SEGREGATION. 489 



among groups o inferior creatures. The human races tend 

 to differentiate and integrate, as do races of other living 

 forms. Of the forces which effect and maintain the 



segregations of mankind, may first be named those external 

 ones which we class as physical conditions. The climate and 

 food that are favourable to an indigenous people, are more 

 or less detrimental to a people of different bodily constitu- 

 tion, coming from a remote part of the Earth. In tropical 

 regions the northern races cannot permanently exist : if not 

 killed off in the first generation, they are so in the second; 

 and, as in India, can maintain their footing only by the 

 artificial process of continuous immigration and emigration. 

 That is to say, the external forces acting equally on the in- 

 habitants of a given locality, tend to expel all who are not 

 of a certain type ; and so to keep up the integration of those 

 who are of that type. Though elsewhere, as among Euro- 

 pean nations, we see a certain amount of permanent inter- 

 mixture, otherwise brought about, we still see that this takes 

 place between races of not very different types, that are 

 naturalized to not very different conditions. The 



other forces conspiring to produce these national segrega- 

 tions, are those mental ones which show themselves in the 

 affinities of men for others like themselves. Emigrants 

 usually desire to get back among their own people; and 

 where their desire does not take effect, it is only because the 

 restraining ties are too great. Units of one society who 

 are obliged to reside in another, very generally form colo- 

 nies in the midst of that other small societies of their 

 own. Races which have been artificially severed, show 

 strong tendencies to re-unite. Now though these segrega- 

 tions that result from the mutual affinities of kindred men, 

 do not seem interpretable as illustrations of the general 

 principle above enunciated, they really are thus interpret- 

 able. When treating of the direction of motion ( 80), 

 it was shown that the actions performed by men for the 

 satisfaction of their wants, were always motions along lines 

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