Which states of mind that are classified as mental illnesses might be a natural and useful part of our brains?

For example, some evolutionary biologists have suggested that some types of depression are a natural consequence of losing a fight for dominance. i.e. In order for the loser to fit into the social pecking order he must have feelings of low self worth.

Are there other types of "mental illnesses" that might be natural and useful? (By "natural" I simply mean evolutionary selected for.) And that if this illness was cured for all human beings it would in fact damage the social fabric of society?

Another example. A phobia of spiders. Most people would agree that this is not a mental illness but a common trait of most humans. A phobia of trees is probably not.

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    $\begingroup$ Or a more provokative example: Suicide. Some argue that this is an adaptive behaviour functioning on kin selection, triggered when someone implicitly feels like they are more of an burden than an asset to your kin. $\endgroup$
    – Alex
    Jul 21, 2018 at 16:10
  • $\begingroup$ @Alex It's an interesting theory, except that I wonder how it would work in caveman times. Perhaps throwing oneself in front of a wolf. $\endgroup$
    – zooby
    Jul 21, 2018 at 16:15
  • $\begingroup$ Or throwing yourself down a cliff? Like bridges or skyscrapers... $\endgroup$
    – Alex
    Jul 21, 2018 at 19:23
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    $\begingroup$ A word that is more fitting than "natural" for your use is "adaptive." I doubt that depression has been adaptive; sure, some level of reacting sad to certain situations and a certain level of rumination, but not full-blown depression. Depressive individuals appear to have lowered reproductive success presently. While that doesn't guarantee that it also lowered fitness in ancient times, it is an indicator. Depression also has a mutational load or paternal age effect. Increased mutations increases risk of depression. I recommend reading this. $\endgroup$
    – Eff
    Jul 21, 2018 at 22:54
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    $\begingroup$ This is not a good question here because it asks for a (potentially very long) list of things, with accompanying arguments/papers. Probably any mental disorder has been argued by someone to stem from an evolutionarily advantageous process. Look for example at evolution.berkeley.edu/evolibrary/article/medicine_05 Also the title of the question seems to have the implication that some mental disorders are "artificial", which is actually a completely different discussion (classification etc.) $\endgroup$ Jul 22, 2018 at 0:28