I was pretty proud of my headline for the the latest research story on the impact of Neanderthal interbreeding with early modern humans: ‘The pros and cons of dating a Neanderthal‘. It raised a smirk among my colleagues, and was actually relevant: two new research papers describe how early humans leaving Africa 60,000 years ago interbred with Neanderthals, receiving genes for better adapted hair and skin, but also the propensity for certain diseases.
The Museum’s human origins expert, Prof Chris Stringer, was quoted in a syndicated story that appeared in quite a few national newspapers. The story itself was relatively ok, but included the slightly complicated fact from the studies that 20% of the Neanderthal genome lives on in modern non-African people. However, each individual person carries no more than about 2% Neanderthal DNA.
The problem is, each newspaper got to choose its own headline to go with the story. And some clearly didn’t read it. At least, they made no attempt to understand it. Case in point: The Mirror, which screamed: ‘Humans are one-fifth Neanderthal, according to shock new scientific study‘.
This shows a fundamental misunderstanding of what the very first few lines of the story actually say:
“The journal Science suggests that up to a fifth of the Neanderthal genome may have survived in modern human populations. This was despite the fact that the proportion of Neanderthal DNA in any one individual is low, around 2% to 4%.”
(Not to mention that ‘the journal Science‘ suggests nothing itself – the authors of the research papers do, not the journal.)
They gave us diseases
Other headlines also contained misunderstandings. The Daily Mail helpfully explained: ‘Are you a hairy diabetic who smokes and suffers from stomach cramps? Your NEANDERTHAL ancestry is to blame‘. What the studies found were Neanderthal genes in spots in the human genome (complete genetic map) that correlate with hair, skin, with diseases like Crohn’s, Type 1 diabetes and lupus, and with ‘smoking behaviour’ and ‘long-term depression’.
The diseases are an interesting story in themselves, and created quite the biology lesson in our office as my boss (and former biological researcher) explained the roots of autoimmune diseases, like Crohn’s and lupus. They appear to arise when our immune systems overreact, and the current thinking goes that this happens when the part of our immune system programmed to fight parasites has nothing left to fight in our modern world, and turns against us. My boss suggested that the genes we got from Neanderthals that cause these diseases today were, at the time, advantageous in helping us fight parasites.
Behaviour on the brain
But, ‘smoking behaviour’ and ‘long-term depression’ are more complex. The smoking part likely has something more to do with the inability to give up smoking; i.e. it is linked with addictive behaviour.
The two studies showed there were large regions of the human genome completely free of Neanderthal DNA, suggesting they were wiped clean by evolution. So why did we keep the genes associated with long-term depression? Again, we waxed lyrical in the office; there must have been some benefit to our ancestors. Perhaps the build-up of stress was necessary for our ancestors, to feed the constant fight-or-flight reflex of survival. Now, like the parasite-fighting immune response, it’s no longer needed, so it overreacts and causes us harm instead.
Aside from the misinterpretations, many of the stories floating around failed to make a distinction between modern African and non-African humans. Sub-Saharan African populations did not inherit these Neanderthal genes: they didn’t leave Africa and didn’t interbreed with Neanderthals. Yet most of the articles refer to ‘us’ and ‘humans’ being 2% Neanderthal and inheriting diseases, completely disregarding the population of ‘us’ that doesn’t contain Neanderthal DNA.