6 SOCIAL EVOLUTION 



beget like should now be clear. It is the continuity of 

 the germ-plasm. 



When one compares a number of members of the same 

 species, whether men, hens, dogs, pansies, eels or ele- 

 phants, he finds that they differ from one another. It 

 is possible to measure these differences. These "ob- 

 served differences" may be due to many things. Many 

 of them may be involved with sex, and thus accounted 

 for; some, with age; others may be due to the influence 

 of surroundings in early plastic years, for example, the 

 twisted twig and the bent limb. These last are changes in 

 the bodies of plants and animals which are acquired ; they 

 are modifications, not inborn. When from the total ob- 

 served differences, these peculiarities of sex, age, and 

 modification are subtracted, a very interesting remain- 

 der is left, which we define as inborn or germinal varia- 

 tions. 5 These variations are congenital, not made. 

 They are often distinct at birth. They are in many 

 cases, if not always, transmissible. They form what has 

 been called the raw material of evolution. 



In late years a quantity of facts bearing upon varia- 

 tions has been gathered. The study and organization 

 of this material has shown that there are probably two 

 quite distinct types of variation : first, fluctuating or con- 

 tinuous variation, producing comparatively slight diver- 

 gence from the parental character; and second, stable 

 or discontinuous variation, producing generally great 

 divergence from the parental type. 6 



Fluctuating or continuous variation may be illustrated 

 as follows: from the registration of variations that 

 occur in the height of a large number of men taken at 

 random, it was found that there was a proportion be- 



o Thomson & Geddes, op. cit., pp. 115-116. Metcalf, op. cit., p. 10. 



