> - 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.
But much much higher than almost all people would believe.
For example, if you were to sort the population the length of their pinky finger, and then look at two groups of people, one the longest-pinky quintile and one the shortest, there is nothing in this study that would suggest those two groups would have different resting heart rates. This is true even though we can assume on the basis of this work that both pinky length and resting heart rate are about 50% heritable.
The only way they would be correlated would be if there was a single selection mechanism for both, and given that visible traits and non-visible traits tend to have completely different selection mechinisms you'd have to show positively and directly by experiment that such a common mechanism existed in any given case.
Ab initio there is simply no basis for the claim any random non-visible traits like resting heart rate will have different group averages for groups that are segregated from the general population by any random visible characteristics like pinky length.
Genetic similarity is the "master mechanism that would correlate the group average of one trait with another."
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.
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.
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.