396 THE POPULAR SCIENCE MONTHLY. 



two lines of thinkers or artists, then the general truth of this principle 

 is abundantly clear. 



Supposing such small functionally - produced modifications to be 

 always taking place, it will be obvious that they must take place 

 most in the most differentiated societies, and least in the least differ- 

 entiated. A race of hunting savages will perform a certain number 

 of routine acts, which will be for the most part the same for all mem- 

 bers of the tribe, and will remain pretty much the same from genera- 

 tion to generation. In the particular direction of hunting and fishing, 

 the cleverness . at last attained will be very remarkable ; but in most 

 other directions there will be little excellence and still less variety. 

 On the other hand, in a tribe which is also made a trading and navi- 

 gating one by the accident of a maritime position, a new set of activi- 

 ties will be specially cultivated, and will give rise to new functional 

 modifications in a different direction. Suppose some of the tribe, in 

 this latter case, to be mainly inland cultivators and hunters, while 

 others of the tribe are mainly seaboard traders or pirates, then each 

 of these sections will tend to develop certain special hereditary brain- 

 modifications of its own. But if a man of the inland section marries 

 a woman of the maritime section, or vice versa, then the offspring will 

 tend to reproduce more or less the structural peculiarities of both 

 parents. And here comes in an important corollary. For though, 

 under such circumstances, the children may none of them fully repro- 

 duce all the brain-gains of their father's line, nor all the brain-gains 

 of their mother's line, they will yet on the average reproduce a fair 

 share of the former and a fair share of the latter. Accordingly, they 

 will usually turn out, on the whole, persons of higher general brain- 

 power than either ancestral series ; they will partially unite the strong 

 points of both. 



It seems to me that this principle is one of very great importance. 

 From it we can deduce the conclusion that in any complex society 

 many children represent directly a convergence of two unlike lines of 

 descent, and indirectly a convergence of innumerable unlike lines, with 

 corresponding gain to the species. Two parents, possessing distinct 

 points of advantage of their own, produce children, some of whom 

 resemble rather the one, and some the other ; but many of whom will 

 at least tend to resemble both in their stronger points. Of course, one 

 must allow much for the idiosyncrasis as well as for the crasis. This 

 child may fall below both its parents in most things ; that child may 

 reproduce the weakest elements of both ; yonder other child may at- 

 tain the average or may surpass them in everything. But, on the 

 whole, the principle of convergence seems to imply that in a fairly 

 complex society there will always be an average of mental improve- 

 ment from generation to generation, due to the constant intercrossing 

 of brains specially improved in particular directions. This improve- 

 ment will, it need hardly be said, be increased and favored by natural 



