Recent Biology 375 



What the two have in common is the postulate of infertility, Ro- 

 manes assuming its segregation value, and so finding it available 

 to produce divergent, or as he calls it ' polytypic,' evolution. 



The other point of which Romanes makes so much — and, I 

 think, unfortunately — is that in which he agrees with the Rev. 

 Mr. Gulick, the writer who first proposed and has elaborately 

 expounded — but under different terms — the principle of 

 physiological selection. Both of these authors, Romanes later 

 so far as one can gather, formulated the general principle of 

 ' Isolation ' ; meaning by it — to gather the matter up briefly — 

 any sort of relative control of pairing. If, for any reason, males 

 A to Z can pair with females a to /, but cannot pair with females 

 m to z, these males are then ' isolated ' from the latter females. 

 Under this 'principle,' on the author's showing, everything 'in 

 heaven above and on earth beneath ' can be brought. Natural 

 selection is only a case of isolation ; so is the migration of 

 Wagner, and the geographical separation of Weismann, and 

 physiological selection from infertility, and artificial, and indeed 

 sexual selection. He says : " Equalled only in its importance by 

 the two basal principles of heredity and variation, this principle 

 constitutes the third pillar of a tripod on which is reared the 

 whole superstructure of organic evolution " (p. 2). With all 

 the laboured proof of this proposition, it suffices to say that it is 

 true, because self-evident ; and at the same time, in the present 

 state of biological science, well-nigh worthless. For the very 

 concept of heredity through sexual reproduction presupposes 

 it. All heredity m particular involves the ' isolation ' of the two 

 parents temporarily for the purposes of the act of mating. We 

 might even go so far as to announce a great ' principle of 

 negative isolation ' (!), ?>., that by artificial selection, or any sort 

 of human regulation, the upper limit to the birth-rate in any 

 species may be set by the isolation of the male from more than 

 one mate. Surely it adds nothing to natural selection to call 

 it also isolation, explaining that it depends upon the elimina- 

 tion of some individuals and the consequent isolation of those 

 not banished to the shades ; nor does it add anything to the 

 other sorts of selection, now historic both as facts and as having 



