Diseases brought by modern humans from Africa, could have helped drive European neanderthals to extinction, according to a new study.
Writing in the American Journal of Physical Anthropology, researchers from Cambridge and Oxford Brookes say since both species are hominins, “it would have been easier for pathogens to jump populations.”
The researchers reached their conclusions based on the study of pathogen genomes and ancient bones, which they say reveal that “some infectious diseases are likely to be many thousands of years older than previously believed.”
"Humans migrating out of Africa would have been a significant reservoir of tropical diseases,"said Charlotte Houldcroft, from Cambridge's Division of Biological Anthropology.
"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.
"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," she added.
Some of the possible diseases include “tapeworm, tuberculosis, stomach ulcers and types of herpes,” researchers said. Catching these chronic conditions could have weakened Neanderthals, making it harder for them to forage and hunt.
There have been several studies suggesting homo sapiens interbred with Neanderthals, which could have allowed the exchange of disease causing pathogens.
The conventional wisdom about infectious diseases is that they “exploded” as humans started agriculture, where humans were in closer contact and lived near livestock.
"Hunter-gatherers lived in small foraging groups. Neanderthals lived in groups of between 15-30 members, for example,” said Houldcroft.
“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."
The researchers added that Neanderthals would have developed resistance to native diseases, while homo sapiens would have developed resistance to African diseases.
One example the researchers give is Helicobacter pylori, which causes stomach ulcers. They say the disease first infected African humans 88- to 116- thousand years ago. It arrived in Europe around 52,000 years ago.
Neanderthals are believed to have gone extinct around 40,000 years ago.
Another might be herpes simplex 2, which causes genital herpes. There is evidence it was passed to African humans 1.6 million years ago from chimpanzees.
"The 'intermediate' hominin that bridged the virus between chimps and humans shows that diseases could leap between hominin species. The herpes virus is transmitted sexually and through saliva. As we now know that humans bred with Neanderthals, and we all carry two to five percent of Neanderthal DNA as a result, it makes sense to assume that, along with bodily fluids, humans and Neanderthals transferred diseases," said Houldcroft.
There are several theories about what happened to Neanderthals, including climate change, but researchers think it was likely a combination of factors.