There’s an evolutionary basis to mental illness


The human body isn’t very well designed. Our eyes have a blind spot. We have too many bones in our feet and way too many teeth. Our pelvises are too narrow. We have achy backs and knees from walking upright, for goodness sake, and we’ve been doing that for about six million years.

It’s one thing to accept the flawed and fallible nature of the human form. Consider it within the context of evolution, however, and it becomes a bit harder to comprehend. We’re taught evolution as based purely on the survival of the best-adapted traits, where form evolves to perform function, and maybe there isn’t an actual intelligent designer, but there might as well be. Why, then, do our bodies often seem so poorly adapted to the environments we live in? How does evolution explain hiccups and tooth decay and phlegm? How, indeed, does evolution explain mental illness?

Why are our bodies so poorly adapted to the environments we live in?

Introducing antagonistic pleiotropy – the idea that all genes are basically an evolutionary trade-off. Genes are selfish, and they’re selfish because they have to be. Natural selection doesn’t reward genes that offer health or happiness. Natural selection rewards genes that offer reproductive success; in other words, genes that make more genes. The abject misery of depression might not seem a reasonable trade-off for its proposed adaptations, but the genes, well, they disagree.

If you’re interested, it’s thought that some of depression’s adaptations include shutting down behaviours that have more potential risk than return and concentrating attention on analysing complex problems in order to solve them. This, according to evolutionary theory, is why depression makes you withdraw from activities and why you may find yourself ruminating. There are a whole host of other theories to explain other depressive symptoms.

It’s also worth remembering how much the modern world differs from the environment in which many of these genes initially evolved. The first fossils of early humans are estimated to be about 4 million years old. On an evolutionary time scale, that’s about five minutes, and yet it boggles the mind to think of how different the environment of those early humans was.

Natural selection doesn’t reward genes for health or happiness

Isn’t it easy to see how genes that are made to assist a hunter-gatherer would be anxiety-inducing when faced with the concept of the twenty-four-hour cycle? That fairly innocent, reward-seeking genes could make you behave differently when smartphones cruelly deal out dopamine in response to every notification?

It has been hypothesised that the repetitive checking and circular thought associated with Obsessive-Compulsive Disorder might have evolved as a sort of risk-avoidance mechanism. That’s a sensible evolutionary strategy, until it’s faced with social media, which rewards repetitive checking and circular thought. What was originally a feature can easily look like a bug in the context of our nervous planet. Our knees worked better when we walked on four limbs instead of two, and maybe our brains aren’t so different.

(As an aside, remember social media doesn’t want to offer you health or happiness any more than natural selection does. Not unlike the way your genes want to make more genes, social media wants to keep you on social media).

So what? It’s all well and good to know there’s an evolutionary basis for mental illness, but it doesn’t really help someone in the throes of dealing with one. Well, I think there’s a potentially comforting moral to this story.

I know it’s unpopular thinking, trying to draw any kind of positive from mental illness, lest it strays into romanticising. We’re encouraged to think of our mental illnesses as black clouds in the otherwise blue sky of our minds, to struggle against them, to address every negative thought head-on, to take up running, to meditate, anything to fix the problem our minds have created. For many years, my own favourite motif for my depression was my ‘brain goblin’.

My genes aren’t trying to make me miserable, they’re just trying to help me survive

But it’s not a goblin. It’s just my genes. Or not even ‘my’ genes, as such, but just ‘the’ genes; the millennia-old genetic signatures I’m currently providing a home for. They’re not trying to make me miserable. They’re just trying to help me survive, and it’s gone a bit wonky.

Unconventional? Perhaps. But just as it can be comforting to remember our cosmic insignificance (not as distressing as it might seem – see Carl Sagan’s Pale Blue Dot for an example), it can be comforting to remember our biological significance. Trillions of cells, billions of years of evolution, millions of heartbeats, hundreds of thousands of miles of blood vessels. About 20,000 genes, 206 bones, 28 teeth if you’re lucky, and just one you. If you ask me, that’s pretty cool.

Image: ZEISS Microscopy via Flickr

Leave a Reply

Your email address will not be published.


This site uses Akismet to reduce spam. Learn how your comment data is processed.