Nature-Nurture and Intelligence.

Abstract

This is, in our opinion, the best and most carefully controlled of the studies of foster children. It was undertaken in an attempt to resolve the different results obtained by two previous studies, the earlier Freeman-Chicago Study and the Burks-Stanford Study. Give special attention to the criteria of selection for the two groups of children and homes. You should also attend to the correlational indices and mean differences in intelligence shown in the various comparisons. Less than half of the monograph has been reprinted here; the interested reader will find further valuable details in the complete account. Nature-Nurture and Intelligence* ALICE M. LEAHY THE PROBLEMVariation in human intelligence is universally recognized. But experimentation to discover the causes which affect this variation has moved slowly. The reasons are obvious. First, conditions which permit the control of either heredity or environment are difficult to secure, and secondly, our tools for measurement are limited and crude. Although identical twins provide an absolute control of heredity, their separate location in diverse environments is rare. Experimentation involving the control of environment, on the other hand, is not entirely possible. Measures are available for only certain of its features. For its dynamic attributes we have no measures. Hence, what may appear to be similar environments are only approximately identical. However, the individual mental examination has been demonstrated to be fairly reliable of what may be called test intelligence.The present investigation approaches the problem by a comparison of two groups of children living in approximately identical environments. In one group, the children are unrelated by blood or marriage to the persons shaping the environment. They are adopted children. In the other group, the children are the offspring of the persons who have shaped the environment. Both heredity and environment are operative in the latter group, while in the former, only environment.Resemblance as expressed by means of the correlation between attributes in the home and test intelligence of child will constitute one type of analysis.

Genetic and environmental influences on human psychological differences

“…In fact, and as shown in Figure 3, a major contributor to the heterogeneity in the adoptive sibling correlation is the age of the sample. The childhood data are from Burks (1928), Freeman et al (1928), Leahy (1935), Skodak (1950), Scarr and Weinberg (1977), and Horn et al (1979). The adult data are from Scarr and Weinberg (1978), Teasdale and Owen (1984), Scarr et al (1993), Loehlin et al (1997), andSegal (2000).…”

Genetic Research in Psychiatry and Psychology

“…The goal of the earliest adoption studies was to assess the role of genetic and environmental influences on IQ (e.g., Burks, 1928;Leahy, 1935;Skodak & Skeels, 1949). These were followed a few decades later by a new group of IQ studies, which included the Minnesota Adoption Study (MAS; Scarr & Weinberg, 1978), the Texas Adoption Project (TAP; Horn, Loehlin, & Willerman, 1979;Loehlin, Horn, & Willerman, 1989), and the Colorado Adoption Project (CAP; Plomin & DeFries, 1985;Plomin, Fulker, Corley, & DeFries, 1997).…”

personnes qui ont été adoptées :

“…Musinger (1975b) a fait une revue de la littérature portant sur le quotient intellectuel d'enfants qui ont été adoptés. Il présente un tableau qui compile les données de quatre études (Burks, 1928 ;Leahy, 1935 ;Musinger, 1975b ;Skodak & Skeels, 1945, 1949 Selon la littérature, il appert ainsi que l'origine ethnique peut avoir un effet sur les habiletés intellectuelles des personnes qui ont été adoptées. De plus, une étude démontre que l'origine ethnique des familles d'adoption peut également avoir un effet sur les habiletés intellectuelles des enfants qui ont été adoptés.…”