Page:Popular Science Monthly Volume 74.djvu/383

Rh have waltzed for nearly a year. Here are their offspring that show not a trace of the trick.

Cases like these, and I could cite not a few, show how cautiously we must view the theory that such acquired characters are inherited. The experiments do not disprove the possibility, but until direct evidence is forthcoming, judgment must remain suspended.

It has seemed, therefore, to many modern zoologists that we must face the two alternatives, either natural selection or purposeful response. Natural selection has been likened in recent years to a sieve that lets the non-adapted pass through and conserves the adapted. On the sieve metaphor natural selection produces nothing—it is described as a process of destruction of the unfit. How then can natural selection the destroyer become a factor in a creative process?

I have already tried to indicate how natural selection may assume such a rôle. If definite variations appear, however small or large, that are of some benefit, they may engraft themselves in time on to the species; if other useful definite variations are also adding themselves, if their presence insures some further definite variations in the same directions, advance is certain. In other words the elimination of the unfit has not produced the fit, but it has left the conditions more favorable for further progress in the direction of fitness. This is the interpretation of Darwinism that attracts at present the serious attention oi the most thoughtful and advanced students of evolution.

I hesitate to bring before you in a closing sentence or two the alternative doctrine of purposefulness—a doctrine so fraught with human and superhuman import, for of all theories of creation it undoubtedly makes the strongest emotional appeal to mankind.

We are so conversant with the fact in human affairs that whenever purpose is involved there is an intelligent agent—a mind that designs, a mind that foresees—that our thinking has become tinctured with the idea that wherever there is purpose there is something like mind that has anticipated it. Organic nature is full to the brim of what seems purposeful adaptation—means to ends. Two modern zoologists and a noted philosopher have nailed this banner to their mast-head.

There is one consideration above all others that warns the zoologist against speaking dogmatically about purposefulness, or its absence, in the response of living matter to its environment—his ignorance of the causes of variation. If I have implied that all variation is purely "accidental"; if I have led you to infer that it is entirely fortuitous, I have gone beyond the facts. We must be careful to distinguish between the individual differences that we can safely ascribe to chance, and the small definite variations that arise in the germ. The latter appear to be limited, to be in part determined by the internal nature of the parts affected, and to be constant when they have once appeared, but more than this we dare not affirm. We may believe if we like that the evidence