A 124,000-year-old femur discovered in a cave in southwestern Germany is the latest piece of evidence that could help scientists understand more about the complicated relationship between modern humans and Neanderthals. Or so they hope.
Over the last three centuries, scientists have been trying to pinpoint the exact timeline of the origin of modern humans (Homo sapiens).
The general consensus appears to be that Homo sapiens evolved sometime between 300,000 to 400,000 years ago in Africa and moved to other continents around 70,000 years ago – laying the foundation of the populations of people today.
But things get trickier. Scientists have been finding small bits of evidence that contradicts the expert consensus and this ancient leg bone adds yet another twist to the story.
Both Neanderthals and living humans are thought to have evolved from a common ancestor.
The Neanderthals are considered either a distinct species, Homo neanderthalensis, or more rarely, as a subspecies of Homo sapiens. They are also related to another extinct human relatives called the Denisovans.
Researchers from the Max Planck Institute for the Science of Human History and the University of Tubingen, both in Germany, found traces of mitochondrial DNA in the Neanderthal bone that is similar to mitochondrial DNA in modern humans.
And given that the bone has been dated at roughly 124,000 years old, it means dispersal of the modern humans to Europe may be much earlier than thought – sometime between 470,000 and 220,000 years ago.
“The bone, which shows evidence of being gnawed on by a large carnivore, provided mitochondrial genetic data that showed it belongs to the Neanderthal branch,” says lead researcher Cosimo Posth of the Max Planck Institute.
So what does it mean?
The researchers have a theory: a small group of early Homo sapiens, or maybe close relatives of our species, made their way from Africa to Europe and interbred with Neanderthals.
The ancient African migrants later disappeared but some of their DNA remained in later generations of Neanderthals.
This explanation also offers another problem scientists have been trying to solve for years – why previous research analysing nuclear DNA shows humans and Neanderthals split 765,000 to 550,000 years ago while mitochondrial DNA analysis puts the split at 365,000 years later?
But if a small team of human ancestors made its way into Europe and interbred with the Neanderthals, that discrepancy might make sense.
“This scenario reconciles the discrepancy in the nuclear DNA and mitochondrial DNA phylogenies of archaic hominins and the inconsistency of the modern human-Neanderthal population split time estimated from nuclear DNA and mitochondrial DNA,” said Johannes Krause, also of the Max Planck Institute and senior author of the study.
However, researchers admit there isn’t enough evidence to support this theory and say they need nuclear DNA from the femur bone to paint a better picture of the Neanderthal it belonged to.
Until then, the story of our origin and the relationship our ancestors may have had with Neanderthals will continue to remain a mystery.
This research is published in the journal Nature Communications.
