alt Hacker News> Also people with situs inversus (essentially all organs flipped laterally from “normal”) aren’t obviously more prone to left-handedness.
I feel like this isn’t really an argument against the theory. If right handedness did evolve because of heart position, a later genetic mutation to have the heart on the opposite side wouldn’t suddenly undo the previous evolution towards right handedness.
Why are you assuming situs inversus, which occurs in species with no handedness (or, indeed, hands) came after handedness?
The argument is that the selection bias was towards precision and the hypothesis was that precision is influenced by heart position (which is, still, in the middle in humans)… individuals with situs inversus would be more precise in the left hand, thus if the causal hypothesis is correct AND the argument holds then there should be a selection bias that would result in a correlation between situs inversus presence and left-handedness.
In the end I don’t believe either the argument or the hypothesis hold even as much water as I can in either hand.