For the vast majority of our planet鈥檚 history, there were no humans. Today, there are more than eight billion of us. Logically, then, there must have been a moment when Homo sapiens became a distinct species. Yet that moment is surprisingly hard to pin down. The problem, for once, isn鈥檛 a lack of fossils. Instead, disagreement about when to mark the origin of humanity comes down to the speciation process itself.
We often imagine the human evolutionary tree as a grander version of a personal family tree 鈥� indeed, researchers tend to talk about parent, daughter and sister species. In this picture, our parent species is equivalent to our biological parents, and the birth of H. sapiens becomes an event that is as easy to define as our own birth. But speciation isn鈥檛 really like that.
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For evidence of this, look no further than a study posted online last year. Trevor Cousins and his colleagues at the University of Cambridge suggest our supposed parent species, Homo antecessor, split away from its parent, Homo heidelbergensis, more than a million years ago. About 600,000 years ago, H. antecessor gave rise to two branches: one led to the Neanderthals and Denisovans 鈥� another kind of hominin 鈥� the other to H. sapiens. Then comes the twist. Our evolutionary grandparents, H. heidelbergensis, stuck around to see the birth of the H. sapiens lineage 鈥� and about 300,000 years ago, the two interbred in a big way. In fact, the researchers鈥� model indicates that about .
On the one hand, such studies give us extraordinary insight into our evolution. On the other, they make it ever harder to erect a simple genetic boundary around H. sapiens. Models like this one have even encouraged some researchers, including at the University of Wisconsin鈥揗adison, to argue that almost all these ancient humans belong to our species. If you adopt that thinking, H. sapiens is about a million years old.
The first humans in Africa
That is a minority view, though. A more common approach is to focus on the suite of anatomical features used to define H. sapiens, which include a big, round braincase and a prominent chin. These probably didn鈥檛 emerge all at once. We now know that in Africa, where our species emerged, populations of hominins were constantly splitting, living apart for a time and evolving into potential species with unique features, before mixing and then splitting again. Given this 鈥�African multiregionalism鈥�, we might expect to come across ancient human skulls with modern-looking faces attached to primitive-looking braincases 鈥� which is exactly what has happened.
A few years ago, researchers reassessed a group of roughly 300,000-year-old skulls that had been unearthed in the 1960s at Jebel Irhoud, Morocco. The study showed them to have long, flat braincases 鈥� rather unlike H. sapiens 鈥� but faces that bore striking similarities to our own. Many now see these as the oldest known H. sapiens fossils. That doesn鈥檛 necessarily make them the first humans, however. 鈥淒NA tells us humans and Neanderthals split somewhere in the 600,000-to-300,000-year interval,鈥� says at the University of Nevada, Las Vegas. He thinks our species came into being at the moment of the split 鈥� and the Jebel Irhoud fossils show early evidence of our species after that.
Others take a different view. 鈥淚 think the Jebel Irhoud fossils are on the sapiens lineage,鈥� says at the Natural History Museum in London. 鈥淏ut whether I should call them H. sapiens 鈥� I鈥檓 more cautious.鈥� Instead, he leans towards placing the origin of our species at a more recent time. By about 200,000 years ago, there had been enough mixing and mingling of populations to produce individuals with the full suite of modern anatomical features, as seen in human fossils at a site called Omo-Kibish in Ethiopia. Perhaps it was then that , says Stringer.
One point of agreement is that we have learned a lot about how we became the species we are today. But in doing so, we have inadvertently made it harder to identify exactly when H. sapiens appeared.
This article is part of a special series exploring seven of the biggest chronological conundrums of all time.
Neanderthals, ancient humans and cave art: France
Embark on a captivating journey through time as you explore key Neanderthal and Upper Palaeolithic sites of southern France, from Bordeaux to Montpellier, with 快猫短视频鈥檚 Kate Douglas. Visit iconic archaeological sites and deepen your knowledge of Neanderthals and early human ancestors, all while journeying from Bordeaux across the picturesque south of France. Traverse through charming medieval towns and breathtaking countryside, culminating in the vibrant city of Montpellier.
