, there are no signs of life. This does not necessarily mean that no life existed, but that the early forms of life were simple masses without shells or bones which might be preserved. At the bottom of the animal scale are the one-celled forms called protozoa. Of these the ameba (.01 of an inch in diameter) which is common in vinegar, will serve as an illustration. All we can see is a membrane filled with liquid and inclosing a nucleus. The ameba may slowly move by changing its shape. If it comes in contact with

38 MOORE, E. C. In Old Penn. Dec., 1914, p. 361.

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