Ah, families are so complicated. You think you’re clear about who is related to whom, and then a long-lost relative surfaces and it all gets hazy again.
That’s the current situation with the evolutionary family tree of every one of us. The discovery four years ago of a new member of the Homo genus—that means humans, of which Homo sapiens is the only surviving member—created a fresh puzzle in the story of human evolution. And now a new family member, called Homo naledi, is proving even more disruptive. According to the latest results on H. naledi skeletons and bones, remarkably well preserved in a cave in South Africa, the species may be far younger than was suspected. These slight beings could still have been living around 250,000 BC. The earliest known anatomically modern humans in Africa date back to around 200,000 years ago, and so something like big-brained Homo sapiens would have coexisted with these smaller, more “primitive” creatures.
Primitive, perhaps—but their discoverers think they might have elements of a Stone Age culture, including burial and tool use. Regardless of whether that theory pans out, the new fossils seem likely to supply one of the biggest shake-ups in human evolution for several years, comparable to the discovery of the diminutive Homo floresiensis (the so-called “hobbit”) on the island of Flores in Indonesia in 2003.
These and other discoveries in the human fossil record show that we can’t any longer think of our having evolved in linear, sequential fashion from steadily less ape-like ancestors. Instead, there seem to have been several very different-looking groups of humans living alongside one another—and perhaps even interbreeding. We already knew that was so throughout most of the last ice age (since about 100,000 years ago), when humans coexisted with Neanderthals and another subspecies of Homo called Denisovans identified from fossils in Siberia. But now it appears that various types of Homo lived side by side for far longer.
The new results are published in three papers* in the journal eLife by palaeoanthropologist Lee Berger of the University of Witwatersrand in Johannesburg and his coworkers. They describe 130 H. naledi fossils, including an almost complete (probably male) skeleton dubbed Neo, found in a second underground chamber within the Rising Star cave system in which the…