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Comment by lvoudour | Hacker News Reader

What would be the evolutionary pressure to grow wheels? They are useless without roads

Roads, i think you answered your own question, would be an evolutionary pressure, hypothetically speaking.

I sometimes imagine wheeled creatures evolving in a location with a big flat hard surface like the Utah salt flats or the Nazca desert, but I guess there's not much reward for being able to roll around since those places are empty as well as flat. Tumbleweed found some success that way though, maybe?

Is there any biological examples of freely rotating power systems? We have nice rotating joints with muscles to provide power, but I can't think of any joint that would allow the sort of free rotation while also producing torque, a wheeled animal would require.

Something internal to some shellfish, I believe, a kind of mixing rod that rotates. Hold on, I'll check if it's powered. (Also rotifers but they're tiny.)

Hmm, no, it sounds like it's externally powered:

> The style consists of a transparent glycoprotein rod which is continuously formed in a cilia-lined sac and extends into the stomach. The cilia rotate the rod, so that it becomes wrapped in strands of mucus.

https://en.wikipedia.org/wiki/Rotating_locomotion_in_living_...

Or maybe the cilia ( = wiggly hairs) could be seen as a kind of motor. Depends how you count it and exactly what the set-up is, I can't tell from this.

I think I would count internal power created by the rotating component itself. I hadn't though of that possibility, since human made machinery usually has the power producing component located in the main body and transferring that power to a freely rotating component is quite hard. Biological systems wouldn't necessarily look like that, and could feasibly be powered by the wheels themselves deforming as if the wheels were a separate, but connected, biological system.

That's quite interesting.

Some microorganisms have cilia that rotate like a propeller. With complex molecular structures to provide a rotor effect

The golden wheel spider lives in the sand dunes of the Namib Desert. When confronted by a spider-hunting wasp, it can perform a "cartwheeling" maneuver to escape. By tucking in its legs and turning onto its side, it can roll down a sand dune.

Humans can also do this, sometimes they use tools like a tractor wheel to conver themselves into downhill wheels, often to hillarious effects.

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