Running on Corrupted Hardware
Your subconscious brain has strong opinions about how you should live - and they're often wrong
Trauma, depression, akrasia, suicide, addiction to junk food, and many common mental health "illnesses" are most likely not illnesses.
They are adaptations that are being activated.
Abuse (sexual, physical, emotional) doesn't directly cause trauma in the same way that a knife wound causes a scar. Our brains are deliberately wired to go into a trauma-mode following abuse.
Abuse or inappropriate treatment at one point in life (particularly as a child) can lead to what we politely call “issues” later in life, issues like anger, infidelity, depression, prickliness, borderline personality disorder, etc.
These "illnesses" are nature's way of adapting a person to what nature's best guess about the environment is. Whilst some mental problems may be caused by pathogens like toxoplasma or may be genuine malfunctions, common mental problems that affect >1% of the population are most likely adaptations.
Zoom out a bit and think about it like this: your unconscious mind has been mercilessly optimized by evolution.
It would probably be easier for the adult brain to have a personality that simply couldn't be "damaged" by abuse (a constant is simpler than a variable!) ...
... so why aren't we like that?
Because that wouldn't be evolutionarily optimal: the people who didn't adapt based on these signals were less able to survive and reproduce in the past.
Consider obesity. In the past being somewhat fat was likely highly adaptive, as that stored fat could be used to survive through harsh times (famine).
But being seriously obese is not adaptive. People with huge stores of body fat die young and are unable to reproduce, even in the ancestral environment a BMI of 60 or 70 would not have been good.
The brain does this on purpose, it's maladaptive, why?
Why not have a biological system that measures how fat the body is and stop the food-cravings once the fat level exceeds a certain point? That would lead to an objectively better organism!
The answer is that in our ancestral environment (as hunter-gatherers and to some extent as peasant farmers), population was largely limited by food. If there was excess food, new people would be created to eat it. This would happen until people started dying of starvation. So the food supply conditions that create the opportunity for morbid obesity were reliably impossible in the past. It is only really in the last 100 years that we have had sufficient food for everyone, all the time.*
It is also only in the last few thousand years that even some places have had reliable rule of law, and only about 100 that we have had police, distant travel for all and a uniform "society" that was out there for anyone.
I believe that the historical rarity of fair, uniform, large environments are largely responsible for many common mental health problems. Being traumatized by violence or abuse is an adaptation, an act of learning, that is preparing you for life in a violent place (likely low down in the hierarchy). Historically being traumatized by adversity was probably the right thing to do. Nowadays - at least in most parts of the civilized world - it is a huge mistake.
* (Even that is something of an exaggeration - it’s only very recently, since perhaps 1960, that almost everyone in most parts of the developed world had the option to become obese. The danger from overeating is extremely new and we are very poorly equipped to deal with it.)
** (If you’re interested in diets in particular, you should probably read the slatestarcodex review of The Hungry Brain by Guyenet. Guyenet basically argues that the body has a fat-storage homeostasis system which is “thrown off” by modern delicious diets, though I suspect that this is more like enemy action than like an accident; your body is trying to get you to store surplus food from the good times, but we live in permanent good times)