More than three million years ago, a distant cousin of ours called Australopithecus afarensis was walking around on two legs—making the species a key chapter in the human story. But a new study of a rare A. afarensis toddler suggests that the species' feet retained some apelike traits, perhaps helping them climb trees.

The study, published in Science Advances on Wednesday, takes a close look at the foot of Selam, a 3.3-million-year-old female A. afarensis that died before the age of four. The fossil helps scientists see how A. afarensis feet changed from birth to adulthood, which in turn lets us glean some details about how they grew up.

“We can understand what was going on in the young individuals