第38期:非洲大裂谷

Along the African coast, a great rift opens up. It stretches nearly 4,000 miles, with mountains growing along its edge.

This ape-like creature may stay in these trees forever, but its world is changing. The growing mountains act like a wall, prohibiting moisture from the Indian Ocean from passing over the land.

It's getting hotter, and drier. The lush rainforest becomes an arid savannah.

The new hotter climate changes the creatures' habitat , forcing them to search further for food, soon, they stop dragging their knuckles like apes.

And begin to stand, and walk on two feet. It's the most important step in the human story.

This mountain range could be the reason humans walk on two feet.