The human body is amazingly capable…despite the fact that, in many places, it’s engineered all wrong.

Take for example, our lower leg. Our foot has 26 bones, and our ankle, 7. Far more moving parts than needed to walk or run, making us much more prone to injury.

How did this happen?

Well, we evolved from earlier hominins who evaded predators and found food in the trees.

Those ancestors needed a grasping foot, like a chimpanzee’s—with a big toe like an opposable thumb and a flexible ankle like a wrist.

As we climbed down from the trees and onto land, our feet had to evolve.

The foot and ankle became rigid to make a propulsive lever. The arch developed as a shock absorber. The big toe moved forward in line with the others.

This worked well enough. Even though they’re built on an old structure more like hands, our flawed feet carried us into the modern day.

Now, look down at your feet and imagine a different design: a streamlined lower leg wrapped in ligaments, not muscles; a fused ankle ending in one or two large, simple toes with just one bone in each.

Sounds weird—but this is the structure that propels ostriches and horses to speeds over 40 miles an hour, absorbing more stress while using comparatively less energy.

Different structures, borne from different evolutionary pressures.

We’ll look at other curious cases of human evolution in future EarthDates.