The adopted child's IQ: A critical review.

Abstract

This review summarizes all reliable published data about the nature and nurture of adopted children's IQs and draws conclusions about the relative importance of heredity and environment on children's mental development.Any study that compares the central tendency of adopted children's IQs with a group mean of 100 IQ points for a normal population cannot be taken seriously until several methodological criteria have been met: (a) representative sampling, (b) no differential loss of subjects over time, (c) accurate, age-corrected information on biological and adoptive parents, (d) careful attention to early separation and placement of children, and (e) elimination of practice effects and regression to the mean artifacts. Existing adoption studies that rely on group average comparisons are flawed by the biased sampling and other methodological problems that they all contain. On the other hand, some firm conclusions can be drawn from the resemblance between individual adopted children's IQ scores and their adoptive and biological parents' mental abilities. Analysis shows that the adoptive parents' home environment has only a modest effect on their adopted children's intellectual growth (r = .19 for 351 families), while the heredity and environment of the biological parents have a strong effect on their own children's intellectual growth (r = .58, n = 378 families). At present there is disagreement about the precise values of genetic and environmental effects on IQ, and several assumptions must be made before accurate statistics can be derived. But, the available data strongly suggest that under existing circumstances, heredity is much more important than environment in producing individual differences in IQ.After L. F. Richardson (1912-13) pro-adopted children and compared their scores posed the use of adopted x children to study with various groups to determine whether the nature and nurture of IQ, many investi-genetic or environmental factors exert more gators measured the mental development of influence on cognitive development. A mass of adoptive evidence on the nature-nurture Requests for reprints should be sent to Harry issue has accumulated within the last half Munsinger,

Family environment and the malleability of cognitive ability: A Swedish national home-reared and adopted-away cosibling control study

“…McNemar (7) demonstrated that the cognitive ability of the biological parents was almost certainly underestimated. Munsinger added the criticism that inadequate controls for attrition were applied, which seems to have favored the inclusion of the higher-ability children (8). Moreover, approximately a third of the effect appears to be attributable to the Flynn effect-i.e., increases in the mean level of cognitive ability between the maternal and offspring generations (9).…”

A Critical Analysis of IQ Studies of Adopted Children

“…Fundamental doubts about the methodology and empirical adequacy of IQ adoption studies have been expressed before [e.g., Lewontin, Rose, & Kamin, 1984;Munsinger, 1975]. But these do not cover more recent studies and the further interpretations of them, including the seemingly negligible eff ects of parents, or betweenfamily environments [Collins, Maccoby, Steinberg, Hetherington, & Bornstein, 2000; see also Sacerdote, 2004].…”

personnes qui ont été adoptées :

“…Ces études ont exploré différentes caractéristiques des personnes qui ont été adoptées dont, notamment, l'attachement (v.g., Morison & Ellwood, 2000 ;O'Connor, Rutter, & Romanian Adoptees Study Team, 2000), la santé mentale (v.g., Cederblad, Hôôk, Irhammar, & Mercke, 1999), l'estime de soi (v.g., Steward & Lynn, 1990), l'identité, (v.g., Sorosky, Baran, & Pannor, 1975, le processus de recherche et de retrouvailles avec la famille biologique (v.g., Campbell, Silverman, & Parti, 1991), la relation avec les parents adoptifs (v.g., Rosnati & Marta, 1997), les troubles de comportements (v.g., Peters, Atkins, & McKay, 1999), l'ajustement scolaire (Maughan, Collishaw, & Pickles, 1998 ;Sharma, McGue, & Benson, 1998 ;Stams, Juffer, Rispens, & Hoksbergen, 2000) et les habiletés intellectuelles (v.g., Capron & Duyme, 1969 ;Musinger, 1975a ;Wadsworth, DeFries, & Plomin, 1993 ;Wierzbicki, 1993).…”