A generation or two ago, adoptive parents (at least adoptive parents of infants) were told that their children were a blank slate. There would be no “embarrassing” sharing of medical or social information from the birth family; that was irrelevant. It would be as though the child was born to the family.
Then science began to validate that many more illnesses than previously believed had genetic roots, and that many behavioral problems and mental illnesses had physical roots. Researchers began to study identical twins separated at birth, siblings raised with their birth families, and birth parents of children adopted at birth. Many of these studies claimed to show a high correlation, of I.Q. scores and of traits measured by personality questionnaires, between adopted children and the birthparents they had never met. Adoptive parents—and their well-meaning relatives who wanted to “spare us heartache”—began to fear that they would not be able to substantially influence who their children would become.
What does the research really say? Well, it’s not conclusive—but there are some points to keep in mind. First, most statistics refer to groups, not individuals. Height may be a largely heritable trait, but individuals and groups whose nutritional status changed dramatically are often substantially larger than their parents. Even if I.Q. were found to be highly inheritable, it cannot predict an individual child’s score.
A 1978 study in Minnesota found that a group of children whose birthparents’ I.Q. scores predicted a mean group average of 101 (100 is average), but who had been adopted into families of high educational motivation and relatively high socioeconomic status, achieved I.Q. scores six to nine points higher than their birthparents’ scores would predict.
A 1989 study compared four groups: children born to families of low socioeconomic status (SES) and adopted by families of low SES; children born to families of low SES but adopted by families of high SES; children born to birthparents of high SES who were adopted into families of high SES; and children born to parents of high SES who were adopted into families of low SES. The authors found that children raised in families of high socioeconomic status scored 12 points higher than children raised in families of low socioeconomic status. However, children born to parents of high socio-economic status scored 15 points higher than children born to parents of lower socio-economic status regardless of adoptive family.
The authors conclude, “Although these findings clearly indicate that the biological parents’ background contributes to observed differences in I.Q. between extreme groups, as does that of the adoptive parents, more detailed interpretation is difficult.”
The authors also note that, while the adoptive parents’ contribution was clearly environmental, the study cannot differentiate how much of the birthparents’ contribution was due to genetics and how much to prenatal care.
More recent research also claims that early intervention services (usually meaning birth to three or birth through preschool services with educators, speech and/or motor therapists) can increase I.Q. points by an average range of six to ten points.
Mental illnesses like schizophrenia are perhaps among the worst fears of adoptive parents. A study in Finland in 1987 studied 59 children of schizophrenic birthmothers who were raised by adoptive parents. Ten of these adopted children were mentally ill. Eight of these ten had schizophrenic birthparents and non-schizophrenic adoptive parents. Initially this was considered evidence of overwhelming genetic influence. However, the researchers delved further and discovered that nearly all of these mentally ill adoptees had been raised in troubled families. None of the 49 children raised in families judged “healthy or only mildly disturbed” were diagnosed as schizophrenic, psychotic or borderline. (Three children–six percent–were noted to have milder mental or emotional problems.”) It seemed that a genetic vulnerability to schizophrenia required an unfavorable environment to become clinically manifest.
Unsurprisingly, the studies show that both genes and environment are important, and it is difficult to pin down the relative influence of each. Nonetheless I believe these findings are encouraging to adoptive families.
Please see these related blogs:
What Really Happens When Adopted Children Grow Up?
Does Research Validate Our Fears?
Does Research Validate Our Hopes?