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.
Wikipedia has a whole article on this subject:
https://en.wikipedia.org/wiki/Rotating_locomotion_in_living_systems
The exceptions it mentions are bacterial flagella and part of the digestive system of some bivalves.
yeah thanks for the article! rotating bacterial flagella is what came to my mind as well, but it’s microscopically small (i think the flagella is a single macro-molecule?) so i’m not sure whether to include it in the list of (macroscopic) “mechanical rotation”… it’s more like biochemical mechanical rotation.
if we go for biochemical mechanical rotation, there’s more: ATP-Synthase is a molecule that sits in cell membranes and that rotates as well each time that a proton passes through it.
I think the bivalve style is the more interesting case—it’s like their guts have a built-in mortar-and-pestle.