Adoption study

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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]

Contents

Adoption studies differ from twin studies in that adoption studies do not necessarily need to use twins; instead, they compare the traits of children to their parents, whether those are the adoptive parents or biological parents. [1]

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] The study in Minnesota was conducted by Bouchard. It had an emphasis on identical twins that were separated and raised by different families. [12]

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. [13] Adoption studies that followed have had similar results. [4] "The Stockholm adoption study (2000 adoptees) found that criminality alone was not transmitted from biological parents to adoptees, but did find elevated rates of criminality in adopted-away offspring of biological parents with alcohol use disorders (AUD) alone, or with both AUD and criminality (Bohman, 1978)." [14]

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. [15] [16] 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. [17]

Obesity

Adoption studies have been used to study childhood obesity. This study showed a strong correlation for the environmental argument. Children were strongly influenced by adopted parents weight till mid childhood. During adolescence this dissipated. This study also showed that the biological parents and children had an even stronger correlation when it came to weight and BMI. This put more emphasis on genes than environment. [18]

History

In the early to mid-nineteen hundreds, we can find some evidence of adoption studies. These studies were thought to be very important as they wanted to match children with parents in every way possible. They thought they should be similar in looks, class, and mental capacities. They had methods of testing children to find out how smart they were. Mental tests were popularized by Goddard who used a version of the Binet scale. The Gesell Scale was made and became the most widely used by adoption agencies in the 1940s. This is a way of testing a baby's intelligence. This is determined through normal growth, development, and mental milestones. This raised some social and moral issues some children were deemed unfit for adoption because of their low mental test scores. The outcome of these selective adoption studies found that ultimately had no effect on the happiness or success of the children. It also had no effect on the satisfaction of the parents. [19]

Related Research Articles

<span class="mw-page-title-main">Adoption</span> Parenting a child in place of the original parents

Adoption is a process whereby a person assumes the parenting of another, usually a child, from that person's biological or legal parent or parents. Legal adoptions permanently transfer all rights and responsibilities, along with filiation, from the biological parents to the adoptive parents.

Nature versus nurture is a long-standing debate in biology and society about the relative influence on human beings of their genetic inheritance (nature) and the environmental conditions of their development (nurture). The alliterative expression "nature and nurture" in English has been in use since at least the Elizabethan period and goes back to medieval French. The complementary combination of the two concepts is an ancient concept. Nature is what people think of as pre-wiring and is influenced by genetic inheritance and other biological factors. Nurture is generally taken as the influence of external factors after conception e.g. the product of exposure, experience and learning on an individual.

Twin studies are studies conducted on identical or fraternal twins. They aim to reveal the importance of environmental and genetic influences for traits, phenotypes, and disorders. Twin research is considered a key tool in behavioral genetics and in related fields, from biology to psychology. Twin studies are part of the broader methodology used in behavior genetics, which uses all data that are genetically informative – siblings studies, adoption studies, pedigree, etc. These studies have been used to track traits ranging from personal behavior to the presentation of severe mental illnesses such as schizophrenia.

<span class="mw-page-title-main">Human behaviour genetics</span> Field that examines the role of genetic and environmental influences on human behaviour

Human behaviour genetics is an interdisciplinary subfield of behaviour genetics that studies the role of genetic and environmental influences on human behaviour. Classically, human behavioural geneticists have studied the inheritance of behavioural traits. The field was originally focused on determining the importance of genetic influences on human behaviour. It has evolved to address more complex questions such as: how important are genetic and/or environmental influences on various human behavioural traits; to what extent do the same genetic and/or environmental influences impact the overlap between human behavioural traits; how do genetic and/or environmental influences on behaviour change across development; and what environmental factors moderate the importance of genetic effects on human behaviour. The field is interdisciplinary, and draws from genetics, psychology, and statistics. Most recently, the field has moved into the area of statistical genetics, with many behavioural geneticists also involved in efforts to identify the specific genes involved in human behaviour, and to understand how the effects associated with these genes changes across time, and in conjunction with the environment.

<span class="mw-page-title-main">Gene–environment interaction</span> Response to the same environmental variation differently by different genotypes

Gene–environment interaction is when two different genotypes respond to environmental variation in different ways. A norm of reaction is a graph that shows the relationship between genes and environmental factors when phenotypic differences are continuous. They can help illustrate GxE interactions. When the norm of reaction is not parallel, as shown in the figure below, there is a gene by environment interaction. This indicates that each genotype responds to environmental variation in a different way. Environmental variation can be physical, chemical, biological, behavior patterns or life events.

The Minnesota Transracial Adoption Study examined the IQ test scores of 130 black or interracial children adopted by advantaged white families. The aim of the study was to determine the contribution of environmental and genetic factors to the poor performance of black children on IQ tests as compared to white children. The initial study was published in 1976 by Sandra Scarr and Richard A. Weinberg. A follow-up study was published in 1992 by Richard Weinberg, Sandra Scarr and Irwin D. Waldman. Another related study investigating social adjustment in a subsample of the adopted black children was published in 1996. The 1992 follow-up study found that "social environment maintains a dominant role in determining the average IQ level of black and interracial children and that both social and genetic variables contribute to individual variations among them."

The Minnesota Center for Twin and Family Research is a series of behavioral genetic longitudinal studies of families with twin or adoptive offspring conducted by researchers at the University of Minnesota. It seeks to identify and characterize the genetic and environmental influences on the development of psychological traits.

Research on the heritability of IQ inquires into the degree of variation in IQ within a population that is due to genetic variation between individuals in that population. There has been significant controversy in the academic community about the heritability of IQ since research on the issue began in the late nineteenth century. Intelligence in the normal range is a polygenic trait, meaning that it is influenced by more than one gene, and in the case of intelligence at least 500 genes. Further, explaining the similarity in IQ of closely related persons requires careful study because environmental factors may be correlated with genetic factors.

<i>The Gene Illusion</i> Book by Jay Joseph

The Gene Illusion is a 2003 book by clinical psychologist Jay Joseph, in which the author challenges the evidence underlying genetic theories in psychiatry and psychology. Focusing primarily on twin and adoption studies, he attempts to debunk the methodologies used to establish genetic contributions to schizophrenia, criminal behaviour, and IQ. In the nature and nurture debate on the causes of mental disorders, Joseph's criticisms of genetic research in psychiatry have found their place among those who argue that the environment is overwhelmingly the cause of these disorders, particularly with psychiatry critic Jonathan Leo, and with Oliver James. It was also reviewed favorably in Choice and the British Journal of Learning Disabilities. Some of the conclusions of The Gene Illusion have been criticized in reviews of the book.

Psychiatric genetics is a subfield of behavioral neurogenetics and behavioral genetics which studies the role of genetics in the development of mental disorders. The basic principle behind psychiatric genetics is that genetic polymorphisms are part of the causation of psychiatric disorders.

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<span class="mw-page-title-main">Irving Gottesman</span> Psychiatric geneticist

Irving Isadore Gottesman was an American professor of psychology who devoted most of his career to the study of the genetics of schizophrenia. He wrote 17 books and more than 290 other publications, mostly on schizophrenia and behavioral genetics, and created the first academic program on behavioral genetics in the United States. He won awards such as the Hofheimer Prize for Research, the highest award from the American Psychiatric Association for psychiatric research. Lastly, Gottesman was a professor in the psychology department at the University of Minnesota, where he received his Ph.D.

Sarnoff Andrei Mednick, was a psychologist who pioneered the prospective high-risk, longitudinal study to investigate the etiology (causes) of psychopathology, or mental disorders. His emphasis was on schizophrenia. He made significant contributions to the study of creativity, psychopathy, alcoholism and suicide in schizophrenia. He was a Professor Emeritus at The University of Southern California, where he had been a tenured professor since the early '70s and remained highly active in his eighties. Mednick was the first scientist to revisit the genetic basis of mental disorders, following the era of eugenics. He was the recipient of the Joseph Zubin Award in 1996, with more than 300 peer-reviewed publications on the topic.

Behavioural genetics, also referred to as behaviour genetics, is a field of scientific research that uses genetic methods to investigate the nature and origins of individual differences in behaviour. While the name "behavioural genetics" connotes a focus on genetic influences, the field broadly investigates the extent to which genetic and environmental factors influence individual differences, and the development of research designs that can remove the confounding of genes and environment. Behavioural genetics was founded as a scientific discipline by Francis Galton in the late 19th century, only to be discredited through association with eugenics movements before and during World War II. In the latter half of the 20th century, the field saw renewed prominence with research on inheritance of behaviour and mental illness in humans, as well as research on genetically informative model organisms through selective breeding and crosses. In the late 20th and early 21st centuries, technological advances in molecular genetics made it possible to measure and modify the genome directly. This led to major advances in model organism research and in human studies, leading to new scientific discoveries.

The epigenetics of schizophrenia is the study of how inherited epigenetic changes are regulated and modified by the environment and external factors and how these changes influence the onset and development of, and vulnerability to, schizophrenia. Epigenetics concerns the heritability of those changes, too. Schizophrenia is a debilitating and often misunderstood disorder that affects up to 1% of the world's population. Although schizophrenia is a heavily studied disorder, it has remained largely impervious to scientific understanding; epigenetics offers a new avenue for research, understanding, and treatment.

Research into relative outcomes of parenting by biological and adoptive parents has produced a variety of results. When socioeconomic differences between two-biological-parent and two-adoptive-parent households are controlled for, the two types of families tend to invest a similar amount of resources. A 20-year longitudinal study of 245 adoptees placed in the first few months of life that compared the children's cognitive abilities with those of their birth and adoptive parents found that before age 5, the adoptees' cognitive skills correlated more with those in their adoptive families, but as the adoptees matured, their cognitive skills, including verbal ability, became more like those of their biological parents; thus, the study concluded that "environmental transmission from parent to offspring has little effect on later cognitive ability." Adopted siblings have, on average, an IQ score 4.4 points higher than the siblings who are reared by their biological parents and 3.18 point increase for half-siblings reared by their biological parents.

Post-adoption depression is shown though symptoms of depression in the adoptive mother or father, generally seen from one month after adoption, and is experienced by anywhere from 10% to 32% of adoptive parents. The symptoms of post-adoption depression are common to symptoms of depression, and include changes in sleeping pattern and appetite, feelings of hopelessness, fatigue, problems with concentration and restlessness, as well as suicidal thoughts. These symptoms are also similar to those of postpartum depression, which is a related syndrome. Postpartum depression, however, involves hormonal changes in pregnant woman, which are not present in women suffering from post-adoption depression. Despite this difference, there are still significant changes that new parents go through, even when the child is not biologically their own. These changes can have significant impacts on mental health. Post-adoption depression can also negatively impact the child.

In the context of the nature-nurture debate, interactionism is the view that all human behavioral traits develop from the interaction of both "nature" and "nurture", that is, from both genetic and environmental factors. This view further holds that genetic and environmental influences on organismal development are so closely interdependent that they are inseparable from one another. Historically, it has often been confused with the statistical concept of gene-environment interaction. Historically, interactionism has presented a limited view of the manner in which behavioral traits develop, and has simply demonstrated that "nature" and "nurture" are both necessary. Among the first biologists to propose an interactionist theory of development was Daniel Lehrman. Since then, numerous interactionist perspectives have been proposed, and the contradictions between many of these perspectives has led to much controversy in evolutionary psychology and behavioral genetics. Proponents of various forms of interactionist perspectives include Philip Kitcher, who refers to his view as "causal democracy", and Susan Oyama, who describes her perspective as "constructive interactionism". Critics of interactionism include major figures in behavioral genetics such as Arthur Jensen, Robert Plomin, and philosopher Neven Sesardic.

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. It has the potential to bias the conclusions of such studies, because twins who were reared in separate environments may in fact have been reared in much more similar environments than assumed. This can result in an inflated estimate of heritability. There is evidence that selective placement was a major confound in many early studies of twins reared apart. Some adoption studies report little or no evidence of selective placement. For example, a 1979 study by Ho et al. reported a generally low level of selective placement in adopted children for either physical or behavioral traits. The authors concluded that to the extent that selective placement occurred for such traits, "our data suggest that it is based largely on characteristics of the birth father," rather than those of the adoptee. Carey (2003) concluded that selective placement was "moderate" for physical characteristics and typically "small or nonexistent" for behavioral characteristics.

Gene-environment interplay describes how genes and environments work together to produce a phenotype, or observable trait. Many human traits are influenced by gene-environment interplay. It is a key component in understanding how genes and the environment come together to impact human development. Examples of gene-environment interplay include gene-environment interaction and gene-environment correlation. Another type of gene-environment interplay is epigenetics, which is the study of how environmental factors can affect gene expression without altering DNA sequences.

References

  1. 1 2 Palmer, Rohan; Hahn, Martin (2011), "Adoption Studies", in Kreutzer, Jeffrey S.; DeLuca, John; Caplan, Bruce (eds.), 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
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  3. ↑ Cadoret, Remi J. (1995). "Adoption Studies". Alcohol Health and Research World. 19 (3): 195–200. ISSN   0090-838X. PMC   6875765 . PMID   31799970.
  4. 1 2 3 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. ↑ Sahu, Monalisha; Prasuna, JosyulaG (2016). "Twin studies: A unique epidemiological tool". Indian Journal of Community Medicine. 41 (3): 177–182. doi: 10.4103/0970-0218.183593 . ISSN   0970-0218. PMC   4919929 . PMID   27385869.
  13. ↑ "NCJRS Abstract - National Criminal Justice Reference Service". ncjrs.gov.
  14. ↑ Kendler, K. S.; Larsson Lönn, S.; Morris, N. A.; Sundquist, J.; Långström, N.; Sundquist, K. (July 2014). "A Swedish national adoption study of criminality". Psychological Medicine. 44 (9): 1913–1925. doi:10.1017/S0033291713002638. ISSN   0033-2917. PMC   4009388 . PMID   24180693.
  15. ↑ 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
  16. ↑ Goodwin, D. W. (1976). "Adoption studies of alcoholism". Journal of Operational Psychiatry. 7 (1): 54–63.
  17. ↑ 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.
  18. ↑ Silventoinen, K.; Rokholm, B.; Kaprio; Sørensen, T. I. A. (January 2010). "The genetic and environmental influences on childhood obesity: a systematic review of twin and adoption studies". International Journal of Obesity. 34 (1): 29–40. doi:10.1038/ijo.2009.177. ISSN   1476-5497. PMID   19752881. S2CID   22339481.
  19. ↑ Herman, Ellen (2008). Kinship By Design. The University of Chicago Press. pp. 155–191. ISBN   9780226327594.

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