Etiology of verbal and performance delays were investigated in a large population sample of twins at 2 and 3 years (N=2,449 pair). Longitudinal genetic analyses indicated substantial heritability of verbal delay from 2 to 3 years, especially in combination with performance delay. Results suggest a strong genetic contribution to verbal delay…

This book aims: (1) to describe and evaluate psychological research on poor children's intellect; to this end, the following questions are dealt with: What is the nature of poor children's mental abilities? How do these abilities develop? (2) to analyze the psychological assumptions underlying several attempts to reform education; and, (3) to…

Reviews the current theories concerning individual differences in cognitive functioning. While some argue that heredity places a genetic cap on intellectual development, others emphasize the dynamic interrelationship between cultural and environmental factors. Concludes that intelligence is more complex than the heredity advocates allow. (MJP)

Psychologists and a few sociologists have provided the academic respectability for the political rationale that the American body politic's civil rights indigestion needs a resurrected, separate but equal diet. Today, it is intellectually respectable to question the genetic equality of whites and blacks, to assert the cognitive incapacities of…

This final report reviews the second phase of a life-span study of boys with fragile X syndrome (FSX), the most common known inherited cause of mental retardation. Males with the syndrome are more severely affected than females and in males, delays are usually evident in all the developmental domains, although cognitive and communication skills…