“What does it mean to say IQ test scores are largely genetic? Does this make you think that differences among IQ scores between races are genetic?” Starting with these two questions, I aim to get an audience of high school students thinking about the three areas that make up this sequence of posts. Comments welcome about how to revise this approach so as to provide a “conceptual starter kit for thinking about genes, race, and IQ test scores.“
A. First question, “What does it mean to say IQ test scores are largely genetic?” (asking for audience input and filling in the following sequence of answers and “buts”)
1. Genes cause IQ more than environment does. But how to separate these—everyone also needs an environment to survive and grow.
2. If your parents are above-average IQ, you are more likely to be above average. But parents also pass on environment (educational options, etc.)
3. Differences in genes from one person to the next have more influence on IQ than differences in environment. But how do you track the influence of genes without knowing which of our 30,000 genes influence IQ, and even worse for environmental factors.
4. If you and your identical twin were separated at birth and raised in difference families, you’d be more similar than any two random people raised in different families. But these situations are very rare (and not necessarily at birth and not necessarily in independent families).
5. If your sibling is adopted into a professional family but you grow up poor and you end up with same IQ. But this is not on average true—usually there’s a strong boost in IQ for the adopted child.
6. Identical twins raised in the same family are more similar on average than non-identical twins raised in same family. Remember, identical twins share all their genes, but non-identical do not, so the increased similarity corresponds to sharing more genes. This answer seems better (although not without critics). It is on this basis researchers say IQ has a “heritability” of 60-80%.
(Note: Here heritability is a technical term with a quite different meaning from the idea that something is heritable if there is a gene that gets transmitted from parent to offspring.)
Continued in the next post.