Fri. Dec 13th, 2019

The Neanderthals would have disappeared because of human diseases


Neanderthals Y Homo Sapiens they shared the area of I raised Mediterranean for tens of thousands of years. Both groups occupied the large area of Middle East located south of the Taurus Mountains, bounded by the sea to the west, the Arabian desert to the south and Mesopotamia to the east. There they lived and even mixed before modern humans expanded into Eurasia.

Archaeological evidence indicates that the initial encounter between Eurasian Neanderthals and our ancestors occurred more than 130,000 years ago. Our distant cousins, however, did not disappear until about 40,000 ago and they did so abruptly. Researchers of the Stanford University They believe they already know why.






Contact

The initial encounter between the Eurasian Neanderthals and our ancestors occurred over 130,000 years ago

As revealed in a study published in the magazine Nature Communications
, the transmission patterns of diseases It would explain that Homo Sapiens would take tens of thousands of years to replace Neanderthals throughout Europe and Asia.

“Our findings suggest that diseases may have played a more important role in the extinction of Neanderthals than previously thought. They may even be the main reason why modern humans are now the only human group left on the planet, ”says Gili Greenbaum, lead author of the analysis, in a statement.


Disappearance

Our distant cousins, however, did not disappear until about 40,000 ago and did so abruptly

Researchers have employed a series of mathematical models to study the behavior of conditions and gene flow. His conclusion is that the unique diseases that harbored Neanderthals and modern humans could have created an invisible barrier to those diseases that discouraged incursions into enemy territory.

Within this narrow area of ​​contact that was the Levant, both groups coexisted in an "uncomfortable balance" that lasted tens of millennia. "That the front of interaction has been limited to the Levant for tens of thousands of years is disconcerting, especially in the light of the short time, a few millennia, in which the replacement was completed in the rest of Eurasia," they point out.





The unique diseases of modern humans and Neanderthals would have created a barrier that hybrids could have broken

The unique diseases of modern humans and Neanderthals would have created a barrier that hybrids could have broken
(Stanford University)




Stanford experts believe that the fact that it could have broken the stagnation and finally allowed our ancestors to supplant the Neanderthals was the union of the two species through miscegenation. "Hybrid humans born from these junctions may have carried genes related to the immune system of both species, which would have spread slowly through modern populations of both humans and Neanderthals," the authors of this study write.

As these protective genes spread, the burden of disease or the consequences of infections within the two groups would have gradually increased. The turning point would have been reached when Homo Sapiens acquired enough immunity to be able to venture beyond the Levant and deepen the Neanderthal territory with few consequences for their health.


Mix between species

Hybrid humans would carry genes related to the immune system of both species






Other advantages that, according to the researchers, modern humans could have had, such as developing more deadly weapons or more sophisticated social structures, would have gained greater importance. "Once a certain threshold is crossed, the disease burden no longer plays a role, and other factors can take action," Greenbaum considers.

To understand why modern humans replaced Neanderthals and not vice versa, biologists modeled what would happen if the set of tropical diseases that our ancestors harbored were more deadly or more numerous than those carried by our distant cousins.


Indigenous populations

The scenario is similar to what happened with the arrival of Europeans to America in the fifteenth and sixteenth centuries

“The hypothesis is that the burden of diseases in the tropics was greater than the burden of diseases in temperate regions. An asymmetry in the contact area could have favored modern humans, who came there from the tropics, ”adds Noah Rosenberg, a professor of genetics and society at Stanford University.

“It could be – the researchers add – that when modern humans were almost completely freed from the additional burden of Neanderthal diseases, they were still very vulnerable to human diseases. Also, as the sapiens expanded rapidly through Eurasia, they would run into Neanderthals no protective genes acquired with hybridization. ”





The scenario proposed by these specialists is similar to what happened when Europeans arrived in the Americas in the fifteenth and sixteenth centuries and decimated indigenous populations with their most potent diseases. His goal now is to be able to corroborate his hypothesis with the archaeological record.







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