Chris Stringer is tracing human ancestors back a million years

The more we discover about our species’ family tree, the harder it becomes to pinpoint when exactly Homo sapiens emerged, raising questions over what it really means to be human. “If we look along the sapiens lineage,” says Chris Stringer, a palaeoanthropologist at the Natural History Museum in London, “we see there’s lots of diversity. So it’s not easy to make a cut-off point when we can say, this is Homo sapiens.” Fossils from China may push our common ancestor with Neanderthals back in time, says Stringer. The split is commonly placed at 600,000 years ago, but “the separation may go back even further, towards a million years”, he suggests.