Adoption is the closest thing we have to licensed parenting, in most jurisdictions a potential parent is screened by some agency before being allowed to adopt. In situations where one child is adopted and a sibling remains with the biological parent we have the conditions for a natural experiment – a test of the importance of effects of nurture on cognitive ability.
A study published this year analyses 436 such cases. From the paper:
“Individual differences in cognitive ability result from a complex admixture of genetic and environmental influences. Adopted children are one way to estimate the degree of malleability of cognitive ability in response to environmental change in the context of a scientific design that can control for genetic differences among individuals. Sibling pairs in which one member is adopted away and the other reared by biological parents are a particularly powerful research design. In a large population-based sample of separated siblings from Sweden, we demonstrate that adoption into improved socioeconomic circumstances is associated with a significant advantage in IQ at age 18. We replicate the finding in a parallel sample of half-siblings.”
An article (unfortunately behind a pay wall) in the most recent Scientific American examines people with superior autobiographical memory. The article points to evidence that this superior ability to recall life events has a biological basis. This is more evidence that there are real individual differences in memory.
Here is a video about superior autobiographical memory:
Most people think that the question is nature versus nurture. The reality is much much complex and much more interesting.
The current issue of The Observer, a publication of the Association for Psychological Science, includes the following quiz:
- Cognitive ability in the industrialized world “is approximately 50% to 70% heritable,” reports the Tucker-Drob team. This means that
- 50% to 70% of one’s cognitive ability is attributable to one’s genes.
- 50% to 70% of the variation among individuals is attributable to their genes.
- The genetic influence on intelligence scores (heritability) is greatest
- early in life (for example, at age 3), before varied experiences diverge our life courses.
- later in life (for example, at age 50 and beyond).
- The genetic influence on intelligence scores is greatest among those
- at lower socioeconomic levels.
- at higher socioeconomic levels.
- Increasing the quality and availability of educational opportunity serves to
- decrease the genetic influence on intelligence scores.
- Increase the genetic influence on intelligence scores.
You can find the answers here. For a deeper discussion see the original paper.