Neanderthals may have been infected by diseases carried out of Africa by humans

April 10, 2016
Dr. Simon Underdown (with skull), Cambridge alumnus, is now Principal Lecturer in Biological Anthropology at Oxford Brookes. Credit: Simon Underdown

A new study suggests that Neanderthals across Europe may well have been infected with diseases carried out of Africa by waves of anatomically modern humans, or Homo sapiens. As both were species of hominin, it would have been easier for pathogens to jump populations, say researchers. This might have contributed to the demise of Neanderthals.

Researchers from the universities of Cambridge and Oxford Brookes have reviewed the latest evidence gleaned from pathogen genomes and DNA from ancient bones, and concluded that some infectious diseases are likely to be many thousands of years older than previously believed.

There is evidence that our ancestors interbred with Neanderthals and exchanged genes associated with . There is also evidence that viruses moved into humans from other hominins while still in Africa. So, the researchers argue, it makes sense to assume that humans could, in turn, pass disease to Neanderthals, and that - if we were mating with them - we probably did.

Dr Charlotte Houldcroft, from Cambridge's Division of Biological Anthropology, says that many of the infections likely to have passed from humans to Neanderthals - such as tapeworm, tuberculosis, and types of herpes - are chronic diseases that would have weakened the hunter-gathering Neanderthals, making them less fit and able to find food, which could have catalysed extinction of the species.

"Humans migrating out of Africa would have been a significant reservoir of tropical diseases," says Houldcroft. "For the Neanderthal population of Eurasia, adapted to that geographical infectious disease environment, exposure to new pathogens carried out of Africa may have been catastrophic."

Dr Charlotte Houldcroft is in the laboratory at Biological Anthropology in Cambridge. Credit: Charlotte Houldcroft

"However, it is unlikely to have been similar to Columbus bringing disease into America and decimating native populations. It's more likely that small bands of Neanderthals each had their own infection disasters, weakening the group and tipping the balance against survival," says Houldcroft.

New techniques developed in the last few years mean researchers can now peer into the distant past of modern disease by unravelling its genetic code, as well as extracting DNA from fossils of some of our earliest ancestors to detect traces of disease.

In a paper published today in the American Journal of Physical Anthropology, Houldcroft, who also studies modern infections at Great Ormond Street Hospital, and Dr Simon Underdown, a researcher in evolution from Oxford Brookes University, write that genetic data shows many have been "co-evolving with humans and our ancestors for tens of thousands to millions of years".

The longstanding view of infectious disease is that it exploded with the dawning of agriculture some 8,000 years ago, as increasingly dense and sedentary human populations coexisted with livestock, creating a perfect storm for disease to spread. The researchers say the latest evidence suggests disease had a much longer "burn in period" that pre-dates agriculture.

In fact, they say that many diseases traditionally thought to be 'zoonoses', transferred from herd animals into humans, such as tuberculosis, were actually transmitted into the livestock by humans in the first place.

"We are beginning to see evidence that environmental bacteria were the likely ancestors of many pathogens that caused disease during the advent of agriculture, and that they initially passed from humans into their animals," says Houldcroft.

"Hunter-gatherers lived in small foraging groups. Neanderthals lived in groups of between 15-30 members, for example. So disease would have broken out sporadically, but have been unable to spread very far. Once agriculture came along, these diseases had the perfect conditions to explode, but they were already around."

There is as yet no hard evidence of infectious disease transmission between humans and Neanderthals; however, considering the overlap in time and geography, and not least the evidence of interbreeding, Houldcroft and Underdown say that it must have occurred.

Neanderthals would have adapted to the diseases of their European environment. There is evidence that humans benefited from receiving genetic components through interbreeding that protected them from some of these: types of bacterial sepsis - blood poisoning occurring from infected wounds - and encephalitis caught from ticks that inhabit Siberian forests.

In turn, the humans, unlike Neanderthals, would have been adapted to African diseases, which they would have brought with them during waves of expansion into Europe and Asia.

The researchers describe Helicobacter pylori, a bacterium that causes stomach ulcers, as a prime candidate for a disease that humans may have passed to Neanderthals. It is estimated to have first infected humans in Africa 88 to 116 thousand years ago, and arrived in Europe after 52,000 years ago. The most recent evidence suggests Neanderthals died out around 40,000 years ago.

Another candidate is herpes simplex 2, the virus which causes genital herpes. There is evidence preserved in the genome of this disease that suggests it was transmitted to humans in Africa 1.6 million years ago from another, currently unknown hominin species that in turn acquired it from chimpanzees.

"The 'intermediate' hominin that bridged the virus between chimps and humans shows that diseases could leap between hominin species. The herpesvirus is transmitted sexually and through saliva. As we now know that humans bred with Neanderthals, and we all carry 2-5% of Neanderthal DNA as a result, it makes sense to assume that, along with bodily fluids, humans and Neanderthals transferred diseases," says Houldcroft.

Recent theories for the cause of Neanderthal extinction range from climate change to an early human alliance with wolves resulting in domination of the food chain. "It is probable that a combination of factors caused the demise of Neanderthals," says Houldcroft, "and the evidence is building that spread of disease was an important one."

Explore further: Model suggests Neanderthal extinction occurred due to human cultural superiority

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NoStrings
4.5 / 5 (4) Apr 10, 2016
Brilliant. Someone finally thought about it. That is how we pretty much depopulated South America, Australia, etc., and we were separated from these populations only 15-30 Ky, and were already very deadly to them. Now think 200 Ky, how toxic we can become to people in a pretty isolated environment in this time span.

This theory makes so much sense, as opposed to our default self-deluded ponderings about our 'cultural superiority' , a representative article published just a couple of months back: http://phys.org/n...tml#nRlv
Thorium Boy
1.7 / 5 (12) Apr 11, 2016
Anthropologists are left-wingers who hate humans, especially white humans. They have a knack for contriving scenarios where man is evil. More than a few of these crackpots have advocated the depopulation of Earth of humans.
AGreatWhopper
1 / 5 (5) Apr 11, 2016
Vermin is as vermin does. Crackpot.
Squirrel
5 / 5 (3) Apr 11, 2016
Well known process. Two species cross infect each other causing one to go extinct. All it requires is that one is better adapted to the infection. Indeed, an infection might be selected to cause less morbidity and mortality in one species if it advantages the survival of that species by helping eliminate by cross infection to another one with which it competes. This could have occurred not only between anatomically modern humans and Neanderthals but earlier between Homo and Australopithecus species: Homo picking up zoonoses infections from scavenging on the Savannah that then cross infected its closely related Australopiths. Chimpanzees and Gorillas survived due to being less closely related and living in a different niche that helped isolated them from such infections.
Squirrel
5 / 5 (2) Apr 11, 2016
Houldcroft's paper "Neanderthal genomics suggests a pleistocene time frame for the first epidemiologic transition" can be found here (paywall) http://onlinelibr...abstract
Squirrel
5 / 5 (4) Apr 11, 2016
An open access source for the paper can be found on the biorxiv server http://biorxiv.or...1/017343 http://dx.doi.org...1/017343
torbjorn_b_g_larsson
5 / 5 (1) Apr 11, 2016
As always, paleoanthropologist John Hawks gives a context:

"when it comes to understanding Neandertal and modern human interactions, we have had lots and lots and lots of models and few testable predictions."

"If we assume that "culture level" was a continuous variable, and that "modern humans" had a higher rate of increase than Neandertals, we get a very simple pattern. The data are not a simple pattern. So the "culture level" model seems like a bad model to account for the complexity of what actually happened."

"this means it was not just "culture level" that made a difference. I can imagine that there may have been some specific aspects of culture, which may not have been archaeologically visible, that made a key difference. "

[tbctd]
torbjorn_b_g_larsson
5 / 5 (1) Apr 11, 2016
[ctd]

"this means it was not just "culture level" that made a difference. I can imagine that there may have been some specific aspects of culture, which may not have been archaeologically visible, that made a key difference. "

"I can also imagine that non-cultural factors were more important. For example, disease has been a key factor underlying the survival or replacement of populations during the past 10,000 years. It is not a stretch to imagine that disease influenced the Neandertals and other archaic peoples differently from each other and from modern humans. The evidence for selection on genes related to immunity from these archaic humans is now strong, and some of these may reflect pathogens or parasites that were important at the time of population contacts among these people."

[ http://johnhawks....016.html ]

[tbctd]
torbjorn_b_g_larsson
4 / 5 (2) Apr 11, 2016
[ctd]

So yes, culture level models are (should be) considered off the table, and diseases a very likely suspect, for differences in population sizes.

But note that there is very little science (testable models) in this area so far.
metingunduz
not rated yet Apr 12, 2016
Excellent and most logical suggestion of the `extinction theory of Neanderthals as well as Denisovans ` INFECTIOUS DISEASES and GENETIC PREDISPOSITION DIFFERENCES IN BETWEEN POPULATIONS IN DIFFERENT GEOGRAPHIES AND EVENTUAL INTERACTION BY MIGRATION AND CLOSE INTERACTION AS WELL AS INTERBREEDING IN BETWEEN THEM RESULTS IN `THE SURVIVAL OF THE FITTEST -THE ONE WHICH IS ARMED WITH NATURAL RESISTANCE TO THE INFECTIOUS AGENTS (VIRUS-BACTERIA- CHLAMYDIA AS WELL AS PARASITIC AGENTS) WHICH IS CARRIED BY` PORTER` MEMBERS OF EACH SOCIETY IN ANY POPULATION ... WHAT DETERMINES WHO LIVES AND WHO PERISHES IS THE ACQUIRED AND NATURAL IMMUNITY AS WELL AS THE VIRULENCE OF THE INFECTIOUS AGENTS CARRIED BY THE `PORTER` MEMBERS OF THE SPECIES .
DavidH
5 / 5 (3) Apr 12, 2016
I find something very disturbing in the way this article frequently seems to distinguish between "Humans" and "Neanderthals". Neanderthals were also humans. Sapiens are simply the only surviving humans.
Rute
5 / 5 (2) Apr 12, 2016
Ever since I read about the devastation that diseases carried by Europeans caused in Americas, I thought a similar chain of events might explain partly the disappearance of the Neanderthals as well. I'm glad scientists have researched into this topic.

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