Heredity and the Environment & Development

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1. Influences Intelligence (positive or negatively depending on whether the environment is developmentally healthy or unhealthy. Does it support the child's cognitive development, for example? Are there books and educational toys in the environment to enhance learning? Or is the opposite true?)

E.g. today, almost all scientists agree that intelligence arises from the influence of both genetic and environmental factors. Careful study is required in order to attribute any influence to either environment or heredity. For example, one measure commonly used to assess a child's home environment is the number of books in the home. But having many books in the home may be related to the parents' IQ, because highly intelligent people tend to read more. The child's intelligence may be due to the parents' genes or to the number of books in the home. Further, parents may buy more books in response to their child's genetically influenced intelligence. Which of these possibilities is correct cannot be determined without thorough studies of all the factors involved.

E.g. some of the strongest evidence for genetic influences in intelligence comes from studies of identical twins adopted into different homes early in life and thus raised in different environments. Identical twins are genetically identical, so any differences in their IQ scores must be due entirely to environmental differences and any similarities must be due to genetics. Results from these studies indicate that the IQ scores of identical twins raised apart are highly similar—nearly as similar as those of identical twins raised together. For adoption studies to be valid, placement of twin pairs must be random. If brighter twin pairs are selectively placed in the homes of adoptive parents with higher intelligence, it becomes impossible to separate genetic and environmental influences. http://encarta.msn.com/encyclopedia_761570026_5/Intelligence.html#s24

E.g. the influence of heredity and familial environment may be distinguished by studying adoptees. For example, in one study, the authors present correlations in intelligence and educational level between genetically related pairs of adult adoptees who have been reared separately, and, conversely, between genetically unrelated pairs of adult adoptees who have been reared together. At the time of this study, ...