For Mental Health Month, I intended a linear progression through history. I began with the Dawn of Man, and it seems I’m still stuck there. Who knows? I may never get past 700,000 BC.

The reason speculation about our ancient ancestors is so important is that it forces us to think differently about mental illness. According to evolutionary biologist Randolph Nesse MD of the University of Michigan: "Psychiatrists still act as if all anxiety, sadness, and jealousy is abnormal and they don't yet look for the selective advantages of genes that predispose to schizophrenia and bipolar disorder."

The key word here is “tradeoff.” The sickle cell gene, for instance, is protection against malaria.

I heard Dr Nesse speak several years back at the American Psychiatric Association annual meeting. The selective advantage of anxiety was his focus. Obviously, sufficiently anxious cave men and women were able to steer clear of predators long enough to find an opportunity to pass on their genes to the next generation.

The snapping of a twig behind the caveman could have come from a mouse or a tiger. In either case, panicking first and thinking later was not such a half-bad idea. Even today, anxiety is crucial to marshaling our wits. We could never survive one day in traffic without it, let alone the full range of personal interactions.

The 1000 false alarms we experience, according to Dr Nesse, are the price of survival. Better to be too anxious. But there are limits. It’s one thing to panic at an ancient watering hole. It’s another to panic while reaching for bottled water in a supermarket. In other words, there is a clear distinction between anxiety and anxiety gone wild.

In speculating on the selective advantage for bipolar, it’s easy to imagine highly energetic and productive and creative types discovering fire and painting cave walls. It’s also easy to imagine them getting stomped on by mastodons and booted out of the tribe. Again, we’re talking about trade-offs. No one ever said bipolar was easy.

Thinking of a selective advantage to depression is far more problematic. But the evolutionary biologists have theories. Depression, for one, is when the rose-colored glasses come off, when reality sets in. It opens the way to acceptance, to setting new goals and moving on with our lives.

Also, sometimes it’s helpful to be too depressed to press our luck. If mania is all about daring, depression is about caution. The daring have an advantage in life's ultimate prize, the opportunity to mate. So do the cautious.

Depression also provides an opportunity for regrouping and recouping, not to mention a time of introspection and reflection. Think of depression as an enforced time-out. In its own perverse way, depression may set the stage for needed psychic healing.

But of course depression can also kill us. Trade offs, trade offs.

The selective advantage to schizophrenia is far more problematic. As Dr Nesse informed me, “any creativity advantage to compensate for the huge fitness costs of schizophrenia” seems highly unlikely. Rather, the question to ask is “why does the mind fail in this particular way so often?”