One
of the most important findings that has emerged from human behavioral
genetics involves the environment rather than heredity, providing the
best available evidence for the importance of environmental influences
on personality, psychopathology, and cognition. The research also converges
on the remarkable conclusion that these environmental influences make
two children in the same family as different from one another as are pairs
of children selected randomly from the population. The article has three
goals: (1) to describe quantitative genetic methods and research that
lead to the conclusion that nonshared environment is responsible for most
environmental variation relevant to psychological development, (2) to
discuss specific nonshared environmental influences that have been studied
to date, and (3) to consider relationships between non-shared environmental
influences and behavioral differences between children in the same family.
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