Last week's New York Times magazine had an interesting evolutionary psychology article about the debate over whether propensity for depression might in fact be an adaptive trait. If you've never thought about evolutionary psychology before, it's a good introduction. The premise of the article is that a large proportion of the population appears to be prone to depression- yet, depression would seem to interfere with our ability to survive and reproduce, so why did we evolve this way? The main argument is that depression may serve an evolutionary purpose as a mechanism to get us to think deeply about our problems and learn from our mistakes. An important feature of depression is "rumination-" obsessing over negative thoughts to the exclusion of anything else, and maybe that process helps depressed people make better decisions in the future.
I was a bit unconvinced by that- as the article points out elsewhere, there's more to depression than just rumination, much of which seems obviously maladaptive. More intriguing I thought was the argument that the evolutionary explanation for depression might have to do with avoiding conflict over social status. The idea being, depression protects people with low status from themselves by making them sit around and mope all day, intstead of trying to gain status by opposing high-status people and potentially getting killed in the process.
Related to that, I wonder if the evolutionary function of depression might be to regulate our perceptions of our own self-worth according to circumstances. Most people, most of the time, seem to have inflated views of their own capabilities. Whereas, depressed people are the opposite. From an evolutionary standpoint, holding an inflated view of one's own capabilities might be useful in that it helps with signalling to potential mates. The more you believe in yourself, the more you can convince other people how great you are and the more you can reproduce. But, there's a countervailing cost in terms of survival risk. Overestimating your own ability can lead you into a miscalculation that gets you killed- say, by believing that you can successfully challenge someone who is in fact much more capable than you are.
So which wins out? Is having an inflated view of your own capabilities adaptive (i.e., are people with inflated views of themselves more likely to survive and reproduce than people with more accurate views) or not? Maybe the answer is, "sometimes." Under normal circumstances, the evolutionary pros of being overconfident outweigh the cons. But if things aren't going your way- for example, if you end up with low status, or your environment places you under constant threat- then the dangers of miscalculating outweigh the reproductive benefits. Depression is how our brains tell us that it's time to start being more realistic about coping with potential dangers, and to stop trying to puff ourselves up to attract babes.
More broadly, it would seem to make a lot of sense if people have the capability of assuming either high social status roles or low social status roles as circumstances warrant, rather than social status being completely determined by inherent traits. The overconfidence/depression combination might be a way of maintaining that flexibility- depression makes someone who would ordinarily seek high status to accepts a low status role.