Stone Age men, so the story goes, got the wheel inspiration by observing trees rolling downhill. So they sliced trees and fit the rounds they got to their sleds, to move them faster and with less effort. In so doing, they also invented carts while expediting transportation.

But friction’s thermal side effects caused the wheels to wear down quickly, which required more effort to cut down more trees. So the clever Stone Age men thought to slow the wheel’s velocity by making it square, which meant it could also be cut from stone, a lot more durable than wood. The first velocity trials went all right, but when the wheels moved into mass production, there were customer complaints: The ladies traveling on the carts disliked the frequent bumps a four-sided wheel produced.

By this time, our Stone Age ancestors had also become engineers. Because the wheel’s square shape produced four uncomfortable bumps for passengers, our inventive ancestors reduced that number to three by giving the wheel a triangular shape. But that proved too much, even for these rough, tough people, so they went back to the original round shape.

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