FOR DARWIN 379 



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 evi- 

 dence 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 re- 

 sponse. 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 role. 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 favor- 

 able for further progress in the direction of fitnes^. This is the inter- 

 pretation 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 alter- 

 native 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 afiirm. We may believe if we like that the evidence 



