Page:Popular Science Monthly Volume 77.djvu/173

Rh of specimens of the pure, native stock be properly preserved in our museums, for future comparison.

I wish here to register an objection to the prevalent idea that experimental methods upon the higher animals under artificially imposed conditions may be expected to lead invariably to the satisfactory solution of evolutionary problems. I have in mind some experiments recently made upon birds. Certain species were kept captive in enclosures in which a relatively high atmospheric humidity was maintained. The experimenter found that within the life of an individual, in fact within a few months, successive molts resulted in the plumages of some of the birds becoming darker. Feathers which were normally marked lightly with black became solid black. The increase of pigment throughout the plumage brought about a conspicuous change in the appearances of the birds, as great a difference as one finds between two near-related species under natural conditions, the one occupying an area of arid climate, the other a region of humidity.

The conclusion from these few experiments, quite generally, but, I feel confident, too hastily, drawn, has been that there may be a "direct influence" of the atmospheric humidity sufficient to bring about the color characters of the different species as we find them under the varying natural conditions; in other words, that it is not a matter of gradual adaptive acquisition subject to inheritance. It is even being maintained widely among biologists that natural selection may have very little to do with the characters of animals as we find them in nature.

I believe that the above experiments, among others carried on in the same way, will, alone, lead to inductions largely inapplicable to animals in the wild. My chief objection is that wild animals brought into confinement at once begin to show irregularities in various structural respects. This is shown sufficiently by studies upon the skeletons of animals dying in zoological parks, a very large proportion of which are abnormally modified in various particulars. This diseased condition undoubtedly begins just as soon as the animal is taken out of its natural surroundings. For the cessation of any one set of muscular activities is bound to bring about immediate changes in quantitative metabolism in the system. Change in food supply directly affects the entire organism, and unusual invasion by parasites ensues with concomitant irregular growths. How then can we expect to get a knowledge of the processes of species formation under natural conditions from the extraordinary physical development or behavior of such animals?

I would urge that it is only through the close and long-continued study of animals in the wild state, that is, under perfectly natural conditions, that we can hope to gather conclusive evidence as to the