310 THE INDUCTIONS OF BIOLOGY. 



sporting dogs which spontaneously adopted in the field, certain 

 modes of behaviour which their parents had learnt. 



But the best examples of inherited modifications produced 

 by modifications of function, occur in mankind. To no 

 other cause can be ascribed the rapid metamorphoses under- 

 gone by the British races when placed in new conditions. 

 In the United States the descendants of the immigrant Irish 

 lose their Celtic aspect, and become Americanized. This 

 cannot be ascribed to mixture, since the feeling with which 

 Irish are regarded by Americans prevents any considerable 

 amount of intermarriage. Equally marked is the case of the 

 immigrant Germans who, though they keep very much apart, 

 rapidly assume the prevailing type. To say that " spon- 

 taneous variation " increased by natural selection, can have 

 produced this effect, is going too far. Peoples so numerous 

 cannot have been supplanted in the course of two or three 

 generations by varieties springing from them. Hence the 

 implication is that physical and social conditions have 

 wrought modifications of function and structure, which off- 

 spring have inherited and increased. Similarly with special 

 cases. In the Cydopcedia of Practical Medicine, Vol. II., p. 

 419, Dr. Brown states that he " has in many instances ob- 

 served in the case of individuals whose complexion and 

 general appearance has been modified by residence in hot 

 climates, that children born to them subsequently to such 

 residence, have resembled them rather in their acquired than 

 primary mien." 



Some visible modifications of organs caused by changes in 

 their functions, may be noted. That large hands are inherited 

 by those whose ancestors led laborious lives, and that those 

 descended from ancestors unused to manual labour com- 

 monly have small hands, are established opinions. It seems 

 very unlikely that in the absence of any such connexion, 

 the size of the hand should have come to be generally re- 

 garded as some index of extraction. That there exists a like 

 relation between habitual use of the feet and largeness of the 



