Researchers have begun to unpick how the remnants of Neanderthal DNA resulting from ancient interbreeding might impact the physical and psychiatric health of modern humans. Analyzing 28,000 medical records combined with patients’ genetic data, the researchers found that segments of Neanderthal DNA were associated with effects on the skin, immune system, depression, addiction and metabolism. The research is published in Science.
Dr. Sarah Tishkoff, David and Lyn Silfen University Professor in Genetics and Biology, University of Pennsylvania (webpage):
Expertise: Modern human evolutionary history and the genetic architecture of traits related to adaptation and disease risk in Africa.
“Integrating the Neanderthal dataset with a large and informative human disease dataset based on health records is a novel approach. We should start looking at the question of how inherited Neanderthal variants might impact modern humans, and it’s intriguing that there are trends towards association of Neanderthal variants with things like psychiatric disorders and genes that regulate circadian rhythms.
“But one has to be cautious when looking at the statistical variance associated with complex traits like depression or obesity. It will take a lot of data to establish genetic associations with certainty.
“Let’s say we’re not looking at Neanderthals, but instead at modern human genomes, and we’re trying to find which variants are associated with complex traits. Data from hundreds of thousands of people has only yielded a handful of known genetic variants that play a role in complex traits, and many of these variants are only associated, rather than being known to play a functional role. It will be interesting to see if the suggestive statistical associations with Neanderthal variants identified in this study will be verified as disease causing genetic variants.”
Dr. Rasmus Nielsen, Professor, Department of Integrative Biology, University of California, Berkeley (webpage):
Expertise: Statistical and computational aspects of evolutionary theory and genetics; applications in population genetics and medical statistical genetics.
“I think this study is careful and convincing, and perhaps not surprising. We know that about 2-3% of DNA in humans outside Africa is Neanderthal in origin. What this study shows is that for different phenotypes (the physical result of genes interacting with the environment) a similar percentage of the genetic variance underlying phenotypes is explained by Neanderthal DNA. If 2-3% of your DNA is from Neanderthals, 2-3% of the genetic variation explaining your phenotypes you would also expect to come from Neanderthals. So this study is not particularly surprising. It would be very odd if we had all this Neanderthal DNA and it didn’t, on average, have some effect on observable traits.
“The effect they report is a very small proportion of the genetic variance. It’s a few percent in a huge sample size of 28,000 people. Because we’re talking about genetic variation here the effect is not in one direction – so the study doesn’t show that you’re more (or less) likely to become ill because of Neanderthal DNA.
“The more interesting and surprising conclusion in the paper is that more of the variance in neurological and psychiatric traits are explained by Neanderthal DNA. That is interesting because it suggests that there were more differences in those traits between humans and Neanderthals than in other traits, suggesting perhaps that we are somewhat cognitively differentiated from Neanderthals.”
Dr. Sriram Sankararaman, Assistant Professor, Department of Computer Science & Department of Human Genetics, University of California, Los Angeles (webpage):
Expertise: Statistical genetics; methods to make inferences about recent and ancient admixture.
“We know based on several studies that non-African humans today have 2-3% of their genome that come from Neanderthal populations. After that discovery one of the questions was: does this Neanderthal DNA have any functional impact on modern humans? Previously, most studies looked at this question in one of two ways: either by looking at positions in the genome that we think are functionally important and trying to identify whether Neanderthal DNA makes any substantial contribution; or by looking at how segments of Neanderthal DNA are distributed along the genome, and whether that implies anything about their function.
“What was missing from previous efforts was a way of tying the genetic information about Neanderthal DNA to specific phenotypes, i.e. having certain physical or psychiatric traits. This study uses a large dataset with both genetic information and a variety of phenotypes. So if the authors could identify a specific Neanderthal genetic variant in, say, 10% of the people, then they could ask: do the 10% who carry this allele have a phenotype that looks significantly different from the rest?
“The authors were able to find Neanderthal segments in the genomes and associate them to specific phenotypes. They were also able to say that there are phenotypes, such as being at risk of depression or skin lesions, where the variation in the data has a contribution from Neanderthal DNA. Generally, the effect of these Neanderthals alleles seems small. For things like skin lesions or depression, the percentage of the variance explained by the Neanderthal alleles was of the order of a couple of percent.
“It would be incorrect to conclude from this study that Neanderthal DNA alone is behind risk of depression, or any of the other traits looked at in the study. Many of the traits which the authors looked at are complex so they are influenced by lots of different genes, each of which has a fairly small effect individually.”
Declared interests (see GENeS register of interests policy):
Dr. Sriram Sankararaman: “I work on closely-related topics including archaic introgression and its phenotypic effects.”
No further interests declared
‘The phenotypic legacy of admixture between modern humans and Neandertals‘ by Simonti et al, published in Science on Thursday 11 February, 2015.