Saturday, 13 February 2016

Neanderthal ancestry and depression risk - why nothing in medicine makes sense except in the light of evolution

Evolutionary biology, as I have pointed out repeatedly is of practical utility for medicine in areas ranging from the classics such as rational antibiotic prescription, tumour biology, and epidemiology, through to understanding the many design flaws and quirks in our anatomy and genetics which make sense only when seen as a result of our evolutionary origins. These facts readily explain both the trend towards making evolutionary biology a basic clinical science for medical students, and the growth in the new field of evolutionary medicine.

They also go a long way to pointing out why intellectually honest, informed doctors are incredulous when people tell them that evolution is 'science falsely so-called'. It's impossible to deny evolution when you can see bacteria evolving drug resistance, have a knowledge of the multiple design flaws in our anatomy that can be explained only by evolution, know from clinical genetics that many genes have coalescent times stretching back hundreds of thousands of years, or are aware of the multiple retrotransposon fragments in identical places in human and ape genomes.  In fact, we've moved beyond the novelty of seeing the indelible hand of evolution anywhere from gross anatomy down to the genomic, and are now building on the fact of evolution to see whether Neanderthal ancestry is linked with the risk of disease. It's not only game, set and match for evolution. We've moved onto the next round of the competition.

One of the more fascinating developments of genomics has been the revelation that non-African humans have varying degrees of Neanderthal ancestry. This of course is further evidence falsifying the special creationist belief that every single human being alive descends exclusively from two people who lived 6000 years ago, though that argument had been falsified years before the Neanderthal genome was sequenced and compared with ours. However, as I noted, we've long moved beyond the novelty of recognising that our ancestry stretches back into the remote past and that some of us have ancestry from at least two species of humans, and are now looking at the real-world clinical applications of this.

A recent paper in Science [1] emphasises this point by raising the question of whether Neanderthal ancestry has had any effect on our susceptibility to disease. The authors looked at both medical records and genetic data, and found an association between Neanderthal genes and dermatological,  haematological, and psychiatric disorders. This does not mean that your Neanderthal ancestry directly increases your risk of getting depression. As the study leader Tony Capra points out, "[i]t seems Neanderthal DNA has an effect on systems that regulate our moods or behaviors,” says Capra, “but for now, I don’t feel comfortable saying more than that.” [2]

Science journalist Ed Yong also quotes the palaeoanthropologist and geneticist John Hawks who not only reiterates the point that Neanderthal genes do not predestine one to disease, but do have detectable influences which can be of clinical significance:
“The Neanderthal genes are not disease agents,” says John Hawks from the University of Wisconsin-Madison, who was not involved in the study. But they’re “there in the brain, doing things, and having some detectable effects on behavioral outcomes. That’s amazing.” He and Capra both note that working out the role of these genes might help us to understand the underlying biology behind depression and other disorders.  [3]
That is the point Capra's team make in the closing paragraph of their article:
EHR data, paired with DNA sequencing, hold promise for characterizing the phenotypic impact of regions identified through evolutionary analyses. However, there are currently limitations to this approach. It is difficult to extract nonclinical phenotypes from EHRs, and we were not able to analyze all Neandertal haplotypes due to the limited coverage of the available genotyping data. Nonetheless, as EHRs are increasingly linked to whole-genome sequence data and more sophisticated methods are developed for extracting phenotypes from the rich data stored in EHRs, we anticipate further insights into the functional effects of archaic introgression. [4] (Emphasis mine)
What this shows is that we are now moving from the novelty of realising that non-Africans have Neanderthal ancestry, and looking at the clinical implications of this fact. Once again, this is why anyone who claims that evolution is false simply has no idea what they are talking about. Nothing in medicine makes sense except in the light of evolution.


1. Simonti C.N. et al "The phenotypic legacy of admixture between modern humans and Neandertals" Science (2016) 351:737-741 DOI: 10.1126/science.aad2149
2. Yong E "The Link Between Neanderthal DNA and Depression Risk" The Atlantic Feb 11 2016
3. ibid
4. Simonti C.N., p 741