2017 Evolution Review

The story of humans’ origins got a revision in 2017
Homo sapiens’ emergence pushed back to around 300,000 years ago ¹

Human Evolution Timeline Topples
Our ancestors’ origin story is being refined. ²

“The most important thing for a reader to take away from this, and also for young scientists in general, is that we don’t have all the answers,” Holen says. “That’s why we do science." ³

For decades, schoolchildren across the globe were taught our origin story went something like this: An archaic form of Homo sapiens evolved around 200,000 years ago in Africa. By about 100,000 years ago, the population had become anatomically modern humans who, around 50,000 years ago, headed across Eurasia and met up with our distant cousins the Neanderthals (and the closely related Denisovans, not known to science until 2010).

Like a game of Jenga, however, researchers have recently been removing bricks and destabilizing that towering timeline. In 2017, a few more bricks came out, and the conventional chronology of our origins finally toppled. ⁴

During a June news conference, shortly before the study was published in Nature, Hublin noted it’s unlikely the Jebel Irhoud individuals, the oldest known Homo sapiens fossils by about 100,000 years, are our direct ancestors.

“We are not claiming that Morocco became the cradle of modern humankind,” Hublin says, “We think early forms of humans were present all over Africa.” ⁵

And in the journal Science in late Septem­ber, a separate team offered additional evidence of an earlier start date for our species: By sequencing the ancient DNA of seven individu­als from southern Africa, the researchers determined modern Homo sapiens emerged up to 350,000 years ago.

For years, paleogenetic studies have been turning up hints that our species interbred with Neanderthals and Denisovans between 40,000 and 100,000 years ago. A Nature Communications study published in July, however, found evidence the hook-ups began much earlier: roughly 220,000 to 470,000 years ago.

Researchers extracted maternally inherited mitochondrial DNA (mtDNA) from a 100,000-year-old Neanderthal bone found in a German cave in the 1930s. The mtDNA is from a Homo sapiens female who evolved in Africa — our homeland — and mated with a European-evolved Neanderthal at least 220,000 years ago. ⁶

A pair of partial hominin skulls excavated in Xuchang, China, are unlike any others. Dated to more than 100,000 years old, the crania have a unique blend of features: the internal ear structure and back-of-skull depression seen only in Neanderthals, which have never been found east of Siberia; a low and broad shape consistent with earlier East Asian hominins; and an enlarged braincase similar to other late archaic and modern humans.

Trinkaus and colleagues, describing the partial skulls in March in Science, won’t speculate on whether they belonged to Homo sapiens transitioning from archaic to modern, the elusive Denisovans or an as-yet-unidentified hominin species. ⁷

The conventional timeline placed our species in Australia at no earlier than about 47,000 years ago, despite some archaeological and genomic research hinting at a much earlier arrival date. In July, however, a team reported in Nature that thousands of artifacts from a Northern Australia site were about 65,000 years old.

And in August, also in Nature, a separate team reported that they believe teeth found in an Indonesian cave belonged to anatomically modern humans who had occupied the site 63,000 to 73,000 years ago.

That puts modern humans far from home tens of millennia before the now-outdated human evolution and migration timeline had us even leaving Africa. ⁸

A Nature study published in April made a startling claim: Rounded stones found beside fractured mastodon bones near San Diego were evidence of  someone [italics theirs] processing the animal’s remains 130,000 years ago.

The current timeline for humans arriving in the Americas, however, is a mere 15,000 to 20,000 years ago, via Siberia and the now-submerged land bridge Beringia. Many in the field are highly skeptical of the Nature paper. ⁹

For example, the Jebel Irhoud crowd lived during a period when possibly several African Homo species acquired unexpected mixes of skeletal characteristics reminiscent of even earlier Homo species and of people today. Witness the patchwork quilt anatomy of Homo naledi. This unusual-looking hominid, known from fossils from South African caves, lived between 335,000 and 236,000 years ago, researchers announced in June (SN: 6/10/17, p. 6). That estimate came as a surprise: H. naledi’s orange-sized brain and curved fingers resemble those of Homo species from around 2 million years ago. But many other features of H. naledi — possibly including a brain organized for social emotions and advanced communication (SN Online: 4/25/17) — could pass for those of Neandertals and humans. ¹⁰

Hominin Trackways in Greece? The Game Is Afoot
Fossilized footprints may change our family tree. ¹¹

And in an analysis published in August, researchers concluded — controversially — that these footprints at Trachilos, Crete, appear to belong to a hominin, walking where none was thought to set foot until millions of years later. ¹²

For example, Harcourt-Smith notes that bears, whose hind legs do not typically make claw impressions, were present in this region at the time, but the team compared the prints with only a bear’s forelimb. The lack of claws is one of the traits cited by the authors as evidence a hominin made the prints.

“Bears do rear up and move bipedally on occasion,” Harcourt-Smith says. “I’m not saying that’s what this is, but it was a major omission not to include hind leg bear prints for comparison. ¹³

“Some people have suggested that we are driven by a Eurocentrism claim. We are making no claim whatsoever,” says Ahlberg. “It’s clear modern humans evolved in Africa.”

Instead, he says, the Trachilos prints show at least one branch of early hominins was present in Europe, and that members of our family tree were walking efficiently on two legs more than a million years earlier than we thought. ¹⁴