248 A STUDY IN HEREDITY 



quarter from the grandparents, one-eighth from the great-grand- 

 parents, and so on. Were such theories true, there could be no 

 retrogression except through reversed selection, for the more 

 evolved ancestors would forever tend to make their influence felt. 

 But, plainly, retrogression occurs in the mere absence of selection. 

 Moreover, if it be true that the organic world has arisen through 

 the preservation and accentuation of favourable variations, and if 

 it also be true that ontogeny is a recapitulation of phylogeny, 

 then it seems to me that it must be further true that there is 

 necessarily a greater tendency towards retrogression than towards 

 evolution. For all atavistic variations must tend towards retro- 

 gression ; whereas all evolutionary variations need not constitute 

 extensions of the previous evolution. They may result in 

 divergencies in new directions, or may even constitute reversals 

 of the previous evolution, as in those cases of which Reverse Selec- 

 tion takes advantage. Given sufficient time, in the absence of 

 selection, retrogression must therefore necessarily ensue. 



The rationale of retrogression, I take it, is as follows : — 

 Suppose, as regards any character which has undergone evolution, 

 that A, B, C, D represent a line of individuals ; then if D reverts 

 to B — that is if D varies from his parent C in such a way that in 

 his ontogeny he represents the life-history of the race only up to 

 the point reached by B, omitting the additional characteristics of 

 C — it is evident, from the point of view of heredity, that the series 

 becomes A, B, D, or, rather, it becomes A, B, since, in effect, D 

 is B. C then disappears completely and forever from the series, 

 and it follows that, if the characters of C ever reappear in E, or 

 any subsequent member of the series, they must do so as a result 

 of fresh evolution, not as a result of reversion. It is necessary to 

 emphasise this point, for on it my whole argument depends. If 

 D, on the other hand, varies in such a manner from C that, afler 

 representing C, that is, after recapitulating the whole of the 

 phylogeny, he reverts back to B, then C does not disappear from 

 the series. C will still be represented in the ontogeny, and, if 

 his characteristics reappear in any individual at the end of the 

 ontogeny, that is in the adult, it will be as a result, not of 



