Why don’t horses have wheels?

Published on October 4th, 2011
Why don't horses have wheels?

Nature is full of amazing creatures. For most of human history, there was very little we invented (in terms of technology) that hadn’t been seen in other animals first.

But one invention – the one we often think of as our very best one, what with its use in transport and mechnical gears and so on – has never been seen in the animal kingdom.

That invention is the wheel.

Why are there no wheeled horses leaving their less roadworthy cousins in the dust? Or crayfish popping wheelies at the bottom of the ocean?

Well, one reason is that wheels aren’t actually all that useful for most animals, not even for transportation. The wheel for transport is only really functional in a certain type of environment – fairly flat, hard roads. Take them off-road (as the wilds tend to be) and they’re far less helpful – an animal with wheels for legs would have a very difficult time climbing a mountain, or even a hill, and would find it hard to control its speed on many surfaces.

Another reason is that it’s not really possible – or, at least, not easy – to evolve a wheel-leg, at least not one with a living wheel that’s attached to the rest of the body. Think about it – where would the blood vessels go? And the nerves? And what would happen to them when the wheel started turning? It wouldn’t be a pretty sight.

Of course, nature doesn’t take a challenge like that lying down: having realised that a big wheel isn’t feasible, it decided to do some nano-engineering. In fact, even though it took us a long time to see it, nature has had wheeled creatures for over three billion years.

Many types of bacteria – yes, those microscopic critters that are everywhere, and that have dominated the Earth pretty much as long as there’s been life on it – have a tiny flagellum, a whip-like structure that they use to propel themselves forward. The base of the flagellum fits into a little wheel (see the diagram on the right) which can rotate freely thanks to molecular forces.

Seems Mother Nature has us beaten again. But maybe one day we’ll outsmart her…