The oldest distinguishing feature between humans and our ape cousins is our ability to walk on two legs—a trait known as bipedalism. Among mammals, only humans and our ancestors perform this atypical ...

WASHINGTON — Ardi lived 4.4 million years ago in the woodlands of East Africa. She spent most of her time in the trees. She stood about 4 feet tall, weighed 110 pounds, and had long arms, short legs ...