Depression as a fitness indicator

Scientists are baffled by the fact that in the last 50 years, the human race (or at least the US population) progressed and advanced in every single measure of life quality - diseases were treated better, people had better incomes, more education, etc. - but the rate of depression among people rose steadily in spite of all this. I have a new theory that will explain the weird phenomenon known as depression - it is basically a fitness indicator, like a peacock's tail.

That is why artists are prone to depression, according to this theory. They already have other fitness indicators, such as excelling in art, which requires a lot of leisure time. Depression, too, is expensive - it makes one's mood horrible, it takes up time and energy. One of the causes (symptoms?) of depression is catastrophisizing - you basically make a big deal out of small stuff. Think of this in the prehistoric setting... Everybody is dying, or losing someone they know because of famine, but this one very influential guy is depressed because "his favorite spear is broken." What a luxury! It is a wonder that depression rates go down in times of war. With this theory, that phenomenon is also explained.

Exercise is found to be as effective as anti-depressants: In old times, a person who had to run, hunt, and live off the land was a person with not much influence, they were peons. The chief, however, ordered other people to hunt "for him." He did not have to exercise or run, and he probably had lots of time in his/her hands to wonder about "the meaning of life", etc. The peasants do not have time for this kind of depression, they run (they have to), they eat, they live and die.

A theory is not complete if it lacks a solution to the problem it explains. This theory's solution for the depressed is to run, a lot.... Live off the land, do lots of physical exercise, with lots of other people. Depression is usually about status...

Of course, sometimes depression comes after a bad event, in this case, of course, "catastrophisizing" is not in "vain", for the lack of a better word. So this theory may not explain every blues, melancholy, dysthymia, etc.

Now, depressive people will accuse me of "making light" of an illness. But the fact that it is a fitness indicator should make these people feel better. These people may feel worthless, but in actuality, their brains make them think that way, like a magnificent piece of art.