15 



Danger of 



Declining Intelligence 



At the human plane in the evolution of intelligence nature 

 exhibits a very uneven product. So great are the differences 

 in mental level between the lowest and the highest individ- 

 uals in our population, and so large are the numbers of in- 

 dividuals at low or middle levels that some students of our 

 civilization consider this a most menacing situation, espe- 

 cially in those societies where a differential birth rate seems 

 to be working against the upper mental groups. The dif- 

 ferential birth rate referred to is the possibility of an exces- 

 sive reproduction at lower levels of intelligence and a failure 

 of the peoples of the highest intelligence to reproduce even 

 at group replacement rates, to the extent that in future gen- 

 erations the general average of intelligence might be danger- 

 ously lowered. Along with overpopulation, adverse differ- 

 ential reproduction could be a fatal trend in man's future 

 evolution, a trend leading him eventually into an intellectual 

 and social blind alley. 



It appears from the evidence now available that among 

 the peoples of the world the upper heritage of intelligence, 

 the heritage of gifted individuals so necessary to the scien- 

 tific and technological structure of our civilization, is be- 

 coming thinner and thinner. How few the individuals of 

 high intellect can become in proportion to the population 

 as a whole and still permit advances in, or even hold, the 



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