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, i^ansies, eels or ele- 

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

 is possible to measure these differences. These "ob- 

 served ditferences" 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.^ These variations are congenital, not made. 

 They are often distinct at birth. They are in many 

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

 been called the raw material of evolution. 



The study and organization of facts bearing upon varia- 

 tion have disclosed that there are two different types of 

 variation. The first, is known as fluctuating or continu- 

 ous variation ; in w^hich the divergence from the parental 

 character is relatively slight. The second, is known as 

 stable or discontinuous^ variation ; in which there is great 

 divergence from the parental character. Some biologists 

 consider the first non-hereditary, the second hereditary. 



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 ran- 

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



5 Thomson & Geddes, op. cit., pp. llG-117. c Metcalf, op. dt., p. 10. 



