New research suggests that Neanderthal interbreeding could be the reason why modern humans are more susceptible to certain health issues, or developing certain traits or characteristics.
A study from the Max Planck Institute of Evolutionary Anthropology published Thursday in the journal Science suggests that for most people, about 1.8 to 2.6 percent of modern human DNA was inherited from our Neanderthal ancestors, with the percentage especially high among people of East Asian descent, and lower in those of western Eurasian descent. This was based on in-depth DNA sequencing conducted on a Neanderthal woman who existed about 52,000 years ago in the caves of Vindija, Croatia.
According to the Los Angeles Times, this marked the second time that scientists were able to conduct genetic reconstruction so detailed that comparisons to modern humans were possible. The first analysis, which was based on an individual who existed about 122,000 years ago in the Siberian province of Altai, suggested that Neanderthal genes took up a 1.5 to 2.1 percent share of modern human genes.
Not only does the new study hint at Neanderthal interbreeding having a greater impact on modern human DNA than once thought, it also suggests that this impact could have influenced disease risk in today's people. According to the researchers, these diseases include those related to "neurological, psychiatric, immunological, and dermatological" traits.
The study suggests that the small percentage of Neanderthal genes in our DNA could have an impact on the buildup of "bad" LDL cholesterol and belly fat, which might mean a greater risk of heart attacks. Rheumatoid arthritis risk was also cited as another possible consequence of Neanderthal-influenced gene variants. On the other hand, the study also revealed that Neanderthal interbreeding also helped early Homo sapiens populations develop greater immunity as they migrated out of Africa.
As the human body creates bone-strengthening vitamin D when the skin is exposed to sunlight, the newly-discovered Neanderthal genes were linked to higher levels of the vitamin. When our human ancestors made the move out of Africa to Eurasia, this could have resulted in a loss of vitamin D, which suggests interbreeding with Neanderthals helped make up for this loss over time.Separately, the Telegraph cited a study that compared ancient DNA to that of 112,000 modern-day British people and revealed that our Neanderthal genes may influence other traits, such as a person's hair color, mood, or their chances of taking up smoking or developing an eating disorder. This ties in to Neanderthal interbreeding because Neanderthals had already lived in Eurasia for thousands of years when early Homo sapiens arrived from Africa, thus making them better adapted to more variable sunlight levels than the new arrivals.
"Skin and hair color, circadian rhythms and mood are all influenced by light exposure," said researcher Dr. Janet Kelso, also from the Max Planck Institute of Evolutionary Anthropology.
"Sun exposure may have shaped Neanderthal phenotypes and that gene flow into modern humans continues to contribute to variation in these traits today."Lawrence Berkeley National Laboratory geneticist Dr. Edward M. Rubin, who was not involved with either study, told the Los Angeles Times that the study of ancient DNA "really is a time machine." He added that the decision of the first study's authors to share their genetic sequencing data to the public "has opened a very rich window" that could allow people to learn more about our Neanderthal ancestors, and how interbreeding resulted in a lot of the characteristics we have today.
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