Nature creates round objects all the time (stones in a river, a hedgehog in a ball,…), but the principle of an axle is not found as far as I know.
Nature creates round objects all the time (stones in a river, a hedgehog in a ball,…), but the principle of an axle is not found as far as I know.
I think the bivalve style is the more interesting case—it’s like their guts have a built-in mortar-and-pestle.