If you subscribe to an evolutionary description of human psychology, then you will believe that most of our behavioral traits are actually the result of our evolutionary history. We are afraid of snakes because they would have eaten us in the wild. We are altruistic because it’s necessary for us to live in groups. And we find small things with big eyes cute because this encourages us to look after our own young (and thus our own DNA).
Thereby all of our psychological traits and all of our behaviors should have survival value and should have been selected for in order to be adaptable.
The question this might leave you with though: is why then do mental health problems exist? What is adaptive about being a psychopath? Or having a phobia? Or developing Alzheimer’s?
We’re Not Perfect
One argument is that we just haven’t ‘finished’ evolving. There are very few examples of animals that have been alive for millions of years without really changing and as such we might be still ‘finding our footing’ with regards to certain aspects of our psychological health.
Of course it can also be that something has just ‘gone wrong’. This might mean we’ve had bad experiences, or it might mean that something has physically changed in our brains that has caused us to ‘malfunction’ as it were. In this regard, an evolutionary explanation for our psychology does not preclude us from also accepting a biological explanation or a behaviorist explanation.
And in fact, small deviations from the norm are required for evolution to work at all. Evolution relies on small genetic mutations occurring that result in the birth of specimens that are slightly different. Those small changes might prove to be adaptive and thus they might proliferate within the group. On the other hand, the change might result in a psychological disorder. And indeed many psychological disorders have at least a genetic component and many appear to run in families – even things like bulimia nervosa (1).
The Selection Shadow
Age related cognitive decline and dementia and other progressive brain diseases are widespread and you might think that something so destructive would have been eliminated through natural selection. And while there are some genetic risk factors for late-onset Alzheimer’s disease (the more common form), researchers have yet to identify any single mutation that might be responsible (2).
But it may be that a condition like Alzheimer’s or another form of dementia doesn’t really apply when it comes to the ‘normal’ rules of evolution.
This might be explained by something called the ‘selection shadow’. The selection shadow describes the fact that evolution only pays attention to individuals that are capable of mating. In other words, the ‘directive’ of evolution is the survival of genes. Once you have successfully procreated, you have ensured the survival of your lineage and thus what happens to you after that point won’t have an impact on your ability to have passed on your DNA.
Thus there is no process by which late-onset Alzheimer’s or dementia could be eliminated by evolution. In the wild, being predisposed towards Alzheimer’s would have made you no more unlikely to breed successfully.
Finally, some of our mental health issues can very elegantly be explained as being ‘vestigial traits’. In evolution, a vestigial trait is anything that was once useful and no longer is. Our tail bone for instance can be considered vestigial – it once allowed us to use a tail that in turn helped us to balance in trees. Today we don’t need a tail, but we haven’t completely gotten rid of the tail bone.
But you can also consider some psychological tendencies as ‘vestigial’. For instance, widespread fear of spiders is something that would have helped us to avoid getting poisoned in the wild, but is not at all useful today. This is a ‘vestigial’ psychological trait. Likewise our ‘fight or flight’ response could be considered vestigial to an extent (or at least less adaptive to today’s surroundings than it was in our history). Seasonal affective disorder too is vestigial in as much as it would encourage less activity during the cold winter months (3).
Evolutionary psychology is not perfect in describing every one of our various psychological disorders and mental health issues then but it does have a number of means to explain why we might not always appear to be that ‘adapted’.