Biology
The Evolution of Human Bipedalism in Paleoanthropology
Quick fact
The oldest unequivocal evidence of habitual bipedalism is the 4.4-million-year-old skeleton of Ardipithecus ramidus, nicknamed 'Ardi,' whose pelvis and foot bones already show a mix of walking upright and climbing trees.
Why this is interesting
You walk on two legs every day without thinking. But why did our ancestors first rise from all fours—and what pushed them to make this the very first step in becoming human?