Does intelligence have a stronger genetic or environmental basis?
- Understanding the empirical findings of research pointing to a genetic or environmental basis of intelligence
- Twin and Adoption studies and predictions to be made regarding the environmental contributions in acquired intelligence
- Empirical research within the behavioral genetics
- Twin designs: The most reliable estimate of the genetic component of intelligence
- Large-scale studies of adoptees: Texas, Minnesota and Colorado
- The conclusion that shared environment has a greater influence on environmental variation
In light of the pioneering nature of behavioral genetics and in terms of explanatory power and predictive ability, highlighting constructive directions for future research, the aim of the current essay is to examine a wealth of evidence within the field of behavioral genetics to provide a well-versed argument for both environmental and genetic influences on the development of intellectual abilities. In line with behavioral genetic theory, it is possible to systematically test the degree to which variability is the result of genetic or non-genetic individual differences (Loehlin, Horn & Willerman, 1989., Plomin & Daniels, 1987). By examining the relevant research therefore, it should be possible to determine the extent to which environmental or genetic influences provide the most adequate explanation for a basis of intelligence. In order to understand the empirical findings of research pointing to a genetic or environmental basis of intelligence it is first necessary to briefly identify the basic aims and methods used in the study of behavioral genetics.
[...] Whether this portion of variance has a stronger shared or non-shared environmental influence is slightly less abated however. Typically findings of adoption research yield an estimate of 30 per cent of the variance attributable to the environment shared between parents, offspring and siblings (Loehlin et al Scarr & Weinberg c.f. Plomin & Daniels Scarr Wilson, 1983). In understanding the literature, it was noted that studies of twins reared together provided the most direct estimate of non-shared environment. Findings of such studies (Bouchard et al., 1990a Thompson c.f. [...]
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