Spectacular! At last, a rational examination of depression from the "mood science" perspective. Weather your a clinician, or just a regular joe suffering from depression and looking for a way out, this book will be useful.

The author's arguments are grounded in experimental bio-psychology and evolutionary theory. The author posits that (what we currently refer to as) depression is an adaptation rather than a disease.

Although severe depression may be maladaptive in our current social and economic environment. The same trait is conceivably within the spectrum of behavior, between adaptive organismic up-regulation (expend energy) and down-regulation (conserve energy).

The obvious metaphor being the gas and break systems of a car. Where so-called manic symptoms represent the "go" gas and depressive symptoms represent the "stop" breaks. As every driver knows, sometimes slamming on the breaks keeps you alive.

For example:

Seasonal depression, is conceivably an adaptive response to the predictable lack of resources and opportunities in winter months.

In other words, it would have been adaptive for our ancestors to down-regulate and conserve energy (i.e. lay low) in the winter. This would be akin to hibernation in other mammals.

What we now experience as debilitating malaise could have been adaptive in the ancestral environment.

Postpartum depression may be an adaptive "authentic signal" i.e after giving birth, it may be adaptive to display overt signs of distress in order to garner needed social support for the task of tending to the infant during the critical early months of child rearing and during the mother's convalescence period.

After a significant loss it may be adaptive to "slow down" and skeptically reassess your life trajectory before rebuilding in the next period.

In times of danger, when things are actually hopeless and you are actually helpless to change the situation, it would obviously be adaptive to "hit the breaks" ", hide out, and conserve energy while the danger passes.

Things get sticky when this adaptive trait interacts with our other very human adaptation, language (and imagination). Sometimes the dangers we fear are neither clear or present, and sometimes our distorted beliefs and "negative self-talk" can "dump gasoline on the fire of otherwise healthy down-regulation.

Additionally, our current social and economic environment permits longer periods of inactivity than our ancestral environment likely did. Allowing depressed individuals to do things like not exercise for days, months, years etc. More gas on the fire.

Similar to the way our ultra efficient fat storage systems kept our ancestors alive in time of scarcity. But is now a public health crisis in our current environment of abundance. Depression may have kept our ancestors alive in an extremely dangerous and competitive environment. But is literally killing us in our current economic environment of go, go, go or sink like a stone.

Many object to evolutionary psychology as essentially "just so stories". But this is actually not so. To paraphrase Richard Dawkins, just so stories are Lamarkiean (a little evo-humor for the initiated).

Evolutionary theory is communicated in story from to lay people. But it is investigated via the methods of anthropology, tested experimentally and modeled mathematically.

The theories become the basis for hypothesis that are later tested experimentally and are subject to the same processes of peer review and replication as any other experimental claim. It's not perfect. It doesn't "prove" anything. But neither does a lot of legitimate science.

In many cases, including much of physics, science is simply our current best guess based on what we can currently know, and based on how our predictions pan out experimentally. This is all very consciously subject to revision as the data continues to accumulate. Real science never claims to prove anything. Real science is necessarily sceptical, especially of its own findings.

If you're sceptical of evolutionary psychology, good. But now it's on you to come up with a better explanation, and a more predictive model. Go for it! We'll all be better off for it. But if your an armchair hater, all I can say is, I hope you have fun on the trailing edge. These exciting new perspectives on human behavior are revolutionizing the field, and becoming more mainstream daily.

For the life of me, I can't understand haters of evolutionary psychology. I'm tempted to venture a guess or two. But I have been drinking, so now is not the time to wonder down that dark alley. Suffice it to say that if you are an evo-psych hater, you may wish to opt out of this one (at your own experience).

If nothing in biology makes sense outside of evolutionary theory (and it doesn't), than we can safely include human behavior, cognition, and affect in that camp. Last time I checked, people (including our brains and our behavior) are biological, and are probably not somehow magically outside of the same evolutionary process that shaped all other things biological.

In conclusion, The Depths is an important and clarifying read. Comprehensive yet brief, very well researched and written. I highly recommend this tight little book.