Natural Selection Still Unproved 127 



agency or combination of agencies, had a share in the 

 process. All naturalists are now agreed that, as a 

 matter of historical fact, it was the propounding of 

 natural selection by Darwin that led to the acceptance 

 of evolution, to the fact that evolution " takes its place 

 alongside of those accepted truths which must be 

 reckoned with by philosophers of all schools." The 

 difficulty as to natural selection still exists, and there 

 is no better way to express it than in Huxley's words, 

 written in the early sixties : 



" But, for all this, our acceptance of the Darwinian hypothesis 

 must be provisional so long as one link in the chain of evidence 

 is wanting ; and, so long as all the animals and plants certainly 

 produced by selective breeding from a common stock are 

 fertile with one another, that link will be wanting ; for, so 

 long, selective breeding will not be proved to be competent to 

 do all that is required of it to produce natural species. ... I 

 adopt Mr. Darwin's hypothesis, therefore, subject to the pro- 

 duction of proof that physiological species may be produced by 

 selective breeding ; just as a physical philosopher may accept 

 the undulatory theory of light, subject to the proof of the ex- 

 istence of the hypothetical ether ; or as the chemist adopts the 

 atomic theory, subject to the proof of the existence of atoms ; 

 and for exactly the same reasons, namel)', that it has an im- 

 mense amount of prima facie probability ; that it is the only 

 means at present within reach of reducing the chaos of observed 

 facts to order ; and, lastly, that it is the most powerful instru- 

 ment of investigation which has been presented to the natural- 

 ists since the invention of the natural system of classification, 

 and the commencement of the systematic study of embryology." 

 — Man's Place in Nature, p. 149.* 



* Further details on the subject of this chapter may be ob- 

 tained in Clodd's excellent volume. Pioneers of Evoliition , 

 where an account of the history of the idea of evolution from 

 the earliest times is given ; and in Poulton's Charles Darivin 

 and the Theory of Natural Selection, where there is a particu- 

 larly valuable chapter upon Huxley's relation to Darwinism. 



