DIMINISHING ENVIRONMENTAL INFLUENCE 315 



such modifications as are known to occur within the individual life at 

 any time from conception to death or within a single generation. This 

 will throw out of the question a hoard of cases where it is not quite 

 clear whether the observed changes are the result of direct modification, 

 in the true restricted sense, or are perhaps due in part to accumulated 

 influences acting through several generations. 



Confining ourselves then to a discussion of modification in the 

 strict sense of the term, let us briefly survey the conclusions of experi- 

 mental zoology, embryology and botany, and also experiments on 

 regeneration, to see what lesson may be learned from the results of all 

 this painstaking work. It will be of course impossible to treat of more 

 than a fraction of the multitudinous results which have already been 

 handed in as contributions to this young and rapidly growing branch 

 of knowledge — experimental biology; but I believe that even a super- 

 ficial survey will suffice to bring out my general contention. 



The fact that ordinary differences in human environment, as shown 

 in the history of royalty, appeared to alter the innate character and 

 capacity for achievement but little, together with the fact that experi- 

 mentally a great deal in the way of modification could be produced in 

 the domains of zoology and botany, led me to suppose that there must 

 be some inherent biological differences rendering tissues low in the 

 organic scale especially susceptible to the molding of external influences. 



This idea I advanced as an hypothesis in 1906 in the following 

 words : x 



Among plants and the lower forms of animals, especially the invertebrates, 

 many experiments have shown the remarkable changes which may be directly 

 induced by changes in the outward conditions of life. These are in general the 

 more striking the lower we go in the scale of organic evolution, so that it may 

 well be that in the highest attributes, namely, mental or moral, we can expect 

 the least results from outward forces. This hypothesis may prove a veritable 

 generalization throughout the animal series. 



In 1908 2 I expressed the same idea in the following passage: 



The profound modifications that may be induced in plants and the inverte- 

 brates by alterations of the surroundings are well known. But when one takes 

 a survey of this whole question of modification, one sees that in general the 

 lower we go in the scale of life the easier it is to effect the changes. It is 

 significant that among vertebrates the modifications are largely associated with 

 the integument, where cell-division is active and constant, and in a tissue that 

 is not highly organized. 



It is to offer the proof for this generalization that I now propose a 

 survey of the whole question. 



1 " Mental and Moral Heredity in Royalty," New York, Henry Holt & Co., 

 1906, p. 294. 



2 Vol. V. American Breeders Association, Report of the Committee on 

 Eugenics, p. 248. 



