The Wallace-Darwin Correspondence 



Is the orang polygamous ? But I daresay I shall fiud 

 that in your papers in (I think) the Annals and Magazine 

 of Natural History, 



The following group of letters deals with the causes of 

 the sterility of hybrids (see note in ^^ More Letters/' p. 

 287). Darwin's final view is given in the '^ Origin," 6th 

 edit., 1900, p. 384. He acknowledges that it would be 

 advantageous to two incipient species if, by physiological 

 isolation due to mutual sterility, they could be kept from 

 blending; but he continues: ^' After mature reflection, it 

 seems to me that this could not have been effected through 

 Natural Selection." And finally he concludes (p. 386) : 

 ** But it would be superfluous to discuss this question in 

 detail; for with plants we have conclusive evidence that 

 the sterility of crossed species must be due to some 

 principle quite independent of Natural Selection. Both 

 Gartner and Kolreuter have proved that in genera includ- 

 ing numerous species a series can be formed from species 

 which, when crossed, yield fewer and fewer seeds, to 

 species which never produce a single seed, but yet are 

 affected by the pollen of certain other species, for the 

 germen swells. It is here manifestly impossible to select 

 the more sterile individuals, which have already ceased 

 to yield seeds; so that this acme of sterility, when the 

 germen alone is affected, cannot have been gained through 

 selection; and from the laws governing the various grades 

 of sterility being so uniform throughout the animal and 

 vegetable kingdoms, we may infer that the cause, what- 

 ever it may be, is the same or nearly the same in all 

 cases." 



Wallace still adhered to his view {see '^ Darwinism," 

 1889, p. 174, also p. 292 of " More Letters," note 1, and Letter 

 211, p. 299). The discussion of 1868 began with a letter 

 from Wallace, written towards the end of February, giving 

 his opinion on the ** Variation of Animals and Plants " ; 

 the discussion on the sterility of hybrids is at p. 185, Vol. 

 II., 1st edit. 



195 



