> > The most surprising result for me is that across all the traits they compiled, the heritability is 49%. Which is much much lower than I would have expected.
> But much much higher than almost all people would believe.
People's casual usage of the term heritability doesn't match the way it's used in scientific contexts. For instance, people wouldn't normally say that the trait of "being a slave" is explained by genetics, but the heritability (in the technical sense) of being a slave in the mid 1800's USA was rather high.
> but the heritability (in the technical sense) of being a slave in the mid 1800's USA was rather high.
No, it wouldn't be. Monozygotic black twins would have the exact same chance as dizygotic black twins of being slaves, and slavery would cluster in families, with whole families tending to be free or slave, leading to very high shared/nonshared environment estimates.
Actually, "heritability" in the scientific context can be counterintuitive sometimes. I'd bet that the heritability of slavery in the 19th century was actually pretty low - I wouldn't imagine that monozygotic twin pairs are any more/less likely to be be slaves than same-sex dizygotic counterparts. Indeed, the majority of variation of the "is a slave" phenotype would be due to environment as slaves get set free.
Think of a trait like hair colour in East Asians. Having black hair is completely determined by genes, but heritability is pretty much zero since (with maybe a few extreme exceptions) variation in hair colour in that population is entirely environmental (use of hair dyes, etc.). In Europeans however, heritability is probably much higher due to greater variation in hair colour.
People's casual usage of the term heritability doesn't match the way it's used in scientific contexts. For instance, people wouldn't normally say that the trait of "being a slave" is explained by genetics, but the heritability (in the technical sense) of being a slave in the mid 1800's USA was rather high.