Is Depression a Biological Adaptation?

October, for some reason, has been designated depression and anxiety month. I have done a few interviews trying to promote my new book, “Yu, The Dragon Tamer.” Although the book is about mental illness, it has little to do about depression. But, because, I suppose, interviewers have to attach their interviews to various fashionable “hooks” most of them wanted me to relate this work to depression. I did my best to accommodate them but I am sure my response would have disappointed some of them.

I have decided to compensate for that short-coming in this week’s blog. I want to put to you some very controversial points of view about depression coming from the perspective of evolutionary psychology. In pursuing this controversial theme, let me ask the question, “Is depression an illness or is it a biological adaptation which confers (or at the very least once conferred) on some of us an evolutionary advantage – an opportunity to improve our reproductive success?”

Evolutionary psychology describes how an ancestral environment different from the one we face today shaped the structure and function of our brains. As a result, we have internalized aspects of our ancestral environment that may be ill suited to life today.

Depression is a huge and growing problem, particularly in the developed world. The World Health Organisation predicts that by 2020, unipolar depression will be the second largest health problem in the world.

If you are familiar with people who have suffered depression you would be aware that it is very debilitating. It is hard to reconcile this suffering with positive benefits in evolutionary terms. But one should remember that suffering is often helpful. Physical pain causes us to protect our bodies. Nausea helps us eliminate toxins from our bodies.

However it is instructive to understand how other primates have parallel experiences. Research by McGuire and Raleigh suggests that vervet monkeys possess a cerebral mechanism that connects their mood to societal status. The researchers found that dominant male monkeys had double the serotonin levels in their brains compared with other males in the group. When such animals lost their dominant status their serotonin levels immediately reduced and they were seen to withdraw and lose appetite.

Price and Sloman have argued that depression in humans could have been a behavioural strategy used by our ancestors who perceived they were of low social status to signal submission to the more dominant members of the group and thus protect themselves from harm. They postulate that this strategy in humans is demonstrated in three ways:

1. Inhibition of aggressive behaviour: diminishes the probability of attack by dominant members
2. Submission: informs the rival that there is no threat
3. Acceptance: submission encourages the individual to accept the loss of competition. This process brings reconciliation and the end of conflict

Some evolutionary psychologists point out the benefits that what we label disorders confer on us. Edward Hagen, a research scientist at Humboldt University in Berlin argues that depression, suicide attempts and deliberate self-harm are rational bargaining tactics designed to manipulate others into providing support they might otherwise withhold.

(This seems to correlate with the thoughts of Dr Phil Harker who in private conversations has stressed to me that human behaviour is best understood by trying to seek out its purpose rather than its cause. Looking at what happens after the behaviour is displayed is often more instructive than seeking to find what preceded it!)

One of the themes of evolutionary psychology is to point out how behaviours which evolved when we were hunter-gatherers and which then conferred on us evolutionary benefits may be quite deleterious to us in the modern world. When our lives were physically difficult and quite short, any behaviour that prolonged our lives by a year or two could be deemed beneficial. Many of those behaviours, which might still result in short-term benefits, can now prove harmful in the longer term. For example the typical “fight or flight” response which no doubt was invaluable to a hunter-gatherer faced with physical danger, now can result in cardio-vascular disease when our threats are no longer physical but more often threats to our self-concept. It would seem that depression might also fall into that category, conferring short-term benefits for some of our ancestors but with a long-term cost for today’s sufferers.

The difficulty that I have with the evolutionary psychology approach to depression is that even if depression were to confer some benefits resulting in the sufferers being cared for better or at least not attacked as much, the evolutionary penalties seem to outweigh the benefits. Statistics show that those with major depression are 20 time more likely to kill themselves. This is a strong selective penalty. Depression appears to reduce libido and tends to make one less attractive as a sexual partner. Depressed mothers also prove to be poorer carers of their off-spring. All of which seems to add up to an evolutionary disadvantage.
Despite some progress in research, Leif Kennair, associate professor of psychology at the Norwegian University of Science and Technology, says that not enough evolutionary psychologists are investigating mental illness, and not enough clinical psychologists “are working on developing procedures based on evolutionary understandings … and testing these out in clinical trials.” Much more such testing needs to be done, he says.

David Nettle, a psychology professor at the University of Newcastle in the UK argues that “modern day depression is a mismatch between human beings adapted for hunter-gatherer societies and the contemporary world.”

Let’s leave the last word to Nettle. Writing in the Journal of Affective Disorders Nettle says:

“There has been a recent surge of interest in the evolutionary basis of depression. One approach argues that the affective mechanisms that are dysregulated in depression are adaptations. Whilst a second approach argues that depression itself is an adaptation. Adaptations generally have four hallmarks; they lack heritable variation. Show evidence of good design, are evoked by appropriate triggers, and fitness is reduced where they are absent. Depression shows none of these hallmarks. It is characterized by heritability, recurrence, cognitive impairment, and poor social outcome. In an alternative evolutionary, I argue that evolution has produced a continuous population distribution of affective reactivity that is subject to stabilizing selection. This conceptualization, in which depression itself is not selected for, is compatible with the known clinical and epidemiological facts.”

{For those who want to read more, the above is a quotation from the Abstract of Nettle’s article “Evolutionary origins of depression; a review and reformulation” Journal of Affective Disorders 81 (2004) 91 – 102. This is a good summary of the various theories relating depression and evolutionary psychology.}

15 Replies to “Is Depression a Biological Adaptation?”

  1. Thanks Ted,

    This was a very interesting post.

    Given my own close experience with this type of thing, I have long pondered such questions as whether the incidence has truly increased, or just been increasingly diagnosed, or labelled.

    This month I’m participating in Movember as one way to help fund research into, and assistance in, the domain:



  2. It has had a lot of names over the years. Depression, shell shocked, traumatised, etc. Whether the incidence is increasing or not is probably impossible to tell. Even suicide rate increases I think are difficult to compare with rates 20 years ago let alone 200. Until recently we did not talk about such things openly and even now I suspect there is still a great deal hidden.

    Me personal view (gut feeling only) is that depression in Australia is increasing. I also think this is surprising as there is no real obvious catalyst for it. After the last world war increased depression rates were fairly predictable but why now? Some possibilities.

    We spend less time in the natural world. Kids watch TV and play video games rather than make believe games, riding bikes, and playing sport. The natural world does seem to sooth a troubled soul. I remember a Michael Leunig cartoon depicting a father and son watching a sun set together on TV while there was the same scene occurring out their window.

    Our brain is always stimulated. We watch TV, text a friend, have a conversation and eat dinner all at the same time and this we call down time!

    We have all of our physical needs met almost as a given (we don’t need to do anything). There is no real threat of starvation in this country. The calories that go into rubbish bins could feed tens of thousands if not millions. We now worry far more about having the latest I-something as opposed to our physical needs. Our ego has become all powerful in this environment and a threat to the ego seems just a traumatic as a threat to our physical self.

    All the media forms are paid for by consumer spending (advertising). Not just the ads but the shows themselves are designed specifically to make us buy selected products. Some of the shows (even dramas) are funded by product manufacturers. With this bombardment of professional marketing aimed at manipulating us it is not surprising to me that we have problems with self worth. The right car, the right clothes, TV, watch, sun glasses,….. all essential elements of happiness.

    As always I have no answers just some thoughts.

  3. Well, of course Greg, as usual you have hit the nail on the head. Depression, I am sure, has increased in the modern developed world. That it has done so is due to two particular issues. Firstly most of us have no idea about what makes us happy. (I have written a number of blogs on this that you might refer to for reflection.) Secondly the modern consumer society aided and abetted by the “Pop Psychologists” have led us to believe that we can be anything we want and have anything we want – and therefore our expectations about material well-being are unduly inflated. As a result we face the dual problem of believing we need status and material acquisitions to be happy and that if we don’t get what we want it is through personal failure. It is difficult to contend with the world when our mindset is so wrong.

    Contrast with this. Matthieu Ricard,tells the story of a man who was born without arms or legs. He lives on the outskirts of a village in a little bamboo hut of just a few square yards. He came from Tibet forty years ago, carried by fellow refugees. He has lived in this hut ever since. The mere fact that he is still alive is extraordinary in itself, but even more striking is the joy that radiates from him. Ricard reports “Every time I see him, he is in the same serene, simple, gentle and unaffected frame of mind. When we bring him small gifts of food, blankets, a portable radio, he says that there is no need to bring him anything. ‘What could I possibly need?’ he laughs.”

    Is there not a lesson for us there?

  4. Father Robin, love your “I’d like to be wise but I am just getting older” comment. Precisely how I feel. 🙂 So many questions so few answers.

  5. Father Ted.

    “Of course the most ubiquitous concern about the omnipotence of God seemed to have been first raised by Epicurus.

    Full Circle?

    Sorry, comments for this entry are closed at this time”


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