First, distinguish between catatonia and rumination
Jerry Coyne took a look at a hypothesis that depression is an evolutionary adaptation.
in two new papers by Andrews and Thompson. In short, their “analytical rumination hypothesis” (ARH) proposes that the “malady” we call depression is actually an adaptive behavior built into our ancestors by natural selection. When facing difficult social problems, selection is said to have promoted behaviors that make individuals withdraw from life, ceasing to engage in formerly pleasurable activities like socializing, eating, and sex. This is all in the service of rumination: freed from other activities and commitments, the depressed individual is said to analyze the problems that led to depression in the first place, eventually solving them and re-entering society. This is “adaptive” because individuals who lacked the depressive syndrome would not be able to solve their life problems so easily, and would leave fewer offspring than individuals who shut down and ruminated.
Part of what’s so interesting about that is that it’s so strikingly implausible on the face of it. (There’s no surprise ending – Jerry doesn’t say aha but it’s more plausible than it seems, and commenters are nearly unanimous in being unconvinced.) It seems to be pretty common knowledge that depressed thinking is bad thinking – distorted in many ways, and monumentally unhelpful for any kind of functioning. (As Jerry points out, there is the little matter of suicide for instance.) Mind you, depressed people are better than non-depressed people at giving a realistic assessment of their odds of getting in a car crash and the like, and also at avoiding the Lake Wobegon effect – but that seems to be the only accuracy-enhancing payoff. Other than that…depressed thinking is crap! It’s not the kind of thinking that helps people analyze the problems that led to depression in the first place and then solve them. That kind of thinking depends on not being depressed. I’m aware of this just from common or garden bad moods, so I’m also aware the effect must be orders of magnitude worse in real depression. I’m also aware of that from having been around depressed people – they are not humming with useful rumination and problem-solving, to put it mildly.
All this seems too obvious to mention – like saying that rain makes things wet. So…it’s interesting that Andrews and Thompson think it isn’t.