Digital DNA

Oldest Human DNA Found Could Rewrite Evolutionary History

Scientists have sequenced the oldest human DNA found in a fossil dating back about 430,000, and the results have them curious about a population of human ancestors that lived between 700,000 to 900,000, shattering the previously held consensus that it was sometime between 100,000 and 50,000 years ago, that Homo sapiens migrated from Africa in search of new exploits. The extraordinary new find could push back the time when our ancestors are believed to have split from Neanderthals and Denisovans by hundreds of thousands of years, as the Washington Post notes.

The ancient DNA was retrieved from a thigh bone in Spain’s Sima de los Huesos, which translates to “pit of bones,” an archaeological site yielding the largest and oldest collection of human remains ever discovered. Since the late 90’s, the “pit of bones” has allowed scientists to trace mankind’s lineage, and so far, the remains of around 28 skeletons thought to date to around 430,000-years-old have been excavated. A German team’s latest discovery about the Sima people has left the scientific community wondering if it’s time to redraw the human evolution tree.

“It’s fascinating and keeps us all on our toes trying to make sense of it all,” palaeoanthropologist Chris Stringer from the Natural History Museum in London told Nature Magazine. “Instead of just being stuck with trying to resolve the last 100,000 years, we can really start to put some dates from DNA further down the human tree.”

The bones found in Sima de los Huesos were initially attributed to a population that evolved around 100,000 years earlier than the Neanderthals. But a 2013 study found that their DNA is more similar to that of Denisovans (see video, above). So who were these Sima hominins exactly?

To find out, a team at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany analyzed samples taken from a tooth and a thigh bone and concluded that the Sima people were more closely related to ancestors of Neanderthals than those of Denisovans – meaning the two groups must have diverged much earlier than geneticists had suspected – by 430,000 years, according to New Scientist. It also alters the timeline of mankind. If Neanderthals already existed more than 400,000 years ago, researchers suggest that it means the split from our ancestors was as early as 750,000 years ago.

“Starting such a thing is already very ambitious, and managing it is even more impressive,” says Ludovic Orlando, an ancient-DNA researcher at the Natural History Museum of Denmark in Copenhagen. “We are really reaching the limits of what is possible.”

Ewen Callaway from Nature Magazine explains.

“The Sima hominin skulls have the beginnings of a prominent brow ridge, as well as other traits typical of Neanderthals. But other features, and uncertainties around their age – some studies put them at 600,000 years old, others closer to 400,000 – convinced many researchers that they might instead belong to an older species known as Homo heidelbergensis.”

It’s believed that the Homo heidelbergensis did not evolve until 50,000 years after Neanderthal and Denisovans diverged, so many scientists suggest that another obscure species called Homo antecessor – which first appeared more than a million years ago – might also be our common ancestor. Chris Stringer at the Natural History Museum in London says its face is very similar to that of modern humans.

“Research must now refocus on fossils from 400,000 to 800,000 years ago to determine which ones might actually lie on the respective ancestral lineages of Neanderthals, Denisovans and modern humans,” he says.

The oldest human DNA found poses more questions than it answers, and the fact that the Sima de los Huesos fossils revealed that the bones were both genetically Neanderthal and Denisovans, could “represent evidence of an unknown species of human migrating from Africa to Eurasia,” but until more bones are found and analyzed, the speculation continues.

[Image courtesy ShutterStock]