A new study published in the American Journal of Physical Anthropology suggests that the transfer of infectious pathogens between populations of Neanderthals and anatomically modern Homo sapiens may have played a role in the extinction of Neanderthals.
Neanderthals. Image credit: University of Utah via kued.org.
Recent hypotheses 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. And the evidence is building that spread of disease was an important one,” said study lead author Dr. Charlotte Houldcroft, a researcher with the University of Cambridge and UCL Institute of Child Health.
According to Dr. Houldcroft and co-authors, many of the infections likely to have passed from humans to Neanderthals – such as tapeworm, tuberculosis, stomach ulcers and types of herpes – are chronic diseases that would have weakened the hunter-gathering Neanderthals, making them less fit and able to find food.
“Hunter-gatherers lived in small foraging groups,” Dr. Houldcroft said. “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.”
“By combining skeletal, archaeological and genetic evidence from modern humans and extinct Eurasian hominins (Neanderthals and Denisovans), we question whether the first epidemiologic transition in Eurasia featured a new package of infectious diseases or a change in the impact of existing pathogens,” the scientists said.
“Coupled with pathogen genomics, this approach supports the view that many infectious diseases are pre-Neolithic.”
They describe Helicobacter pylori — a bacterium that causes stomach inflammation (gastritis) and ulcers in the stomach and duodenum — as a prime candidate for a disease that anatomically modern humans may have passed to Neanderthals.
It is estimated to have first infected humans in Africa 88,000 to 116,000 years ago, and arrived in Europe after 52,000 years ago.
Another candidate is the herpes simplex type 2 virus (HSV-2), a genitally transmitted virus that also causes painful sores.
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.
“Humans migrating out of Africa would have been a significant reservoir of tropical diseases,” Dr. Houldcroft said.
“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.”
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Charlotte J. Houldcroft et al. Neanderthal genomics suggests a Pleistocene time frame for the first epidemiologic transition. American Journal of Physical Anthropology, published online April 10, 2016; doi: 10.1002/ajpa.22985
