Nick James at the Trajectory podcast

Evolutionary Psychiatry

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A few weeks back I mentioned Randy Nesse in the context of his aside about ageing. Long story short, I was so impressed by this guy’s discussion that I bought his book Good Reasons for Bad Feelings. His angle is to look at how evolution accounts for the most complex aspects of human biology. I’m loving it. His focus is looking for evolutionary reasons for psychological conditions. You might think that would be nothing new, though he points out that it was something very new when he picked up his interest in it half a century ago. Surprisingly, it still is a relatively uncommon way of looking at psychological disorders. And thirdly people often misunderstand the mechanism in ways I will refer to. 

Something I admire – try to aspire to myself and routinely find tough – is finding simple metaphors to illustrate complex things in a clear way. And I would give Nesse at least eight out ten for this. What he is dealing with is fearsomely complicated, and he comes up with some beautiful metaphors, perhaps the smoke alarm is his best one. However complexity still rises like the morning mist to blur the light of dawn (see what I did there?) Anyway – the discussions make so many turns that it’s still fairly easy to get tangled up. 

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So I’ll cover the smoke alarm illustration since I have mentioned it. He’s talking here about anxiety. Anxiety is universally seen as a problem, but he points out that people without anxiety die young – and maybe back in the day that might have meant too young to reproduce, so it’s a good trait to have at least a bit of. Then he points out that smoke detectors sometimes give false alarms. They give false alarms more often than they fail to operate when there is a fire. If they never gave false positives then the range at which they are sensitive would have to be set artificially high on the risk spectrum. That might, or probably would, allow more fires to start without setting off the siren at all. Thinking about it, a false positive alarm is a minor annoyance, a false negative (ie a failure to sound the alarm at all) can be a disaster. 

Now,  think of your ancestor at the water hole. If she was anxious and thought that the rabbit in a shrub was a tiger, she might have wasted a few calories running away. But if she is so laid back that she assumes the tiger is a rabbit or even a really cool stripey cat, then she becomes lunch. That your ancestor survived means she was, let’s say, anxious enough, and quite likely a bit too anxious, but not far too anxious, otherwise she’d have died of thirst. Viewed in this way we should be grateful that evolution has gifted us the ability to be anxious, and hardly be surprised if it has left us with more false alarms than we would like.

Apart from giving us a neat academic explanation for one of the ways stuff might be as it is, he points out that it can be surprisingly therapeutic for someone suffering from chronic anxiety to be able to see their own situation as a poorly adjusted but necessary alarm mechanism rather than (wholly) as a pointless damaging disease. 

So, what about the ancestor who would have died of thirst if her anxiety was tuned so high as to make her nothing but a bag of nerves? Well there will always be outliers on the bell curve in the generations that evolved since waterhole days, and secondly in the modern era or actually at any time when there were social groups, maybe someone else would bring the water. And so it remains that the evolution of anxiety has every incentive to raise alarms at least as often as necessary, and it doesn’t have much incentive to care about being cool.

Another way he illustrates that anxiety may be a positive is by examining why women live longer than men. He suggests that women don’t actually live longer, it’s just that men tend to die young. He has written a paper about this which mentions ‘Being male is now the single largest demographic risk factor for early mortality in developed countries.’ Old men, he explains, don’t actually peg out much before old women. What happens is that silly young men accidentally kill themselves because they don’t have enough anxiety, and this brings the average down. (Women in these terms have about the right amount of anxiety.)

Now, sex and drugs and rock and roll are all most exciting for men at the same age as violence and extreme sports, so by the time our hero tops himself by jumping off a cliff in a batsuit, he has probably already done more than enough mating to propagate his lack of anxiety. 

I tried to check this thesis out by downloading life expectancy tables from the UK Office for National Statistics and they didn’t seem to confirm it. I graphed life expectancy as a percentage differential between male and female by age. Having taken account of Nesse’s statement, I expected the lines to start widely separated and then to sweep together just after the age when men stop being recruited to the armed forces. After that I thought that the small remaining  differential would perhaps taper away to zero just before the few remaining centenarians died. 

The difference doesn’t seem to behave like that though. Maybe there are other factors, maybe men don’t stop being life-threateningly silly until they are in middle age, or maybe my understanding of statistics is rubbish. As observed by Mark Twain in a famous statement generously attributed by him to Benjamin Disraeli – The study of statistics is a notoriously difficult area of basic maths to interpret correctly. If anyone would like to clarify this is a comment to me I’d be really grateful. I should mention that anxiety or the lack of it is not the only reason for early male mortality mentioned in Nesse’s paper. Maybe if I can’t work it out myself I’ll submit a query to my favourite statistician Tim Harford and report back here if I get a response.

Meanwhile three of Nesse’s recurrent threads are, 

* Avoiding what he calls VSAD or viewing symptoms as diseases.

* Avoiding the temptation to search for what gene causes what disorder. Better ask what environmental situation may have led to the evolution of a pattern of behaviours that increases evolutionary ‘fitness’ – inevitably by the incalculable interaction of multiple genes influencing emotions and hence behaviour.

* And his third recurrent thread is speculating on how what may have been a good evolutionary response has evolved into what are some of today’s most debilitating disorders. 

I have already given an example of the third one, so what about the other two?

That first one about viewing symptoms as if they are diseases provides a nice illustration of how he clarifies stuff, but it still remains fearsomely complicated. I don’t blame Nesse for this. If he oversimplified the subject with the risk of misinterpretation, that would be much worse. 

So on the subject of VSAD, he points out that psychological difficulties are widely considered to be diseases or disorders, but say coughing, or pain, or running a temperature are considered as symptoms. It’s easy to understand that physical symptoms have benefits. Pain helps keep you out of danger, coughing expels the mucus that your body makes to trap bugs, and fevers provide a better environment for your immune system to work fast. Once we realise that mental pain has a function similar to physical pain then it’s possible to consider where it came from and how to deal with it, maybe even whether to deal with it. 

But it’s still complicated. In physical medicine for example, there aren’t just symptoms and diseases, there are whole syndromes or collections of chronic symptoms again which don’t map neatly one to one against diseases. This muddies the water. And so it is with mental problems. The water here is already muddy, so it’s not an easy thing to clarify.

On the second line, that one about mapping mental problems to genes. He shows how a great deal of work has proven fruitless, and it shouldn…



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