alt Hacker NewsHere’s my multiple years of anatomy classes response: the heart isn’t on the left. The aorta is, sure, but the vena cava is on the right. Also people with situs inversus (essentially all organs flipped laterally from “normal”) aren’t obviously more prone to left-handedness.
Replies
> 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.
It might be hard to eliminate confounding factors depending on when the research was done. A lot of people in my generation were still dissuaded pretty heavily from writing with their left hands. I'm not entirely convinced anymore as a lay person that "handedness" is a real, distinct phenomenon that's primarily genetically determined or a result of the organization of the brain. It's equally possible that it's a learned preference and that the way the brain organizes around it is as a result of the preference's impact on how you have to solve problems with your preferred hand in a society that preferences right-handedness.
Not disagreeing that handedness is probably unrelated to heart position.
But why would situs inversus somehow be tied to this at all? If there's a gene that favors right-handedness, it's not like it would somehow "choose" left-handedness because the individual has their internal organs flipped.
>Here’s my multiple years of anatomy classes response: the heart isn’t on the left.
Why is the left lung smaller, then?
I’ve wondered ever since fourth grade (where an anatomical model in a corner of the classroom always made it clear that the heart is centrally located) how the vernacular conception of the heart as located on the left originated and persisted.
Your post finally made it click for me – the aorta extending to the left gives the superficial impression of that being the heart’s location because it’s easier to feel the heartbeat through the skin, versus the more deeply embedded vena cava on the right.
Presumably this means, evolutionarily, greater vulnerability on the left, predisposing the left hand to shielding duties, leaving the right to more dexterous tasks like spearing. The cardiological hypothesis of right-handedness holds!