252 EFFECTS OF SEXUAL REPRODUCTION. 



growth due to a college education, then the offspring would have 

 an unusual increase of brain size, which would be transmitted to 

 the next generation. If this last transmission occurs at an early 

 age we would have a large brain with small brain power. On 

 the other hand, if a person whose brain ceased to grow at the age 

 of twenty and who accumulated considerable brain power late in 

 life after the brain had ceased to grow, should have a child in 

 mature years, then this child would inherit considerable mental 

 power and relatively small cranial capacity. We may see an illus- 

 tration of this in the case of the Incas, whose cranial capacity was 

 small, but who were comparatively high in the scale of civilization. 

 The education of their children was limited to that of their fathers, 

 but their marriageable age did not come till from 24 to 26. 3 



INHERITANCE AT CERTAIN AGES. 



Darwin has shown that characters which appear at certain ages 

 in the parent tend to reappear in the offspring at corresponding 

 ages, and he adds the statement that when there are deviations 

 from this rule the tendency appears to be for them to occur earlier 

 rather than later in the offspring. The rule of uniformity that 

 causes the reappearance of characters in offspring at ages corre- 

 sponding to those in which they appeared in the parent, relates to 

 those characters which are not affected by use and disuse, while 

 characters which are stimulated and developed by long continued 

 functional activity appear earlier and characters which are degen- 

 erated by disuse appear later. The general rule relating to func- 

 tionally developed characters appears to be that each fertilized germ 

 starts upon its career of development with an initial velocity which 

 would bring it, at the normal age of physical maturity, to a con- 



(3) Latourneau, Evolution of Marriage, p. 174. 



