41 8 READINGS IN BIOLOGICAL SCIENCE 



The sum total of their research fills innumerable volumes. But much of this 

 research has been badly done, as would be expected in so new and difficult 

 afield. 



There is still controversy among psychologists; part of this may be de- 

 scribed as a controversy between older schools of psychologists and those 

 trained during the last decade. Laymen who engage in controversy are 

 often found to be leveling their lances against concepts and methods that 

 have been completely discarded by critical contemporary psychologists. 

 Much of this controversy relates to the roles of heredity and environment 

 in the development of intelligence. Recent work goes far to clarify this dif- 

 ficult field. In the past few years, the so-called fixity of the I.Q. has been dis- 

 proved. We know now that a stimulating environment in the home, in pre- 

 school, in elementary school, in high school, in college and in later life tend 

 to raise the I.Q. of an individual, and to maintain it at a higher level. We 

 know that in a depressed environment intelligence fails of a normal growth. 

 On the other hand, there are important differences between individuals in 

 the extent to which they respond to the stimulus of the same environment. 

 Individual differences do not disappear when the environment is equalized 

 at a high level. In a stimulating environment, able individuals show a ca- 

 pacity for response which takes them further than ever out of the class 

 of those of average ability. Among Newman's 19 pairs of identical twins 

 reared apart, there were 1 1 pairs in which the two members of each pair 

 had had similar amounts of education. In each such case the twins differed 

 in I.Q. only about as much as the same individual would vary when tested 

 at different times, the average of differences being 4.4 points. Among four 

 of the pairs there was considerable difference in schooling between the 

 members of each pair; their I.Q.'s differed on the average by 10 points. 

 Among the four remaining pairs, educational differences between the mem- 

 bers of each pair were large, and in these four cases the twins differed by 19 

 points, on the average. In every case the twin with the more education had 

 the higher I.Q. But at the same time where one twin was dull for his poor 

 environment, the other was dull for his good environment, and where one 

 twin responded well to his poor environment, his mate responded well to 

 his good environment. 



Twin Eleanore only got as far as the fifth grade, and attained an I.Q. of 

 only 66. Her sister Georgiana went through grade school, high school, 

 four years of music and three years of normal school. After all that educa- 

 tion, her I.Q. was only 78. It is hard to escape the conclusion that this pair 

 of identical twins were not endowed with the genetic factors necessary to 

 ordinary intelligence. 



Twin Gladys, with only three years' elementary schooling as the total 

 of her education, had the creditable I.Q. of 92. Her sister Helen, with a 

 college degree, had an I.Q. of 116. Evidently the genetic endowment of 

 these girls was sufficient for the development of average intelligence. 



