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The most cited adoption projects that sought to estimate the heritability of IQ were those of Texas, [8] Colorado [9] and Minnesota [10] that were started in the 1970s. These studies showed that while adoptive parents IQ does seem to have a correlation with adoptees IQ in early life, when the adoptees reach adolescence the correlation has faded ...
Thomas J. Bouchard Jr. (born October 3, 1937) is an American psychologist known for his behavioral genetics studies of twins raised apart. He is professor emeritus of psychology and director of the Minnesota Center for Twin and Adoption Research at the University of Minnesota.
Studies of human heritability often utilize adoption study designs, often with identical twins who have been separated early in life and raised in different environments. Such individuals have identical genotypes and can be used to separate the effects of genotype and environment.
The power of twin designs arises from the fact that twins may be either identical (monozygotic (MZ), i.e. developing from a single fertilized egg and therefore sharing all of their polymorphic alleles) or fraternal (dizygotic (DZ), i.e. developing from two fertilized eggs and therefore sharing on average 50% of their alleles, the same level of genetic similarity found in non-twin siblings).
This led to major advances in model organism research (e.g., knockout mice) and in human studies (e.g., genome-wide association studies), leading to new scientific discoveries. Findings from behavioural genetic research have broadly impacted modern understanding of the role of genetic and environmental influences on behaviour.
In adoption studies, selective placement refers to the practice by which adoption agencies tend to deliberately match certain characteristics of an adopted child's adopted parents with those of his or her biological parents. When this occurs, it results in a correlation between environments between biological relatives raised in different homes.
Hereditarianism is the research program according to which heredity plays a central role in determining human nature and character traits, such as intelligence and personality. Hereditarians believe in the power of genetic influences to explain human behavior and solve human social-political problems.
Twin and family studies have long been used to estimate variance explained by particular categories of genetic and environmental causes. Across a wide variety of human traits studied, there is typically minimal shared-environment influence, considerable non-shared environment influence, and a large genetic component (mostly additive), which is on average ~50% and sometimes much higher for some ...