That's an interesting point. Rollers were likely in use long before whels-on-axles, and you could argue that those are basically wheels and partly axles, as they rotated freely from the load, and they do the job of both, but neither as well as an actual wheel on a dedicated axle. It was only when the wheel and axle were separated that we got the full benefit.
this post was submitted on 29 Jul 2026
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But good sir, what use is an axle and wheel without whatever doohicky thingamajig that attaches to a frame that transports things or people?
Not sure if you're serious or not, but wheels and axles are used for a lot more than just transportation. Pottery wheels predate vehicles by about 1,000 years. Windmills and water wheels use interlocking wheels and axles to grind grain. A windlass is essentially just a rope tied to a wheel on an axel for hoisting stuff up, like a bucket in a well.
Not that this matters to the discussion of naturally occurring wheel-and-axle structures. Just an interesting little aside on the value and versatility of wheels.
yep, i don't think there's basically any living organism that is made of two parts that are not solidly attached to another, sothat they can rotate against one another.
knee joint might come to mind, but that's also connected by collagene i think, so it can't rotate by more than 360°.
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.
If your knee can turn 360°, you should talk to some scientists, so that they can study you.
Rotating is in nature, but as you said: always with a maximum rotation, never free without limits.
How about this insect with a pair toothed gears? Not an axle, but still amazing!
"The juvenile Issus - a plant-hopping insect found in gardens across Europe - has hind-leg joints with curved cog-like strips of opposing ‘teeth’ that intermesh, rotating like mechanical gears to synchronise the animal’s legs when it launches into a jump."
it's gears, alright, but i don't think that it can rotate by more than 360°?
No, that's what I meant by not an axle.
But, come to think of it, we can swing our arms round and round, more than 360°.
I would argue that's more due to the up-down and front-back limited rotations combining to form a circular mode, kinda like a Cartesian to Polar coordinate mapping
that's reasonable.
bonus fun fact - the etymology is connected - "axle" comes from older words for "shoulder", or "armpit", which survives in some regional Englishes as "oxter" - the connection is apparently that you'd carry a person by putting their arms up and linking at the shoulders, much like an axle is how wheels carry a cart.
But hedgehogs aren't wheels. There, I said it.
I know at least one that is.
also a lot of animals like going downhill in unconventional ways, such as this one:
(should be a GIF file)
alternative image link:
https://media.tenor.com/aSBOSQUUzhIAAAAM/gliding-penguins-continent7.gif
Not with that attitude
Philip Pullman goes into this a bit in the 3rd book of His Dark Materials.
It is the invention of the differential that is the big deal.
You are correct, nature has round things all over the place. It is like the silly joke who is the first dude to eat a crab? They guy who watch a bird do it.
The differential is a relatively new invention if we consider how long wheels have been around. You didn't need a differential for a 1 wheeled hand cart like a wheel barrow nor for a wheeled drawn behind cart like a horse carriage.
right, even trains don't need diffs, the conic-slice wheels take care of turns fine without.