One of the paradoxes of the modern age is plummeting global poverty matched almost perfectly with rising clinical depression. Like never before we can defeat diseases, survive childbirth, elude predators, avoid war, and enjoy leisure, yet never before we been so unhappy. How can this be?
A possible answer comes from Maslow’s Hierarchy of Needs, a simple pyramid of human motivation from basic survival, through safety, to self-actualisation.
Since moving towards a goal releases dopamine – the fuel of positive emotion – our happiness is closely tied to the nature of our goals.
When we have nothing, they are crystal clear: get food, get safety. But with those achieved, we move into the rarefied air at the peak of the pyramid where our goals become more complex and abstract. Safe and well-fed, we seek identity, purpose and meaning, and happiness becomes maddeningly elusive.
Robbed of tangible goals and easy dopamine, modern humans are sitting ducks for depression.
Depression is a kind of sadness gone rogue, “a nausea of the cells and soul” that strips the senses of all life and colour, stifling all positive thoughts and stymieing every helpful action.
Depression is a response to life’s problems that becomes a problem in itself, making solving those problems even harder than before.
The truly depressed person cannot seek food, shelter or mates; they cannot fight or take flight; they cannot reproduce; they can barely survive.
Imagine a similar condition among birds called Heavy Feather Syndrome, dragging the afflicted from the sky and keeping them grounded for weeks, months or years. Natural selection would rapidly whittle the rate of HFS down below 1% or extinguish it entirely, either that or the whole species. Evolution simply won’t suffer such a flaw to live.
So why would life evolve something so counterproductive in humans?
Parallels with animal kingdom
A vital clue comes from curiously depression-like responses among animals. A male lion who loses a duel, for example, will slink away to lick his wounds, showing little interest in the pride, losing energy and appetite, and avoiding further fights or potential mates.
The lion is behaving like someone depressed – and it works. If he leapt back into the fray immediately, another defeat and possible death would quickly follow. By hiding away he can recover and regather his strength, and one day soon he will be ready to pounce once more.
The lion’s response is like an extended flight response. In the classic fight or flight response, the pupils dilate, the heart races, blood pressure goes up: the body gears up for rapid and vigorous action.
This is an excellent idea if there is a fight to win or a danger to flee, but for an animal that is trapped, wounded, or outmatched, ramping up the system for rapid action only makes things worse. Vital energy will be expended and injuries exacerbated.
In situations where an animal faces a serious downturn with no active way to respond, such as by losing its mate or getting knocked down the social hierarchy, the best solution is to withdraw, to play it safe – like a defeated lion licking his wounds or a lobster slinking away in submission.
These withdrawal responses are universal throughout the animal kingdom – so could depression in humans be just this kind of safety reflex?
Depressed humans also shut down and withdraw. They hide away, stay in bed, don’t socialise, don’t take risks; they lose their interest in sex and food. All behaviour is dialled down.
When it comes to all the beneficial but risky activity of normal life, a depressed person just doesn’t feel like it, or see any point in it. Neurotransmitters are pumped out or shut off, receptors are up or down regulated, genes are switched on and off and this chemical cascade produces horrible thoughts and feelings.
A lack of interest and energy, a loss of confidence, the presence of mental pain – all of these feelings act to make a person hide away.
We can also see a strong cognitive element, with ruminations about past experiences and present problems that are equally involuntary. Together, the different aspects of depression all seem to produce a withdrawal response which forces contemplation of what went wrong.
If with look at depression through the eyes of evolution, the response starts to appear not so pointless after all.
If this depression is the same response as in other animals, then there should be biological parallels, and this is precisely what researchers are discovering.
Similar neurological pathways to depression
The same serotonin 1A receptor involved in human depression is 99% identical in rats, while depressive responses appear as far down the evolutionary chain as crustaceans, who separated from our line some 500 million years ago.
A lobster with high serotonin responds to a nudge with a fight posture, but a low-serotonin lobster responds with submission. If this second lobster is treated with a serotonin solution, suddenly he will fight with anyone.
Withdrawal and submission responses in the animal kingdom appear to be triggered by threats where fight or flight is impossible or pointless. If we look closer at the conditions that lead to human depression, we see strikingly similar features.
Situations that provoke a sense of entrapment, humiliation or loss are especially potent. Some experiences, such as being sacked or suffering infidelity, deliver these three elements in one convenient bundle.
Often the person may find a tangible target and here anger stimulates action, but at other times there is no-one to blame and no clear path. Here a temporary shutdown can conserve resources and prevent an unwise, unfocussed response from making matters worse.
Not knowing what to do or where to turn, every choice seems equally horrible. Unable to respond, it feels safer to bunker down, to face no threat and seek no opportunity, to hide away, watch the same TV show, eat the same food, stare at the same wall.
Depression is the response when external chaos is so overwhelming that the mind desperately seeks a return to simple order.
And so we can see strong parallels between depression in humans and the withdrawal response of the animal kingdom. But questions remain: what turns a helpful adaptation in animals into a debilitating disease in humans? Why is it that a lion can rebound into a fray after a week, but a human may be paralysed by a crushing melancholy that lasts years?
We shall tackle these questions in Part 2.