COSMIC PHILOSOPHY 



admitting the full force of the considerations 

 alleged by Mr. Darwin, in his admirable chap- 

 ter on Hybridism, it seems to me that there is 

 a gap at this point which further research will 

 be required to fill.^ As Professor Huxley re- 

 minds us, " it must not be forgotten that the 

 really important fact, so far as the inquiry into 

 the origin of species goes, is that there are such 

 things in nature as groups of animals and of 

 plants, whose members are incapable of fertile 

 union with those of other groups ; and that 

 there are such things as hybrids, which are ab- 

 solutely sterile when crossed with other hybrids. 

 For if such phenomena as these were exhib- 

 ited by only two of those assemblages of living 

 objects, to which the name of species ... is 

 given, it would have to be accounted for by any 



* I doubt if the hypothesis of natural selection, taken alone, 

 will afford the solution of this problem. It seems more likely 

 that such considerations will have to enter as are presented in 

 Mr. Spencer's Principles of Biology ^ vol. i. pp. 209-291. 

 Concerning what may be called the ** dynamics of heredity,'* 

 we know as yet but little ; but as far as speculation has already 

 gone, Mr. Darwin's theory of pangenesis seems to me decid- 

 edly inferior to Mr. Spencer's theory of physiological units. I 

 do not discuss these theories here, because it is not necessary 

 for the general purposes of this work. It may do no harm, 

 however, to remind some of my readers that ** pangenesis " is 

 merely a subsidiary hypothesis, with the possible inadequacy 

 of which Mr. Darwin's main theory is in no way con- 

 cerned. 



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