Summary: Traits with the strongest Neanderthal DNA contribution were sleep patterns, smoking habits, and alcohol consumption.
Source: Estonian Research Council
It has long been known that human brain disorders such as neurological or psychiatric disorders run in families, suggesting some heritability. Consistent with this hypothesis, genetic risk factors for the development of these diseases have been identified.
However, fundamental questions about the evolutionary drivers remained elusive. In other words, why aren’t genetic variants that increase the risk of disease eliminated during evolution?
Answering these questions was notoriously difficult. However, new discoveries about events in the deep human past have given scientists new tools to unravel these mysteries: When modern humans left Africa over 60,000 years ago, they met and mixed with other archaic humans like the Neanderthals.
About 40% of the Neanderthal genome is still found in non-Africans today, and each individual still carries about 2% of Neanderthal DNA. Some of the archaic genetic variants may have provided benefits at some point in our evolutionary past.
Today, scientists can use this information to learn more about the impact of these genetic variants on human behavior and risk of developing disease.
Using this approach, a new study by an international team led by researchers from the University of Tartu, Charité Berlin and UMC Amsterdam analyzed Neanderthal DNA associations with a variety of more than a hundred brain disorders and traits such as sleep, smoking or alcohol use in the British biobank with the aim of constraining the specific contribution of Neanderthal DNA to the variation in behavioral traits in humans today.
The study found that while Neanderthal DNA showed a disproportionate number of associations with multiple traits associated with central nervous system diseases, the diseases themselves did not show significant numbers of Neanderthal DNA associations.
Traits with the strongest Neanderthal DNA contribution included smoking habits, alcohol consumption, and sleeping habits. Using data from other cohorts such as the Estonian Biobank, the Netherlands Study of Depression and Anxiety, FinnGen, Biobank Japan and deCode, some of these results could be replicated.
Particularly noteworthy are two independent Neanderthal variants with a high risk of a positive smoking status, which were found in the UK Biobank and Biobank Japan, respectively.
“Our results suggest that Neanderthals carried several variants that significantly increase the risk of smoking in humans today. What phenotypic effects these variants had in Neanderthals is still unclear.
“However, these results offer interesting candidates for further functional testing and may help us in the future to better understand Neanderthal-specific biology,” said Michael Dannemann, associate professor of evolutionary genomics at the University of Tartu and lead author of this study.
“The significant associations of Neanderthal DNA with alcohol and smoking habits could help us decipher the evolutionary origin of addictive and rewarding behaviors,” added Stefan M. Gold, professor of neuropsychiatry at the Charité in Berlin, who co-led this study .
“It is important to note that sleep problems, alcohol and nicotine use have been consistently identified as common risk factors for a range of neurological and psychiatric disorders. On the other hand, there are some intriguing findings from anthropology that suggest some social benefits of higher tolerance to these substances among hunter-gatherers.
“Hence, our results support the hypothesis that it is not brain diseases themselves that have evolutionary explanations, but that natural selection shapes traits that make us susceptible to them in the modern context.”
“Neanderthals inhabited parts of Eurasia more than 100,000 years before modern humans left Africa to inhabit the rest of the world. The high frequency of some of the variants associated with different sleep patterns could indicate that these were beneficial outside of Africa – an environment defined by different seasonalities and UV light exposure, for example, than the environment of modern humans,” adds Dannemann .
About this news from genetic and evolutionary neuroscience research
Author: Carlos Kuiv
Source: Estonian Research Council
Contact: Carlos Kuiv – Estonian Research Council
Picture: The image is in the public domain
Original research: Open access.
“Neanderthal introgression subdivides the genetic landscape of neuropsychiatric disorders and associated behavioral phenotypes” by Michael Dannemann et al. Translational Psychiatry
Neanderthal introgression subdivides the genetic landscape of neuropsychiatric disorders and associated behavioral phenotypes
Despite advances in identifying the genetic basis of psychiatric and neurological disorders, fundamental questions about their evolutionary origins remain elusive.
Here crossed variants of archaic humans like the Neanderthals can serve as a fascinating research paradigm.
We compared the number of associations for Neanderthal variants with the number of associations for frequency-matched non-archaic variants with respect to human CNS disorders (neurologic and psychiatric), nervous system drug prescriptions (as proxies for disease), and related, non-disease phenotypes in the British Biobank (UKBB).
While no enrichment for Neanderthal genetic variants for psychiatric or neurological disease categories was observed in the UKBB, we found significant associations with certain behavioral phenotypes, including pain, chronotype/sleep, smoking, and alcohol consumption.
In some cases, the enrichment signal was driven by Neanderthal variants, which represented the strongest association genome-wide. SNPs within a Neanderthal haplotype associated with smoking in the UKBB could be replicated in four independent genomic datasets.