‘Depression is NOT a disorder, it’s an Adaptation Gone Rogue’ says Evolution.
Let’s get straight to the point. A psychiatrist told me not to break my head in understanding what causes depression. Too many of them, he says.
He tells me his theory. In an agrarian economy, life was slow. Hence low expectations and distractions. Then came the industrial economy and a little bit of stress was added to our lives. Now we live in a hyper-connected, fast-moving world and thus we end up having mental issues. He said our lifestyle Fair. Possible. Believable.
Close to 40% Indians have a shorter-arm version of chromosome in the serotonin-transported gene. It means 40% of us are susceptible or more likely to suffer clinical depression after a stressful life event.
In 53 diverse cultures including hunter-gathering communities suicide has been documented. Right from Ache of Paraguay or !Kung of southern Africa. So it’s not modern or concentrated.
Human evolution most likely can give us insights or behind-the-scenes of depression.
Theory #1 Controversial statement: Evolution is an adaptation; not disorder.
Adaptation? Yes, every adaptation has a benefit and a cost.
A bit technical. A molecule goes by the name of 5HT1A receptor. This molecule can turn on depression.
What does 5HT1A do? It binds to serotonin. This serotonin is the target for anti-depressants to work on a depressed patient.
Rodents lacking this 5HT1A receptor have shown fewer symptoms of depression when exposed to consistent stressful environments.
The receptor in the rat and the human brain has a 95% match. It means the receptor has been passed on in the natural selection. Hence, it is not a disorder but a function that has helped humans to survive and reproduce.
So the next question arises- how is it a function and what’s the benefit?
To know this, let’s understand the symptoms- social withdrawal, trouble carrying out daily activities, no pleasure from otherwise pleasant activities, lethargy to physically move or uninterest in many activities.
Studies show depressed people often think in a highly analytical way about their problems. The problems are many times complex and spread. Hence they break it down into components and ruminate on solving the component in the expectation to find solution to the entire problem.
In fact, research shows people who get depressed while solving complex problems tend to score high in intelligence tests.
To solve complex problems, your brain cobbles for an uninterrupted sequence of thoughts. It tries to keep all distractions at bay. Like eating, daily activities, meeting people, talking to them on phone, chatting or even physically moving. So depression ensures we get that. That’s why the symptoms.
When a stressful life-event happens, your brain is left to solve with a bigger, complex problem- what next? what does this mean? how should I respond?
Now to concentrate on the problem the mind is solving, it constantly needs neurons to fire in a brain region called VLPFC * to remain undistracted. If there’s continuous firing there’s the risk of neurons-damaging. The hero- 5HT1A balances out the two: supplies fuel for neurons firing and prevents neurons from getting damaged.
This is why from an evolution pov, the 5HT1A receptor is useful and has been picked up by natural selection.
Hence the solution suggested is to allow depressed people to ruminate in a controlled environment rather than to prevent them from thinking so. An intervention such as asking them to write about the complex problems and soon they get an insight into their problems offering a quicker solution.
But many times, people don’t find it interesting to share the problems: they feel it’s too trivial, silly, unempathetic and they may find it difficult to put into words.
Theory #2 Depression is a maladaptation
Imagine a hunter-gatherer foraging in the forest collecting roots and berries or looking for a kill. There’s a lion keeping a watch on him. There’s silence the birds and other animals have gone quiet. It’s odd he thinks and from corner of his eye, he catches a glimpse of a lion-like figure. It is a lion.
His brain releases stress hormones and he doesn’t care if he’s got the lunch or is he taking pleasant smelling flowers back to his girlfriend. He has to flight or fight. His limbic system decides even before his conscious mind can know and he climbs up the nearby tree on the top-most branch.
The wood is rough and scratches his skin in the process, but he has to get to the top. In the process, the same part of his leg gets scratched further. He waits till the lion goes away and later gets back to his tribe. By then, the scratch became a wound and will soon get infected. His fellowmen have seen if the wound looks weird, is a mix of red, white, yellow then there are chances others might also get the same. So he’s advised to an isolated place, temporarily relieve him of his hunting duties and put him on a selective diet.
The guy keeps remembering he just missed being dead and getting thrown out of the gene pool. Now he has to recover from the infection.
Now when he’s into quarantine, certain genes (alleles, in this case) enhances his immune response to infections. The flip side, however, is at risk for depression.
Depression? How?
A bit of science. Many of us today have mutated gene of NPY that helps reduce inflammation during infections- which is nonetheless termed as depression. People who had the mutated NPY genes tend to fight better against infections and pass on to the next generation.
And also, studies have found people with depressive orders have this mutated NPY gene. Those who don’t have this mutation tend to fight stress better with increased tolerance levels but had the ancestors of these people would probably not have fought infections as good as their mutated NPY gene counterpart.
What it also brings out, is for survival, for more than 100 thousands of years, humans have battled infections. Infections have been one of the leading cause of deaths until recently after the improvements in public health and medicine. In 1900, the top 3 causes of death in the U.S. were via infectious agents: pneumonia, tuberculosis, and diarrhoea.
So your immune system fighting infections effectively is important more than anything else.
Hence depression helped them adapt and survive. Staying isolated and limited physical activity meant the following:
- Avoid getting more infections
- Avoid spreading infections
- Rethink about your life and come back fresh
For them, acute stress= physical harm or physical wound.
Now it’s no longer the same. The acute stressors are anything but infections.
And there’s no inflammation as well to fight for, but the brain coaxes the immune response to conserve energy. It is still thinking there’s infection to fight.
Hence the withdrawal symptoms and loss of interest. It’s all energy conservation. Hence a once-upon-a-time good thing is now a gross disadvantage!
Is there a solution? Without going technical, yes. How does your brain identify an acute stressor? By inflammation, and then immune cells huddle for a response thinking it’s infection. A drug named Infliximab cuts off the communication between immune cells and reduces inflammation. But it’s still underway.
Both theories give us an evolutionary insight into depression. I have been confident that human behaviour has its root in evolution and it hasn’t been a disappointing belief to hold.
*VLPC- ventrolateral prefrontal cortex
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