We arose in Africa: no argument there. Now a new theory challenges the standard one that humankind arose from one place in Africa, from one group. The awkward fact is that accruing archaeological and genetic evidence doesn’t support the single-point-of-origin linear-progression hypothesis.
Archaic Homo sapiens remains have been discovered from Africa’s north to its south. They were all over the place. So a vast international team of scientists is proposing a new paradigm, in a paper published Wednesday in Trends in Ecology & Evolution: that humans evolved across the continent. They lived in partial isolation and thus developed local morphological distinctions.
If it sounds odd that Homo sapiens could develop throughout Africa rather than spring, Venus-like, from one spot, and if it sounds odd that they had local divergences, think of zebras, lions or African elephants. All today exist in local varieties, but are clearly zebras, lions and elephants. Distant groups of early Homo sapiens scattered around Africa would still have been Homo sapiens, but likely have developed local traits.
That in turn would explain why archaic Homo sapiens fossils evince morphological diversity.
The genetic evidence also suggests that early humans mixed with other hominin species as well – but that’s another story.
Is it Adam?
Part of the confusion about our origins is because archaeologists don’t necessarily agree that a given archaic fossil is Homo sapiens. There is no consensus on which characteristics are human/non-human.
“The species concept is a heuristic. It’s not like one day we were archaic and the next we were sapiens,” lead author Eleanor Scerri of the Oxford School of Archaeology explained to Haaretz.
“Homo sapiens began to split off from the common ancestor we share with Neanderthals about half a million years ago, so this is the earliest glimmerings of our species,” Scerri says. The earliest sapiens wouldn’t necessarily have looked or behaved anything like us.
The splitting process – before we began to look and behave like we do now – took about 200,000 years. “If you went back in time half a million years, you wouldn’t necessarily see anyone who behaved or looked like us,” she says. Even the first sort-of-recognizable sapiens would have looked very different from us.
For decades, based on the evidence available at the time, archaeologists assumed human evolution began in eastern Africa around 200,000 years ago. Then anomalies started to crop up.
A skull found in Jebel Irhoud, Morocco, was dated to more than 300,000 years . A skull found in Florisbad, South Africa, is 260,000 years old. This year, archaeologists found a nearly 200,000-year-old sapiens jawbone in Israel.
True, archaeologists are still arguing whether or not the above were sapiens, habilis or some other species. Some even classified the South African skull as a new species called Homo helmei, but still agreed it was an archaic form of sapiens.
The team doesn’t embrace the Homo helmei theory. “The prime reason for that is because we see this mix of archaic and modern features in different combinations and in different places for a long time – up to 11,000 years ago,” says Scerri. “So it doesn’t make sense to filter out all these earlier fossils, especially when they behave in very modern ways, which we can see from the archaeology.”
Not necessarily a throwback
The fossil record shows a continent-wide trend toward the modern human form, in short. “The fact that these features appear at different places at different times tells us these populations were not well connected,” Scerri says. “This fits with a subdivided population model in which genetic exchanges are neither random nor frequent.”
The team also believes that rather than being some linear progression, over the hundreds of thousands of years, human evolution was “mosaic-like.”
What they mean is that some archaic humans evinced certain modern traits and other archaic humans had different modern traits. (Not that people agree what being “human” is, but bear with us.) One group might have had a rounder cranium, another sapiens-like jaws, a third our spectacular chin, and so forth. It was all mixed up, Scerri suggests. This suggested there was a continent-wide trend toward the modern human form that involved all these different populations.
The mixing eventually eliminated the archaic characteristics and brought the modern characteristics together, thus making us look like we do today, she sums up.
“Irrespective of the persistence of archaic features quite far into recent times, behaviorally and ecologically, we were clearly modern by 300,000 years ago,” Scerri adds. Everything being relative.
Over generations on end, physical barriers – from rivers to mountains to forests and desert – came and went. For example, just when early humans were there, Saudi Arabia had rivers and hippos. There would have been ample opportunity to mix, and not to mix.
The new theory of intermittent mingling of subpopulations from the southern tip of Africa to the continent’s northern coasts fits much better with the fossil and genetic data than a single population model, the team sums up.
OK. But the Homo sapiens scattered across Africa had to come from somebody. Scerri suggests they stemmed from an ancestral hominin who was already scattered across Africa. It didn’t have a single point of origin, either. You might find it useful to think of elephants again.