From your own linkAn especially surprising finding emerging from the body of behavior genetics work has been that the effects of nonshared environment appear to be much greater than those of shared environment see Plomin Daniels 1987 and Plomin et al 1994 . Recent estimates of nonshared environmental effects are much reduced when measurement error is taken into account Rutter et al 1999 . And a number of studies of social behavior or pathology have found substantial sharedenvironment effects . Nevertheless , shared environmental effects consistently emerge as small , and indeed are often reported as being close to zero Plomin Bergeman 1991 . Adopted children do not appear to resemble their adoptive siblings or parents any more closely than they resemble children growing up in different households . Also , in many respects fraternal twinsor ordinary siblings , for that matterdo not greatly resemble each other or their parents . Critics have urged that it is not valid to estimate environmental effects , either shared or unshared , without measuring them Goodman 1991 , Hoffman 1991 , Rose 1995 , Stoolmiller 1999 , Patterson 1975 . Recent work has involved designs in which both genetic and environmental factors have been directly assessed . For example , a group of leading behavior geneticists and leading students of parentchild interaction collaborated in a study comparing children of different degrees of genetic relatedness twins , full siblings , half siblings , step siblings , in which parental childrearing inputs were assessed through observations of parentchild interactions , as well as through parent and child reports Reiss 1997 , Reiss et al 1999 , Hetherington et al 1999 . Relying on the additive assumption , these investigators have partitioned the variance in child adjustment outcomes into the three components G , Es , and Eus , reporting substantial contributions from genetics . Effects of shared environment are variable , making clear contributions to some outcomes but not others in general , though , they are considerably smaller than the substantial contributions from unshared environment . Studies that don ' t control for genetics shouldn ' t be trusted . And it ' s not about isolated factors . It ' s about that of genes , shared , and unshared environment , we can quantify the importance of each . Genes usually come out on top and shared environment mostly doesn ' t matter .