Eli5: why do the vast majority of mammals walk on 4 legs, while humans only walk on 2?

Question

Eli5: why do the vast majority of mammals walk on 4 legs, while humans only walk on 2?

In: 2

Answer 1

Four legged locomotion requires less brain development and allows for higher sustained speeds in the short term. Humans just cannot outrun most animals, because two legs is slower than four, and we require a complicated cerebellum which requires nutrients and required additional evolution to make happen.

However, two legged locomotion is more efficient than four, allowing dramatically greater stamina. It also allows tool or weapon use while moving. An in-shape human can outlast most prey animals in the long term, briskly walking after them as they run from us, until they simply sit down from exhaustion.