I recently read a book by Jonathan Rottenberg, who describes depression as part of the mammalian mood system. The human mood system is designed to drive and shape behaviour – it pushes us in positive directions and away from bad ones. For example, if a bear is fishing for salmon in a spot that is usually really good and no fish appear, that bear will experience frustration and unhappiness. This mood state will cause him to stop trying to fish in that spot and look for anther one. If he finds fish elsewhere, his mood system will reward him with positive emotions.

With humans, if you set yourself difficult-to-achieve goals, or undergo extreme stress, your mood system will shift downward. It’s trying to tell you something, but you may not be as in-tune with your moods as the bear is, and you may not listen. If not, the mood system will downshift your mood again and again, until eventually you either adjust your goals, or become totally incapacitated by your mood. If you don’t pay attention to low moods and learn from them, they will stop you in your tracks.

The mood system knows much more than we do. It has inside information on the health of our bodies, information that we don’t have access to. If, for example, we are deficient in an essential nutrient, or we are severely sleep-deprived, or we are being bombarded by too many demands, our mood system will take all of these elements into account. If we set crazy, unrealistic goals, our mood system will do everything it can to stop us, and turn us onto a better path.

We are sometimes like a frog in a pot of  water that has been set to boil – the water starts out cool, but over time, it gradually heats up until we are boiling. Our mood system knows that pot of water is going to boil eventually and, if necessary, it will scoop you out and toss you to safety, where you might lie for months, wondering why you feel so bad. But at least you’re alive! The mood system gives you signals meant to influence your choices so that you survive and even thrive.

While our mood system sees clearly, and sends us clear signals, our society often places greater value on other signals that override these vitally important ones. Many of these other signals come in the form of prescriptions – you should be successful; you should be happy; you should be rich; you should be thin; and so on.

To go back to the bear analogy – what if the bear could be convinced that if he just kept on fishing in the unproductive spot on the river, he would one day catch the biggest salmon ever? What if the bear believed that if he didn’t catch that salmon it is really his fault – that he wasn’t a good enough fisher? What if he thought he was weird for feeling depressed about his situation and then started worrying about not being happy?

If the bear listened to that kind of talk, he would probably persist in fishing at that unproductive bend in the river until eventually he became so depressed he had a nervous breakdown and crawled into a hole for a long time. When he came out later, he would hopefully find a better place to fish.

But here is the hard part: we don’t always know we are doing things that are dangerous to our well-being. As Rottenberg points out, we live in a time and place that is a perfect storm for low mood.

We hardly get any sunlight and spend all our time indoors. We get far too little sleep, on average. Our diet and exercise patterns are poor. And I would add that modern living forces us to synchronize our biological rhythms to a very fast-paced work world – we have to show up on time, every day, week after week, year after year. All of these factors, and many others, affect our mood.

For these reasons, Rottenberg says that we are now experiencing a depression epidemic. Depression may protect us from futile, often dangerous behaviours, but it is a very costly adaptation. Depression can be even more difficult to deal with than the situation that triggered it. To recover you need help from doctors, therapists, friends, family and often medications.

It is a very difficult, but productive process, where you learn about yourself and grow as a human being. By listening to depression, you discover yourself and the world anew. Ultimately, Rottenberg’s understanding of depression is a very optimistic one, because although he makes clear that there are many ways to become depressed, there are also a great many ways to recover from it, and all of them offer the potential for growth and renewal.