10 



SCIENCE 



[N. S. Vol. XLI. No. 1044 



living objects with which we deal." Here 

 we almost seem to catch an echo from the 

 utterances of a certain sect of self-styled 

 "scientists" who love to please themselves 

 with the quaint fancy that physical dis- 

 ease is but one of the "errors of mortal 

 mind. ' ' 



Now, it is undoubtedly true that many 

 adaptations, to cite Professor Bateson once 

 more, are "not in practise a very close 

 fit." Even the eye, as Helmholtz long ago 

 taught us, has some defects as an optical 

 instrument; nevertheless, it enables us to 

 see well enough to discern some food for 

 reflection concerning adaptations among 

 living things. And it is my impression that 

 efforts to explain adaptations are likely to 

 continue for the reason that naturalists as 

 a body, perhaps influenced by Huxley's 

 definition of science, have an obstinate habit 

 of clinging to their common sense. 



At the present day there is no longer the 

 smallest doubt of the great outstanding fact 

 that many complex structural adaptations 

 — it would probably be correct to say all 

 such — have not come into existence at a 

 single stroke but have moved forward step 

 by step to the attainment of their full de- 

 gree of perfection. What has dominated 

 the direction and final outcome of such ad- 

 vancing lines? We can not yet answer 

 this question with any degree of assurance ; 

 but procrastinate as we may it must in the 

 end squarely be faced. We have seen one 

 theory after another forced back within 

 narrower lines or crumbling away before 

 the adverse fire of criticism. I will not 

 pause to recount the heavy losses that must 

 be placed to the account of sexual selection, 

 of neo-Lamarckism, of orthogenesis. Some 

 naturalists, no doubt, would assign a promi- 

 nent place in this list of casualties to 

 natural selection; but probably there are 

 none who would hold that it has been de- 

 stroyed utterly. The crux lies in the degree 



of its efficacy. Stated as an irreducible 

 minimum the survival of the fit is an evi- 

 dent fact. Individuals that are unfitted to 

 live, or to reproduce, leave few or no de- 

 scendants — so much, at least, must be ad- 

 mitted by all. But does this colorless and 

 trite conclusion end the matter or ade- 

 quately place before us the significance of 

 the facts? Just here lies the whole issue. 

 Does destruction of the unfit accomplish no 

 other resLilt than to maintain the status quo, 

 or has it conditioned the direction of prog- 

 ress? Accepting the second of these alter- 

 natives, Darwin went so far as to assign to 

 it a leading role among the conditions to 

 which the living world owes its existing 

 configuration. Since his time the aspect of 

 the problem has widely changed. We must 

 rule out the question of the origin of neu- 

 tral or useless traits. We must not con- 

 fuse the evolution of adaptations with the 

 origin of species. We must bear in mind 

 the fact that Darwin often failed to dis- 

 tinguish between non-heritable fluctuations 

 and hereditary mutations of small degree. 

 We are now aware that many apparently 

 new variations may be no more than recom- 

 bination-products of preexisting elements. 

 We should, no doubt, make a larger allow- 

 ance for the role of single "lucky acci- 

 dents" in evolution than did many of the 

 earlier evolutionists. And yet, as far as 

 the essence of the principle is concerned I 

 am bound to make confession of my doubts 

 whether any existing discussion of this 

 problem affords more food for reflection, 

 even to-day, than that contained in the 

 sixth and seventh chapters of the "Origin 

 of Species" and elsewhere in the works of 

 Darwin. 



Undeniably there is a large measure of 

 truth in the contention that natural selec- 

 tion still belongs rather to the philosophy 

 than to the science of biology. In spite 

 of many important experimental and 



