- Homo sapiens and Neanderthals lived alongside each other in the Levant
- The two species existed in an ‘equilibrium’ for tens of thousands of years
- A ‘disease barrier’ kept Homo sapiens from Neanderthal territory
Neanderthals and homo sapiens co-existed for tens of thousands of years in the Levant but a breakdown in an invisible disease barrier may have led to modern humans overwhelming the Neanderthals and then spreading out
The Levant includes a number of modern countries including Cyprus, Israel, Jordan, Syria, Egypt and Iraq.
Researchers believe the mutual fear of contracting diseases held by both Neanderthals and Homo sapiens is behind their ability to co-exist for tens of thousands of years
It is believed that their inefficient stone tools (recreation pictured) saw Neanderthals perish 40,000 years ago, while the homo sapien community boomed to become the origin of modern day humans
After the disease barrier no longer affected modern humans they would have been able to overwhelm the Neanderthals with their superior tools and weapons
The Neanderthals were a cousin species of humans but not a direct ancestor – the two species split from a common ancestor – that perished around 50,000 years ago. Pictured is a Neanderthal museum exhibit
Neanderthals may have been wiped out by tropical diseases carried by homo sapiens as they migrated out of Africa more than 130,000 years ago, a new study has revealed.
Archeological evidence suggests that Eurasian Neanderthals first came into contact with our human ancestors in an area known as the Levant in the Eastern Mediterranean.
The two species survived together for tens of thousands of years before the Neanderthals began disappearing and modern humans expanded beyond the Levant.
In a new report, researchers from Stanford University suggests that Homo sapiens and Neanderthals were locked in a ‘disease stalemate’ for tens of thousands of years.
Gilli Greenbaum from the Stanford team said: ‘Our research suggests that diseases may have played a more important role in the extinction of the Neanderthals than previously thought.
‘They may even be the main reason why modern humans are now the only human group left on the planet.’
The team used mathematical models of modern disease transmission to show how the unique diseases held by Neanderthals and modern humans could have created an ‘invisible disease barrier’ between the two species.
This would have discouraged homo sapiens from entering enemy territory for fear of contracting a disease they had no immunity over.
The researchers claim this ‘uneasy equilibrium’ was eventually broken due to interbreeding between the two species.
The hybrid humans born of these unions may have carried immune-related genes from both species, which would have slowly spread through modern human and Neanderthal populations.
As these protective genes spread, the disease burden or consequences of infection within the two groups gradually lifted.
Eventually, a tipping point was reached when modern humans acquired enough immunity that they could venture beyond the Levant and deeper into Neanderthal territory with few health consequences.
At this point, other advantages that modern humans may have had over Neanderthals — such as deadlier weapons or more sophisticated social structures — could have taken on greater importance.
The reason modern humans replaced Neanderthals and not the other way around, is to do with the severity of the diseases that both species carries, according to the researchers.
‘The hypothesis is that the disease burden of the tropics was larger than the disease burden in temperate regions,’ said study co-author Noah Rosenberg.
‘An asymmetry of disease burden in the contact zone might have favoured modern humans, who arrived there from the tropics.’
He said the modelling found that even small differences in disease burden between the two groups at the outset would have grown over time, eventually giving homo sapiens the edge.
Dr Greenbaum said: ‘It could be that by the time modern humans were almost entirely released from the added burden of Neanderthal diseases, Neanderthals were still very much vulnerable to modern human diseases.
‘Moreover, as modern humans expanded deeper into Eurasia, they would have encountered Neanderthal populations that did not receive any protective immune genes via hybridization.’
The way the Neanderthals succumbed to homo sapiens is similar to what happened when Europeans arrived in the Americas in the 15th and 16th centuries and decimated indigenous populations with their more potent diseases.
If this new theory about the Neanderthals’ demise is correct, then supporting evidence might be found in the archaeological record.
‘We predict, for example, that Neanderthal and modern human population densities in the Levant during the time period when they coexisted will be lower relative to what they were before and relative to other regions,’ Greenbaum said.
The full findings of the study were published in the journal Nature Communications.
The Neanderthals were a close human ancestor that mysteriously died out around 50,000 years ago.
The species lived in Africa with early humans for hundreds of millennia before moving across to Europe around 500,000 years ago.
They were later joined by humans taking the same journey some time in the past 100,000 years.
These were the original ‘cavemen’, historically thought to be dim-witted and brutish compared to modern humans.
In recent years though, and especially over the last decade, it has become increasingly apparent we’ve been selling Neanderthals short.
A growing body of evidence points to a more sophisticated and multi-talented kind of ‘caveman’ than anyone thought possible.
It now seems likely that Neanderthals buried their dead with the concept of an afterlife in mind.
Additionally, their diets and behaviour were surprisingly flexible.
They used body art such as pigments and beads, and they were the very first artists, with Neanderthal cave art (and symbolism) in Spain apparently predating the earliest modern human art by some 20,000 years.