CHAPTER V 
THE INHERITANCE OF MENTAL ABILITY 
“We inherit our parents’ tempers, our parents’ conscientiousness, 
shyness, and ability, as we inherit their stature, forearm, and span.” — 
Karl Pearson. 
WE have seen that feeble-mindedness and other forms of 
mental defect tend to be strongly transmitted. Can it be shown 
that the same statement applies to superior ability? For various 
reasons the doctrine that mental traits are inherited has been 
regarded with suspicion, and has frequently encountered active 
opposition. Many writers, influenced by a theological or meta- 
physical bias, have been reluctant to admit that the laws of 
heredity which apply to the transmission of physical traits hold 
also for the mind. Many political and social theorists have found 
it convenient to minimize the importance of the innate mental 
differences between men, and have attempted to explain such 
mental differences as were only too obvious as the result of 
accidents of education, early experience, and other circumstances 
external to the individual himself. The doctrine of the equality of 
man preached by Rousseau and his followers and embodied in our 
own Declaration of Independence had a tendency to prevent due 
recognition of the fact that human beings differ profoundly in 
their inherited mental gifts. The admission of such inheritance 
might prove a dangerous concession to the claims of aristocracy, 
and it is not surprising, therefore, to find such a champion of 
popular rights as Thomas Paine contending against the possi- 
bility of the inheritance of mental ability. Writers of a much 
later period, though inspired by much the same motives, have 
expressed similar views. Henry George, who, like many other 
socialists, attempted to explain the differences among men as 
chiefly the production of an iniquitous social order, stated that 
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