system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Is there a specific reason why our forearms and calves have two bones instead of one?
gpt
It allows them to rotate axially, for example turning your hands from palm down to palm up. Imagine you had one big bone in your forearm - how the heck would that work? You would have to twist the bone itself, and spiral fractures are no fun. Instead, the two bones just shift around each other.