Clinical Depression in the Context of Human Evolution

If evolution ensures survival of the most adaptable species, how did it not vanquish mental depression in humans? This question has been on my mind for several years, and it is time to examine it in the context of a new hypothesis proposed by two scientists.

Background

Between 30 to 50% people suffer from a major depressive episode in their lifetime. It is generally considered to be a disease of the brain, an illness that needs treatment. In the millions of years of human evolution, natural selection was at work, ensuring that the ones among us who were best at surviving, adapting, and reproducing, carried the human species forward. Mental depression reduces ones ability to survive, adapt, and reproduce. It would then be reasonable to expect that those humans afflicted with this disease would have become extinct by now. The genes responsible for, or conducive to depression, should have eroded out of the thriving gene pool. But that, as we know, is far from the truth.

While animals are also known to experience depression, it is still an emerging field of research, and I am skeptic whether their sadness is just a rational response to external circumstances or is full-blown causeless depression like in humans.

Meredith Small, an anthropologist at Cornell wrote last year:

The capacity to feel presumably helps us solve problems and survive, and is essential for group living, and perhaps inconsolable depression is simply emotional baggage that tags along with the good stuff. Or maybe unhappiness and a tendency towards suicide is the product of the uncontrolled nature of our quicksilver minds. We think a lot, and our wondering minds are just as likely to think sad as happy.

LiveScience quotes Meredith in Why Did Evolution Produce Depression, along with Paul Andrews and J. Anderson Thomson, Jr., who have argued in Scientific American that “depression is in fact an adaptation, a state of mind which brings real costs, but also brings real benefits.”

The Hypotheses

The two scientists have published their views in a Scientific American article “Depression’s Evolutionary Roots”. The key points:

  1. Depression should not be thought of as a disorder at all. They argue that depression is in fact an adaptation, a state of mind which brings real costs, but also brings real benefits.
  2. One reason to suspect that depression is an adaptation, not a malfunction, comes from research into a molecule in the brain known as the 5HT1A receptor….The ability to “turn on” depression would seem to be important, not an accident.
  3. Depressed people often think intensely about their problems. These thoughts are analytical and persistent. Depressed people have difficulty thinking about anything else. This analytical style of thought, of course, can be very productive and can help you solve the problem causing the depression.
  4. Analysis requires a lot of uninterrupted thought, and depression coordinates many changes in the body to help people analyze their problems without getting distracted.
  5. Symptoms of depression make sense in light of the idea that analysis must be uninterrupted. The desire for social isolation helps the depressed person avoid situations that would require thinking about other things. Inability to derive pleasure from sex or other activities prevents the depressed person from engaging in activities that could distract him or her from the problem. Even the loss of appetite could be viewed as promoting analysis because chewing and other oral activity interferes with the brain’s ability to process information.
  6. If depressive rumination were harmful, then bouts of depression should be slower to resolve when people are given interventions that encourage rumination, such as having them write about their strongest thoughts and feelings. However, the opposite appears to be true. Several studies have found that expressive writing promotes quicker resolution of depression, and they suggest that this is because depressed people gain insight into their problems.
  7. There is another suggestive line of evidence. Various studies have found that people in depressed mood states are better at solving social dilemmas.
  8. Depression is nature’s way of telling you that you’ve got complex social problems that the mind is intent on solving. Therapies should try to encourage depressive rumination rather than try to stop it, and they should focus on trying to help people solve the problems that trigger their bouts of depression.

Critique of An Unquiet Mind

  1. The semantic difference between “disorder” and “adaptation” has huge ramifications and consequences in how society treats depressed people. These gentlemen have perhaps not thought through these ramifications. By their own account, they describe the unhealthy, self-destructive, treatment-worthy behavior of people in this state of mind, so what goals do we achieve by terming them an adaptation rather than an illness, disease, or disorder?
  2. I am not sure if this is “missing the wood for the trees”. Humanity would benefit greatly if scientists studying the brain and depression focus on their excellence at dealing with trees and not try to paint the woods.
  3. Analytical and persistent thinking in depression is usually in the form of obsession and brooding – two words, often associated with depression, conspicuously missing in the article. The obsessive nature of thinking in depression is rarely productive, and often self-destructive.
  4. Dealing with lack of distraction in the next point, here I would like to point out the conspicuous absence of the discussion of anxiety in the article. Most forms of depression are closely associated with anxiety, and there is no discussion of whether anxiety also contributes to “productive analytical thinking”.
  5. Uninterrupted “analysis” often leads to suicide. Not eating leads to serious physical harm. Substance abuse is also a serious problem with those afflicted with the illness of depression. The idea that suicide, starvation, and substance abuse “can be viewed as promoting analysis” is not just ridiculous, but very insensitive. The brains ability to process information is not enhanced by any of these activities.
  6. The studies confirm that emotional expression is an important healing factor in depression. It is not just the writing, but the family, friends, consultation and therapy that follows it, which is often crucial for resolving issues.
  7. The first study is of whether mood influences level of cooperation in people and had just two experiments. The second examines how family relationships are relevant to adolescent depression. The notion that people with depression are better at solving social dilemmas is again, preposterous and highly insensitive.
  8. Many forms of human depression have no cause in the external world. It is not a rational response to an external social problem. It is often causeless and intrinsic or inborn. The scientists view of depression seems to be very narrow minded.

Conclusion

It is clear that we do not have any definite answer yet. Though Depression has been studied in all cultures, we do not know if it existed in early stages of evolution. If it didn’t, and we find that it has developed in recent history (in evolutionary terms), I’m sure natural selection will eventually eliminate it.

Meanwhile, it does not behoove Scientific American to publish such articles. If you want to learn about mental depression, here is the best place to start.

SaltedLithium

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  • I had also read about this theory and had in fact bookmarked that article as I found it very interesting. The subject of evolution and genetics fascinates me. But ofcourse we do not have all the answers as yet although research in this field seems to be growing by leaps and bounds.
    I think this new theory does have some basis. After all a lot of people who are geniuses are also a little mentally disturbed. I can think of many poets and writers who did in fact commit suicide. I don’t the complete answer, but as you mentioned, a lot more work needs to be done in this area.

  • Hi Nita, thanks for the comment. Yes, it is a fascinating subject, and I was disappointed with this particular hypothesis.

    There is some basis for adaptive theories of depression, but I need to investigate and study them further. With this post, I wanted to “break in” on this topic. 🙂

  • Thank you for your humane analysis of the so-called benefits of depression. When someone is suffering our job as fellow human beings is to help them.
    Richard Zwolinski
    LMHC, CASAC