In the coming years we can look forward to research that clarifies specific mechanisms that
account for the interplay between genetic and environmental influences on psychological
development. Certain misconceptions, arising from research traditions initiated by Francis
Galton on the one hand and G. Stanley Hall on the other, may now be set aside in the light of
new evidence. Three important findings promise a new synthesis. First, while each of us is born
with about 100,000 genes that, under ordinary circumstances, do not change, the expression of
these genes on behavior is dynamic. Some genetic influences are expressed early in development,
but others are manifest many years later. Second, genetic factors often account not only for some
of the individual differences in the measures of adjustments we typically use to monitor
development but also for individual differences in environmental experiences that covary with
those measures of adjustment. Indeed, genetic factors have been found to account for a surprising
amount of covariance between measures of the social environment and of adjustment in young
children, adolescents, and adults. Third, the expression of genetic influences are very malleable
and responsive to the social environment. These new findings are revealing specific mechanisms
for the interplay of genetic and social environmental factors in four domains. First, the social
environment may play both a necessary and specific role in the expression of particular genetic
influences on a range of behaviors from depression to social responsibility. Second, an
understanding of the interplay between the social environment and genetics may lead to a clearer
definition of the phenotypic manifestations of particular genetic influences. Third, we
will—as a result of these studies—have a clearer fix on the timing of important
events and their sequence in development. Fourth, this new genre of work promises to illumine
more completely mechanisms by which the social environment influences development
independent of genetic influence.