Environmental influences that are individually specific (i.e., the effects are not shared by family members). The distinction between shared environment and non-shared environment is not always clear. For example, does a peer group constitute a shared environment, or do peer groups differ influences between members of the same family such that an individual selects a peer group that suits his or her age-related personality and aspirations? This distinction is particularly a problem for the claim made by Judith Rich Harris in her controversial book The nurture assumption: why children turn out the way they do (1998) that peer group pressures exert more effects on adult psychological outcomes than do parents or the family, given the reliance she places on behavior genetics in her book in order to be able to make this claim. Not surprisingly, Harris and her standpoint has been subjected to criticism, which to her includes on her website.
See Behavior genetics, Etiology, Hereditary, Heritability, Nature-nurture debate, Peer group, Shared environment