18 SOCIAL EVOLUTION 



is 9 cm. taller than the average in<li\ idual, then we 

 may expect the child to be one-third of 9 cm., or 3 cm., 

 above the average. It will thus be seen that if both 

 parents differ in the same direction from the average, 

 the effect of both will be cumulative ; and if both differ 

 from the average of their people by the same amount, 

 the joint effect of the two parents may be expressed by 

 the coefficient of about two-thirds. In case, for instance, 

 both father and mother should be 9 cm. above the type 

 average, we should expect the child to be about two-thinls 

 of 9 cm., or 6 cm., above the average." 18 



These variations, inherited in accordance with the laws 

 that have been outlined, form what Professor Thomson 

 has called the "raw materials" of evolution. Of the 

 origin of these variations we know little. In the micro- 

 cosm of the germ cells there goes on a process of extra- 

 ordinarily intricate permutation and combination. 

 Weismann supposes that there is a struggle within the 

 germ cell between rival hereditary items. However this 

 may be, there is much research still necessary before we 

 can hope to speak in dogmatic fashion of the origin of 

 variations. 



SUPPLEMENTARY READINGS. 



BOAS, F. The Mind of Primitive Man. 

 CRAMPTON, H. E. The Doctrine of Evolution. 

 DARWIN, C. The Origin of Species. 

 DAVENPORT, C. B. Heredity in Relation to Eugenics. 

 GALTON, F. Natural Inheritance. 



Ki LLICOTT, W. E. The Social Direction of Human Evolution. 

 METCALF, M. M. Organic Evolution. 

 PUNNETT, R. C. Mendelism. 



ROMANES, G. J. Darwin and After Darwin, I The Darwinian 

 Theory. 



i* Boas, op. ctf., p. 82. 



