In 2013, amateur cavers Steven Tucker and Rick Hunter made a once-in-a-lifetime discovery in South Africa: fragments of bones, including a fossilized human-like jawbone. Now, two years after the fossil was brought to him and he had the cave excavated, Lee Berger, a professor at Johannesburg’s University of the Witwatersrand, believes the area where the jawbone was unearthed is the burial site of a newly discovered species of human ancestor: Homo naledi. These discoveries are so new that the fossils have not ye…