1890 PHYSIOLOGICAL SELECTION 177 



at least, the chief condition) instead of the result of 

 specific differentiation. This is just the opposite view 

 to that now held by all evolutionists, and, I believe, 

 by Darwin himself. (See ' Origin,' pp. 245-246 ; 

 1 Variation,' ii. pp. 171-175.) Now, if this view be 

 sound, my theory is obviously not restricted to any 

 one class of causes that may induce mutual sterility. 

 Such cases may be either extrinsic or intrinsic as 

 regards the reproductive system ; they may be either 

 direct in their action on that system or indirect (e.g. 

 natural selection, or use and disuse, &c., producing 

 morphological changes elsewhere, which in turn react 

 on that system) ; therefore these causes may act 

 either on a few or on many individuals. Yet Wallace 

 does not seem to see this, but argues in the ' Fort- 

 nightly ' that they can only act on an individual here 

 and there. 



I sincerely hope you will give your attention to 

 the subject, because the great danger I now fear is 

 prejudice against the theory on account of people not 



taking the trouble to understand it. How absurd , 



for example, giving that quotation from ' Origin ' in 

 1 Nature,' as evidence of Mr. Darwin's having con- 

 sidered the theory! Bead with its context, the pas- 

 sage is arguing (much against the writer's desire) that 

 variations in the way of sterility with parent forms 

 cannot be seized upon (or perpetuated as specific dis- 

 tinctions) by natural selection. But physiological 

 selection says that such variations do not require to be 

 seized upon by natural selection. Therefore, so far as 

 the passage in question proves anything, it tends to 

 show that nothing could have been further from the 



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