Initiative in Evolution

by Walter Kidd

The Problems Considered.

It seems but natural to most persons who contemplate with any care the ever-changing and progressive drama of life in plants and animals that unquestionably the dramatis personæ by their individual response to the environments and exercise of their functions must contribute a share, however small, to their offspring. When first this view presents itself to their minds they resent as “unnatural” any other possibility. But, alas! they find that such a conclusion is not permitted in those regions where alone the white light of science shines. Here the writ of a priori does not run. The spirit of inquiry makes its challenge to every presupposi­tion and every assertion in its province—even those of current science. I have shown that this particular assump­tion of the natural man was firmly challenged by Weismann, who was not the first, but the greatest, biologist to teach that modifications are not transmitted. Accordingly, agreeable and convenient as it would be to assume the Lamarckian hypothesis as a working one, it needs in the present day to be supported by evidence before this can be allowed. Facts, then, against Weismann’s dogma are demanded and of such a kind as will satisfy so powerful an advocate of his own views. In passing it may be remarked again that there is nothing so misleading as facts, except statistics, and for both sides to bear in mind the warning of a French writer that in such inquiries as this we should be careful lest we find the facts for which we are looking.

To meet the conditions laid down in Professor Thomson’s Canon I propose to describe certain phenomena which are adduced as instances of modifications in certain mammals whose structure and mode of life are intimately known, and whose ancestry is little in dispute.[33] The most convincing of these lines of evidence are those which are shown to be outside the range of any form of selection, as well as the distributional factors of Mendel and de Vries. It is well to enumerate here the six different factors in organic evolution which might claim a share in the produc­tion of such humble phenomena as form the subject-matter of this volume—they are:

1. Personal Selection of Darwin.
2. Sexual Selection.
3. Histonal or Cellular Selection of Roux.
4. Germinal Selection.
5. Inheritance according to Mendelian principles.
6. Inheritance of Mutations.

There is a somewhat severe and ill-defined condition attached to the formula in question for it demands that such modifications as will satisfy the neo-Darwinians shall not be correlated with any useful character.[34] If such a conditio sine quâ non were taken too literally it would at once foreclose the case as to the possibility of transmission of modifications at all, the questions of issue ought in that case never to have been raised—and, cadit quæstio. This cannot be the intention of the biologist who propounds the formula. It could not reasonably be carried so far as to insist that a modifica­tion arising from a certain habit, active or passive, in an animal, and which on that account, and on paper, may loosely be said to be ‘correlated’ with it, is to be ruled out. That would be tantamount to saying for example, that, because an animal must lie down in a certain attitude when it rests, or walk or run in a certain manner, in other words that it is useful to exist, certain modifications claimed to be due to these fundamental parts of existence must be excluded from the inquiry. The neo-Darwinian is not a critic easy to be entreated, but that he would not claim. Let me take one example of what I mean. A short-haired dog will spend a considerable part of its daily life, and presumably a long line of ancestors did so too, lying with its forelegs planted in front of its chest and its head either raised in the air when awake or resting on the upper surface of the forelegs (of course the familiar attitude of a dog with its body and head curled up and fore-legs doubled is not referred to here). If the hairy coat be examined over its neck and jaw, which lie in this attitude, on and against the forelegs, a remarkable reversal of the direction of the hairs is found and the outline of this forms an accurate mould of the surface applied to the forelegs. This is transmitted of course from previous generations of domestic dogs. A precisely analogous reversal of the hairs is found on the under or extensor surfaces of the forelegs, matching with wonderful exactness the area of pressure of these on the ground, and anyone can see it who has a canine friend of the fox-terrier type. Long-haired dogs display it less neatly outlined. An instance such as this cannot be excluded from the evidence forthcoming because it is correlated with the useful “character” of lying in a certain attitude. Such a phenomenon, many similar to which will be seen later, had at any rate an origin de novo at some time in the ancestral stock, and in some way. To discover these is part of my business. The boldest neo-Darwinian will not claim that this arrangement of a dog’s hair arose by selectional processes within the germ either in the initial or completed stages.