23 Apr 2019

The evolutionary purpose of depression and anxiety

From Afternoons with Jesse Mulligan, 3:08 pm on 23 April 2019

Evolution explains so much about our bodies, and it may be able to explain a lot about our minds, according Dr Randolph Nesse.

We live in an age of anxiety with rates of depression skyrocketing all over the world. But there may be an evolutionary purpose for all this suffering says Dr Randolph Nesse. It's an idea based on his years of work in the areas of psychiatry and evolution.  He says natural selection would have gotten rid of autism, schizophrenia, and manic-depressive illness, so they are written in our genes for a reason.

He explores the possibilities in his new book, Good Reasons for Bad Feelings: Insights from the Frontier of Evolutionary Psychiatry

Sad woman hugging her husband

Photo: 123RF

Evolutionary psychiatry is a subset of a larger growing field called evolutionary medicine, which has been explored for 25 years.

“We all got started by asking a question about disease. Instead of asking why this person gets sick, we decided to ask why are all of us so vulnerable to so many disorders – it almost seems like somebody goofed in the design phase here.”

Some mental illnesses are exaggerations of useful responses, he says.

“If you go to the doctor with pain, or fever or nausea or cough, those are symptoms not diseases. You expect your doctor to figure out what’s causing it. If you go into your psychotherapist or psychiatrist with anxiety or anger or jealousy and you say ‘hey, these are terribly unpleasant feelings’ nowadays what you usually get is ‘yep, there’s probably something wrong with it you and especially your brain, let’s try to figure out what’s wrong with you.”

Evolution takes a step back and these are put in a medical context.

He’s asking why we have these emotions in the first place and why did natural selection set them off at certain times, in certain situations.

“It doesn’t mean they are useful every single time, but they are there for good reasons.”

An example of it not always being useful is people who are born without any capacity for pain – it’s sounds great until you look at them and realise they almost all die early, he says.

 “All kinds of medical symptoms are really unpleasant, nobody likes to have a cough or diarrhoea or vomiting and it probably is a good thing that those things are present, that keeps us from getting back into the same situation again that cause something bad to happen.

“Likewise, if you just about got bit by a lion, you should be very careful about going back to that place again and that uncomfortable feeling of anxiety really motivates you strongly to stay away from that spot, or at least you’ll be really, really careful.”

Most people have way more anxiety than we need, he says. This is because if you think there might be a lion behind the rock, even a slight chance, you should run.

Low mood, he says, is a mild depression that shows up for good reasons. Some depression is plain old depression, a bit like a chronic pain, it’s an abnormality in the system.

“If you say depression, everybody assumes it’s a disease and abnormal…”

He says we think there must be something different in the brains of people who have these disorders.

“We’ve been looking for about 20 years now for different genetic variations and it turns out not only have we not found them, there are no genetic variations of common genes that influence the risks of these common disorders by more than a percent or two.”

While there are some distinctive brain differences in people with schizophrenia, autism and even depression, they aren’t different enough to make a diagnosis, he says.

“One way to go forward is to use the same evolutionary principles that underlie the study of all animal behaviour and really that underlie the rest of medicine too. The rest of medicine distinguishes very distinctly between symptoms like cough, fever and nausea, and diseases like cancer and infection and all the rest.”

This can put psychiatry on the same foundation as the rest of medicine, he says.

For people wondering why natural selection doesn’t just get rid of things like schizophrenia, Dr Nesse has an idea.

“I ask myself, why is it that race horses break their leg so often? For every 1000 race horse starts, a race horse breaks its leg. It turns out it’s because race horses are bred for speed and every generation the leg bones get longer and thinning and lighter and more prone to break. They get pushed right up to the edge where they’re as fast as possible at the cost of being vulnerable to breaking.

“Our minds have also been shaped very fast, to run fast an efficiently and creatively and do all the marvellous things that human minds can do. Talking with each other is just a miracle that other species can’t do and thinking and logic and all the rest.”

There might, however, be a price for this, says Dr Nesse. Natural selection has pushed this to a cliff edge.

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