Why Did Evolution Produce Depression?

Why did evolution give depression such a foothold on human psyches? If it's bad for us — and it's known to have health consequences and lead to suicide in some cases — it should have worked itself out of the gene pool long ago.

Well, maybe depression's not such a bad thing.

"We argue that depression is in fact an adaptation, a state of mind which brings real costs, but also brings real benefits," write Paul W. Andrews and J. Anderson Thomson, Jr. in Scientific American. They cite some complex chemical explanations and also point out that depressed people are very good at thinking intensely about a problem in a highly analytical fashion — a good thing.

Meredith Small, an anthropologist at Cornell University, suggested similar explanations in a LiveScience article last year:

"Obviously, sadness is part of life for animals with big brains," Small wrote. "The capacity to feel presumably helps us solve problems and survive, and is essential for group living, and perhaps inconsolable depression is simply emotional baggage that tags along with the good stuff. Or maybe unhappiness and a tendency towards suicide is the product of the uncontrolled nature of our quicksilver minds. We think a lot, and our wondering minds are just as likely to think sad as happy."

Depression is one of many conditions that make you wonder. Insanity is another.

"Natural selection wants us to be crazy — at least a little bit," wrote science feature writer Robin Nixon earlier this year. "While true debilitating insanity is not nature's intention, many mental health issues may be byproducts of the over-functional human brain."

Nixon cites researcher David C. Geary, author of "The Origin of Mind," who thinks that as human populations increased back in hunter-gatherer times and as farming developed, we had to evolve new social skills of cooperation. "A diversity of new mental abilities, and disabilities, unfurled," Nixon wrote.