Effects of families on intellectual development.

Comments that we know less than we think about the direct influence of environment on the causes of intellectual differences among individuals. It is valuable to examine the results of adoption studies, since some separation of hereditary and environmental influences can be achieved. Results suggest that factors such as parental education and intelligence have only a small impact on the intelligence of their children. A very large fraction of the environmental causes of individual differences remains unexplained. It is hypothesized that many of these influences are fortuitous and biological in nature. These factors can include unrecognized head injuries, viruses, and subtle inborn errors of metabolism; the latter leading to mismatches between the individual's genes and the specific environments to which he or she is exposed. (24 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)