Adoption study

Adoption studies typically compare pairs of persons, e.g., adopted child and adoptive mother or adopted child and biological mother, to assess genetic and environmental influences on behavior.[1] These studies are one of the classic research methods of behavioral genetics. The method is used alongside twin studies to identify the roles of genetics and environmental variables that impact intelligence, and behavioral disorders.[2]

This Article includes information about study designs and methods. It will also include examples of real-life scenarios including mental disorders, cognitive ability, crime, and alcoholism.

Study Designs and Methods

There are two standard ways in which adoption studies are carried out; the adoptee's study method and the adoptee's family method.The adoptee's study method compares adoptee's similarity to their biological and adoptive parents.[3] Similarity with the biological parent is expected to be due to genetics, while similarity with the adoptive parent is due to home-environment, which is referred as the shared environmental effect.The adoptee's family method compares non-biological siblings who are reared in the same household.[4] Similarity to non-biological siblings raised in the same household is attributed to shared environmental effect, as the siblings are genetically unrelated but share the home environment.

Variation that cannot be accounted for by either genetics or home-environment is typically described as a non-shared environment.

Examples

Mental disorders

The first adoption study on schizophrenia published in 1966 by Leonard Heston demonstrated that the biological children of parents with schizophrenia were just as likely to develop schizophrenia whether they were reared by their parents or adopted[5] and was essential in establishing schizophrenia as being largely genetic instead of being a result of child rearing methods.[6][7] Analogous studies that followed have shown that mental disorders such as alcoholism, antisocial behavior and depression have a large genetic component that can interact with environmental risk factors such as family conflict, poor coherence, and deviant communication.[4]

Cognitive ability

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 and disappeared. The correlation with the biological parent seemed to explain most of the variation. In 2015 an adoption study that compared Swedish male-male full-sibships in which at least one member was reared by one or more biological parents and the other by adoptive parents was published. Parental education level was rated on a 5-point scale and each additional unit of rearing parental education was associated with 1.71 points higher IQ. The results were replicated with 2 341 male-male half-sibships, controlling for clustering within families, each additional unit of rearing parental education was associated with 1.94 IQ units.[11]

Crime

One of the most influential and widely cited adoption study on criminality was conducted by Sarnoff A. Mednick and Karl O. Christiansen in Denmark. They argued that relevant data demonstrated that criminality has a significant genetic component that interacts with environmental risk factors.[12] Adoption studies that followed have had similar results.[4]

Alcoholism

In the mid-1970s, adoption studies were conducted to investigate the effects on children of having a biological parent with alcoholism. The study found that sons whose biological father has alcoholism were four times more likely to develop alcoholism within their lifetime, but were not more likely to have other mental disorders. The study, was unable to conclude what the impact was on daughters.[13][14] A more recent study was published in 2009 which compared the parental alcoholism of children in non-adoptive and adoptive families. This study found that the likelihood of children developing alcoholism later in life was associated more with genetic rather than environmental factors.[15]

References
  1. Palmer, Rohan; Hahn, Martin (2011), Kreutzer, Jeffrey S.; DeLuca, John; Caplan, Bruce (eds.), "Adoption Studies", Encyclopedia of Clinical Neuropsychology, New York, NY: Springer, pp. 41–42, doi:10.1007/978-0-387-79948-3_1854, ISBN 978-0-387-79948-3, retrieved 2023-10-19
  2. Blackman, Michael (September 1995). "Chemical patent footballs". World Patent Information. 17 (3): 195–200. doi:10.1016/0172-2190(95)00025-u. ISSN 0172-2190.
  3. Cadoret, Remi J. (1995). "Adoption Studies". Alcohol Health and Research World. 19 (3): 195–200. ISSN 0090-838X. PMC 6875765. PMID 31799970.
  4. Tsuang, MT; Bar, JL; Stone, WS; Faraone, SV (2004). "Gene-environment interactions in mental disorders". World Psychiatry. 3 (2): 73–83. PMC 1414673. PMID 16633461.
  5. Heston, Leonard L. (August 1966). "Psychiatric Disorders in Foster Home Reared Children of Schizophrenic Mothers - The British Journal of Psychiatry". The British Journal of Psychiatry. 112 (489): 819–825. doi:10.1192/bjp.112.489.819. PMID 5966555. S2CID 37953097.
  6. Joseph, Jay (2004). The Gene Illusion. Algora. ISBN 9780875863450 – via google.fi.
  7. Disorders, Institute of Medicine (US) Committee on Prevention of Mental; Mrazek, Patricia J.; Haggerty, Robert J. (1994). Risk and Protective Factors for the Onset of Mental Disorders. National Academies Press (US).
  8. Loehlin, JC; Horn, JM; Willerman, L (1989). "Modeling IQ Change: Evidence from the Texas Adoption Project". Child Development. 60 (4): 993–1004. doi:10.2307/1131039. JSTOR 1131039. PMID 2758892.
  9. Rhea, SA; Bricker, JB; Wadsworth, SJ; Corley, RP (2013). "The Colorado Adoption Project". Twin Res Hum Genet. 16 (1): 358–65. doi:10.1017/thg.2012.109. PMC 3817005. PMID 23158098.
  10. Scarr S and Weinberg RA (1983). "The Minnesota Adoption Studies: genetic differences and malleability". Child Dev. 54 (2): 260–7. doi:10.2307/1129689. JSTOR 1129689. PMID 6872626.
  11. Kenneth S. Kendler (2015). "Family environment and the malleability of cognitive ability: A Swedish national home-reared and adopted-away cosibling control study". PNAS. 112 (15): 4612–7. Bibcode:2015PNAS..112.4612K. doi:10.1073/pnas.1417106112. PMC 4403216. PMID 25831538.
  12. "NCJRS Abstract - National Criminal Justice Reference Service". ncjrs.gov.
  13. Goodwin, D. W. (1977), Thurman, Ronald G.; Williamson, John R.; Drott, Henry R.; Chance, Britton (eds.), "Adoption Studies of Alcoholism", Alcohol and Aldehyde Metabolizing Systems, Academic Press, pp. 643–648, doi:10.1016/b978-0-12-691403-0.50067-7, ISBN 978-0-12-691403-0, retrieved 2022-07-16
  14. Goodwin, D. W. (1976). "Adoption studies of alcoholism". Journal of Operational Psychiatry. 7 (1): 54–63.
  15. King, Serena M.; Keyes, Margaret; Malone, Stephen M.; Elkins, Irene; Legrand, Lisa N.; Iacono, William G.; McGue, Matt (April 2009). "Parental alcohol dependence and the transmission of adolescent behavioral disinhibition: a study of adoptive and non-adoptive families". Addiction. 104 (4): 578–586. doi:10.1111/j.1360-0443.2008.02469.x. PMC 2751628. PMID 19215604.

Sources
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