Adoption Studies

Adoption studies may be the most powerful behavioral genetic method available. In an adoption study , one can examine the correlations between adopted children and their adoptive parents, with whom they share no genes. If one finds a positive corre lation between adopted children and their adoptive parents, then this provides strong evidence for environmental influences on the personality trait in question

Similarly, we can examine the correlations between adopted children and their genetic parents, who had no influence on the children s environments. If we find a zer correlation between adopted children and their genetic parents, again this is strong evidence for a lack of heritable influence on the personality trait in question. Conversel , if we find a positive correlation between parents and their adopted-away children, wit whom they have had no contact, then this provides evidence for heritability .

Adoption studies are especially powerful because they allow us to get around the equal environments assumption, which must be made in twin studies. In twin studies, because parents provide both genes and environments to their children, and may provide more similar environments for identical than for fraternal twins, there is a potential compromise of the equal environments assumption. In adoption studies, however, genetic parents provide none of the environmental influences on their chil dren, thus unconfounding genetic and environmental causes.

Adoption studies, however, are not without potential problems of their own. Perhaps the most important potential problem is the assumption of representativeness. Adoption studies assume that adopted children, their birth parents, and their adoptive parents are representative of the general population. For example, these studies assume that couples who adopt children are not any dif ferent from couples who do not adopt children. Fortunately, the assumption of representativeness can be tested directly. Several studies have confirmed that the assumption of representativeness holds for cog nitive abilities, personality , education level, and even socioeconomic status (Plomin & DeFries, 1985; Plomin, DeFries, & Fulker , 1988).

Another potential problem with adoption studies is selective placement. If adopted children are placed with adoptive parents who are similar to their birth parents, then this may inflate the correlations between the adopted children and thei adoptive parents. In this case, the resulting inflated correlations artificially inflate es mates of environmental influence, since the correlation appears to be due to the envi ronment provided by the adoptive parent. Fortunately , there does not seem to be selective placement, so this potential problem is not a problem in actual studies (Plomin et al., 1990).

Without a doubt, one of the most powerful behavioral genetic designs is one that combines the strengths of twin and adoption studies at the same time, by studying twins reared apart. In fact, the correlation between identical twins reared apart can be interpreted directly as an index of heritability . If identical twins reared apart show a correlation of + .65 for a particular personality characteristic, then that means that 65 percent of the individual dif ferences are heritable. Unfortunately , identical twins reared apart are exceedingly rare. Only more recently have painstaking ef forts been undertaken to find such twins and study them (Segal, 1999). The effort has been well worth it, as such studies have yielded a bounty of fascinating results, to which we now turn. A summary of the behavioral genetic methods, along with their advantages and limitations, is shown in T able 6.1.

Table 6.1 Summary of Behavioral Genetic Methods

Method

Advantages

Limitations

Selective breeding studies

Can infer heritability if selective breeding works

Are unethical to conduct on humans

Family studies

Provide heritability estimates

Violate equal environments assumption

Twin studies

Provide both heritability and environmentality estimates

Sometimes violate equal environments assumption; may violate assumption of representativeness

Adoption studies

Provide both heritability and environmentality estimates; get around the problem of equal environments assumption

Adopted kids might not be representative of population; problem of selective placement

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Responses

  • Cupido
    How to adopt the human personality?
    3 years ago
  • tewolde
    What are the adoption studies in psychology?
    1 year ago
  • elizabeth
    What are adoption studiesfor personality?
    1 year ago
  • nasih
    Is adoption positive study?
    8 months ago
  • ilse
    How can selective placement compromise a study in psychology?
    5 months ago
  • piera giordano
    Which of the following are results from twin and adoption personality studies?
    4 months ago

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