Depression may be an evolved strategy for pathogen defense, linked to reduced iron, reduced zinc, and elevated body temperature.

“So it’s very striking that depression is so reliably associated with things like shunting your iron, or shunting your zinc, raising your body temperature, you know. So if you think about, you know, why would those characteristics occur in a condition like depression that we think of as being largely psychosocial, you know, if your girlfriend dumps you and you get depressed, it might make sense why you weep and cry. And, you know, maybe it be you sit down, and it makes you reevaluate your life, but why should it elevate your body temperature? Why should it cause your iron stores to be reduced? On the other hand, you know, if depression evolved out of sickness as a strategy for pathogen defense, all those things make a lot of sense.”