482 POPULAR SCIENCE MONTHLY. 



agencies which, cause " sports " are the real causes of the muta- 

 bility of species, and natural selection can do nothing more than 

 to exterminate disadvantageous sports, and thus favor advanta- 

 geous ones. 



The "organic stability" to which so much is attributed is 

 held to be due to the fact that the child inherits in part from its 

 parents, in part from more remote ancestors ; and since the sum 

 of its ancestry, or its " mid-parentage," is on the average nearer 

 than any exceptional parents to the mean of the race, the children 

 of selected parents are on the average more mediocre than their 

 parents. 



It is quite possible that Gal ton's data may be valuable and 

 trustworthy, and that they may yet fail to prove this generali- 

 zation ; and I shall try to show that this is the case, although I 

 am not sure that I fully grasp his point of view. 



I assume that he regards a zoological type or species as some- 

 thing ; something which is due to a " principle of stability," 

 which is not the result of selection. This is assuredly the cur- 

 rent interpretation of his statements, and it is from this stand- 

 point that I shall examine his writings. 



If this is not his opinion ; if he really believes that this " prin- 

 ciple" owes its existence to past selection; if he only deduces 

 from his data the generalization that the results of past selection 

 may persist after it has ceased to act ; I see no ground for criti- 

 cism, for his data assuredly prove this much, although I can not 

 reconcile his statement that " the principle of stability is inde- 

 pendent of selection " with the belief that it is the result of past 

 selection. 



Before entering upon the discussion of the subject it may be 

 well to ask what evidence there is that the child does inherit from 

 any ancestor except its parents, for descent from a long line of an- 

 cestors is not necessarily equivalent to inheritance from them, 

 and it is quite possible that the conception of a " mid-parent " 

 may be nothing but a logical abstraction. 



Most of its support is derived from the phenomena of reversion 

 or atavism ; from the appearance in children of ancestral features 

 which were not exhibited by the parents. While these phenome- 

 na are familiar and real, we may well doubt whether any of them 

 are reversions in Galton's sense. 



In some cases we can prove that a so-called reversion is 

 simply the manifestation of a feature which is latent in the 

 structure of all the normal individuals of the species. The 

 occurrence of a distinct premaxillary bone in man is an exam- 

 ple of this sort of reversion. It is the outcome of the arrest of 

 normal development, and this arrest might have happened to 

 any member of the species. We do not know what causes the 



