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.}