In a fossil first, researchers have announced the discovery of 1.5 million-year-old footprints that prove two different pre-human species coexisted in Kenya. The tracks hint that the species may have interacted, raising new questions about the behavior of our ancestors.
"I would expect the two species would have been aware of each other's existence on that landscape, and they probably would have recognized each other as being 'different,'" Kevin Hatala, a paleoanthropologist at Chatham University in Pennsylvania, told Live Science in an email.
