Around two million years ago, our earliest human ancestors experienced an explosive brain expansion, at least one million years after they began to walk upright. Rather than linking bipedalism alone with brain expansion, as previously theorized, Falk’s explanation involves climate. She contends that bipedalism allowed our ancestors to wander farther afield in savannah-like regions, where their brains were subjected to solar heating. Falk and her colleagues discovered that one hominin line developed a complicated brain-cooling system to combat the destructive effects of excessive heat. This ability and expanding brain size evolved together, thus producing hominins with a brain capacity three times greater than their ancestors. Falk further discusses the evolution of visual skills,