What we know about human evolution may soon be turned on its head

THE idea goes that modern Homo sapiens — that’s us — evolved as an isolated community in Africa some 500,000 years ago. We then upped tools and trekked across the world, pushing Neanderthals aside as we went.

Turns out, that may not be quite right.

No, we’ve not found the imposing black monolith from the famous 2001: A Space Odyssey.

But some recent finds are no less significant.

“A few years ago, it seemed all too easy,” writes University of New South Wales Dr Darren Curnoe. “The matter was settled. Homo sapiens had evolved in the East African rift valley roughly 200,000 years ago and exited the mother continent to settle the remaining planet around 60,000 years ago.

“As someone who’s kept a keen eye on developments in, and indeed actively researching, our evolution, it’s clear to me that there’s something’s going on here. Change is in the wind!”

Part of this upset of established ideas is a new discovery in China.

On the cliff face in the north-central China state of Shangchen, a scattering of stone-age tools have been recovered.

They’re more than 2 million years old, their discoverers report in Nature.

Until now, the oldest known evidence of human ancestors — in this case Homo erectus — outside Africa was in Georgia, Eastern Europe. That dates back to about 1.85 million years — almost immediately after the species appeared in Africa.

But 96 stone blades, flakes and cores used to carve up antelope, deer and pigs in China’s Loess Plateau has upset the timeline.

They indicate hominins — the family that includes humans and our ancestors — got out of Africa at least a quarter of a million years earlier than thought, and occupied Shangchen on and off for more than 850,000 years.

Now, one argument goes, this indicates one of our more adventurous ancestors - Homo erectus - did not itself evolve in Africa.

Instead, Homo erectus is possibly an amalgam of diverse branches of earlier homominims that had already spread through Africa, Europe and Asia.

It’s an idea that emerges even as the origins of ourselves - Homo sapiens - falls under the spotlight.

EARLY ADAPTORS
More than two million years ago, our ancestors appear to have already conquered the world.

The new finds suggest this was at least 250,000 years earlier than previously thought.

Geologist Zhaoyu Zhu of the Guangzhou Institute of Geochemistry at the Chinese Academy of Sciences was careful. He spent years checking and rechecking dates for the layers of sediments in which the tools were embedded.

Study co-author Professor Dennell of the University of Exeter said: “Our discovery means it is necessary now to reconsider the timing of when early humans left Africa”.

Previously, the oldest evidence of hominin activity in Asia were fossils and stone tools dating back between 1.5 and 1.7 million years. This includes part of a Homo erectus skull found just 4km from the new tool site.

Despite pushing back the date of hominid expansion, it also indicates they were much more hardy than believed.

The site in which the long-term settlement was found had experienced severe temperature fluctuations during that time — from intense heat to freezing cold.

And while early hominins had not yet evolved our long legs, bigger brains nor developed advanced tools such as hand axes — they thrived.

There is as yet no evidence of the exact hominid species that produced the Shangchen stone tools. In fact, if made by Homo erectus, it would mean the species evolved in China before it did Africa.

This adds fresh weight to what has until now been a fringe theory: that a more primitive species of hominin than Homo erectus had escaped Africa much earlier — and that Homo erectus evolved in Eurasia, later to recolonise the homelands of its forefathers.

FAMILY TREES
Dr Curno writes that other recent discoveries indicate our species — Homo sapiens — first emerged in Africa some 315,000 years ago. They appeared in southern China some 139,000 years ago.

We know from genetic analysis that, along the way, we interbred with Neanderthals. We cavorted with a mysterious second species — the Denisovans. And there may have been a third, as yet unidentified, romantic interlude.

Even so, the makeup of Homo sapiens is looking somewhat complex.

“We’ve also begun to find humans whose physical traits don’t fit with our preconceived notions of what sapiens should look like, such as the Iwo Eleru, Nazlet Khater and Red Deer Cave people surviving quite late in various parts of Africa and in Asia,” Dr Curno says.

“So profound is the shift underway in human origins science that it’s seen the unusual step of a team of 23 researchers … publish today’s new synthesis of the evidence — and in doing so embrace the emerging picture of complexity and ditch the old simplistic ideas.”

He’s referring to another new study, led by Eleanor Scerri of the University of Oxford, published in the journal Trends in Ecology & Evolution:Did Our Species Evolve in Subdivided Populations across Africa, and Why Does It Matter?
Here, the researchers argue we did not evolve from a single population from a single region of Africa.

Instead, we’re a hybrid of separate hominid populations that had spread out only to merge into one new species much later.

ORIGINS OF US
We know that Neanderthals and Homo sapiens began to diverge from a common ancestor about half a million years ago.

Only around 300,000 years ago did early homo sapiens (people) actually begin to have features that made them look like humans, Dr Scerri said.

But, even then, “all the fossils between 300,000 years ago and about 100,000 years ago don’t really look like anyone living today,” Scerri told Live Science.
Some populations had small faces. Others had prominent chins. Still more had globular skulls and small teeth.

But, while common to all of us now, none of these features were then found in a single individual.

“These features tend to be distributed across the early fossils in different combinations with different, what we call, more primitive or archaic features that we don’t see in anyone living today,” Scerri says.

It was only through occasional meetings between different groups between 100,000 and 400,000 years ago that brought all these modern traits together.

“Which means, of course, that evolution probably progressed at a different speed and tempo in different regions of Africa as different groups came into contact with each other at different times,” Scerri says.

Dr Curno says this raises the question: what is a Homo sapiens anyway?

“Does this mean they aren’t our forebears? Not necessarily, just that our current approach is pretty limited and we need to keep in mind that our earliest ancestors would have looked, well, ancestral!,” he writes.