Homologies are characteristics inherited by common descent. The more homologies two organisms have, the more recent their common ancestor. We share hindcannons with horses and Hox genes with the Mayfly, (which makes literal heads or tails of our bodies.) We have the vertebrae of a Jerry-rigged quadruped. Our facial nerves follow odd, torturous routes around our skull. These paths don't make sense in humans, but they do in sharks.

Tiktaalik is a large shallow water fish that lived 375 million years ago. The bones in its front limbs have the beginnings of a wrist. All wrists owe their existence to this arcane amphibious creature.

Our body is an evolutionary roadmap. Your elbow? It's 15 million years old. Your tooth pattern? That's 35 million years old. Your knees? You're looking at 1.8 million year old engineering. Listen to your body and it will tell you the story of life on Earth.