The story of human evolution has just become more complicated. Spectacular fossils from in the Rising Cave system in South Africa are compelling us to consider what it means to be human. They are radically changing our understanding of evolution by revolutionizing our human family tree.
In 2015, the discovery of a new human ancestor stunned palaeontologists across the globe.
Headlines lauded the work for rewriting our history; for filling gaps in the evolutionary record, while others claimed it had the potential to upend everything we know about our cultures and behaviours.
This new species christened Homo naledi, was an unusual mix of the old and modern. Their heads were small, suggesting an early hominin perhaps more than a million years old. But their feet were stiff for walking upright and their hands adept like modern humans.
In the media frenzy that followed—a National Geographic cover, a documentary, numerous articles—the question kept coming up: How old are these Homo naledi fossils, really? What do they tell us, if anything, about the origin of Homo sapiens?
This week the answer to the first question was revealed: 236,000 to 335,000 years old.
The second answer provokes more questions because it suggests more diversity in Africa than previously thought. Our early ancestors did not simply become bigger brained and more upright over time. They also begat other lineages—Homo naledi is an example; Homo neanderthalensis in Europe is another—of which modern humans are the only extant branch.
“You can’t tell simple stories anymore,” says Prof Lee Berger, the paleoanthropologist at the University of the Witwatersrand who led the research. “The idea that you have this single lineage, this one line from Lucy all the way to homo habilis, homo erectus and onto humans, that just isn’t a viable hypothesis anymore. It’s a very bushy evolutionary tree.” And Homo naledi is the new addition to the human family tree.
The discovery that another hominin, so different from us, lived as recently as 236,000 years ago, adds more mystery to the question of why humans are the only surviving members of this once diverse family.
It was thought only Homo sapiens existed in Africa during this period (the late Middle Pleistocene).
More critically, it is at precisely this time that the fossil record shows the rise of what has been called “modern human behaviour” in southern Africa – behaviour attributed, until now, to the rise of modern humans and thought to represent the origins of complex modern human activities such as self-adornment and complex tools.
It’s still too soon to know exactly how we’re related to Homo naledi and why we survived but they didn’t. Whatever the answer, it will force us to consider what it means to be human.
Berger’s team of forty collaborators from around the world address these answers in three new papers published this week via open source in the journal eLife.
The first paper provides the age of the original fossils. The second announces the discovery of a second chamber in the same South African cave system, containing over 130 Homo naledi fossils including a nearly complete skull. The third and most speculative paper takes up the question of how Homo naledi evolved and revisits a controversial hypothesis for the presence of these fossils in the cave.
Why not join our Archaeology tour that visits The Cradle of Humankind World Heritage Site where you’ll see the original 2015 specimens in the largest display of original fossil hominin material in history, that forms part of an exhibition called Almost Human, as well as meet with Lee Berger and some of his groundbreaking team.
Acknowledgment: Sarah Zhang – TheAtlantic.com; Victoria Woollaston – Wired.co.uk; Dr Tracy Kivell – the University of Kent.