In 2013 scientists excavating a cave in South Africa found remains of Homo naledi, an extinct hominin now thought to have lived 236,000 to 335,000 years ago. Based on the cranial remains, the researchers concluded it had a small brain only about the size of an orange or your fist. Recently, they took another look at the skull fragments and found imprints left behind by the brain. The impressions suggest that despite its tiny size, Homo naledi’s brain shared a similar shape and structure with that of modern human brains, which are three times as large. “We’ve now seen that...