THE REPRODUCTIVE EACTOR IN EVOLUTION. 283 



physiological barrier, just as they might be insulated by a geographical 

 one, and left free to develop along divergent paths of their own. Here 

 again there is recognition of the reproductive factor in evolution; but 

 how far, and in what cases species have so originated, is obviously a 

 question which would involve discussion of each individual instance. 



(d~) Worthy of reiteration is the suggestion of Robert Chambers, 

 crudely illustrated as it may_have been, that environmental influences 

 acted with special power upon the generative system, and that the 

 prolongation of gestation was a maternal sacrifice which brought its 

 own reward in the higher evolution of the offspring. Miss Buckley, 

 along a similar line of thought, has well pointed out how the increase 

 of parental care was a factor in, as well as a result of, the general 

 ascent; how the success of birds and mammals especially must in part 

 be interpreted in reference to the noteworthy deepening of parental 

 affection, and strengthening of the organic and emotional links between 

 mother and offspring. In emphasizing the progressive value of pro- 

 longed infancy, especially in the evolution of the emotions, Fiske has 

 also recognized the importance of the reproductive factor. 



III. Further Construction. — The general tendency of all theo- 

 ries of evolution has been to start with the individual organism as the (T^ 

 unit, and to consider the self-maintaining and nutritive activities as 

 primary, the reproductive and species-regarding as only secondary. 

 But along many lines of research, such as those indicated in the pre- 

 ceding paragraph, the importance of the reproductive factor has been 

 recognized, and the center of gravity of the evolutionary inquiry has 

 already been to some degree shifted. Recent investigations on 

 heredity, for instance, forbid that attention should any longer be 

 concentrated on the individual type, or reproduction regarded as a 

 mere repetition process; the living continuity of the species is seen 

 to be of more importance than the individualities of the separate 

 links. Physiologists and evolutionists are coming to see the most 

 complex individual lives, in Foster's phrase, as "but the bye-play 

 of ovum-bearing organisms." The species is a continuous undying 

 chain of unicelluar reproductive units, which indeed build out of and 

 around themselves transient multicellular bodies, but the processes of 

 nutritive differentiation, and other individual developments, are 

 secondary, not primary. 



Thus it is the central generalization of botany that, despite the 

 individual differentiation of fern, selaginella, cycad, conifer, and flower, 

 these turn out on deepest analysis, to be but the surviving phases of 

 a continuous and definite increase in the subordination of the sexual 

 parents to their asexual offspring (see pp. 185, 195). 



