If you remove "lighter" schizophrenic people from the equation, the whole thing starts to look more like immortality. It's just that it's not too common yet.

And then there are those factors that cause depression. We should not give them authority either.

Taking into consideration how evolution works, might help with difficult questions like this one. Only those characteristics that lower a person's chance of reproduction or the chances of survival before reproduction, get eliminated by natural-selection processes. Hence, not all bad habits are left out by evolution. For example, although unpleasant, nail biting doesn't restrict a person's chance of reproduction or survival up to the age that they can reproduce. Smoking and bing eating or drinking are in the same category; although really harmful, they do not affect reproduction chances hugely.

I see. Thank you for clarifying.

So by this mechanism if self-harm has any genetic aspects they could remain in the gene pool so long as they didnt result in genital mutilation, castration or any harm that damages the chances of reproduction.

I would suspect you would see higher rates of suicide in older adults then except the youth are disproportionately more vulnerable so self destructive tendencies must be largely influenced by nurture and environment over genetics.

As far as I know, all animals have an instinct for self-preservation. This instinct has been safely lodged in our genetics since time immemorial. It is not going to be selected against anytime soon, IMHO.

Sometimes this instinct is overridden by other instincts. For example, the male black widow spider who mates with the female even though he will most likely end up being eaten by her. Or the female salmon who hurries to her spawning ground even though she will die soon after getting there.

As human beings, we are not fully controlled by our instincts. We are capable of acting against them. That's why a fire fighter, for example, will go into a burning building even though his instincts tell him not to. Or a mother risk her life to save her child.

We have the capacity to act against our instinct for self-preservation. We seem to do so when we have a more compelling personal reason overriding our self-preservation. We label such actions as self-harm when the reasons seem to motivated by mental illness.

Why should it ever have a tendency to harm its body if it were to be just the product of biological evolution and natural selection. As far as I know natural selection does not select detrimental/life destroying tendencies. Why does the brain have this ability to destroy it's own existence/ obliterate itself and or its body and what is the reason this self destructive capacity ever developed in the first place? — Benj96

Those with detrimental/life destroying tendencies can still reproduce before these characteristics manifest and cause the end of the organism's life.

From the point of view of natural selection, it matters not whether an organism lives a hundred years or two minutes, or if its life is filled with joy or agony, so long as the organism successfully reproduces.

From the point of view of natural selection, it matters not whether an organism lives a hundred years or two minutes, or if its life is filled with joy or agony, so long as the organism successfully reproduces

This is not the whole story. Natural selection is properly understood as acting on populations. All other things being equal, the portion of a population undergoing some agonizing stress will reproduce less successfully than that portion of the population not experiencing this stress. This is assuming that the stress manifest itself in such a way as to negatively impact pre-breeding survival rates.

I think the distinction between brain and mind should be made. The mind will be able to override those instincts as has been said above.

Perhaps the better question to ask is: Why do people do these things?

The brain has a general reward system with both innate and conditional capacities. For most compulsions, there is some feelgood chemical released by the body, e.g. dopamine, endorphins, oxytocin.

Innate reward systems tend to involve metabolism or reproduction. Heroin and nicotine, for instance, or fat and sugar. Availability would traditionally be a limiting factor so need for a shut-off hasn't generally affected our evolution.

https://en.wikipedia.org/wiki/Reward_system?wprov=sfla1

Some bad habits are conditioned, such as by validation. I don't know why people bite their nails, although I can see the evolutionary benefit of it once we stopped walking on our forelimbs.

A lot of it has to do with the fact that we operate in an environment that we did not evolve for.