The biological 'function' of depression

In the west depression is one of the most common reasons for seeking help from a therapist or other healthcare professional. But depression is also widespread across the globe, affecting people from all cultural and social backgrounds—though it may often be conceived of, and named, differently in non-western cultures [1]. And so it’s long been reckoned that there must be good biological reasons for depression’s global ubiquity.

In evolutionary terms, depression is said to be ‘adaptive’, that is, it has some sort of biological purpose in order to enable us to function more effectively in the longer term, either as individuals or as part of a social group. The discussion has given rise to a number of contrasting hypotheses. Here are just two. 

Depression gives information to us and others

Let’s take the Social Navigation Hypothesis, or the SNH, first put forward some nine years ago by two biologists from the University of New Mexico [2]. Paul Watson and Paul Andrews have suggested that depression actually helps with problem-solving, especially problems relating to social situations.

One of the features of depression is ‘rumination’—the tendency to go over and over problems and negative experiences, dwelling on them to the exclusion of other thoughts. This can, they propose, be useful, as it sensitises the individual to information they can use to understand situations better. In therapy, the content of the ruminations can be discussed as part of an awareness raising process—but why are these ruminations dominating at this time? Are they helping the individual learn something?

In addition, the SNH proposes that depression can act as a motivator for the other people in a relationship with, or those sharing a social network with, the depressed person—the ‘cry for help’ signal of depression could ensure help emerges in response from partners and other contacts. This is not done in a conscious way of course—it’s not that the depression is an ‘act’ or a performance. But it does, say Watson and Andrews, give voice to feelings that indicate a need for social support.

Andrews went on to develop the notion of ‘depression as information’ with other colleagues. The theory posits that as human beings are analytical creatures, rumination is itself a form of analysis—repetitive and often not rewarding in itself, even so. The anhedonia (the technical term for the loss of pleasure in normally pleasurable experiences) that accompanies many depressive episodes is there precisely because it allows for more rumination—lack of pleasure means the brain is not ‘diverted’ by other distracting pleasures from its all-important analytical task.

Depression as a protector

A rather different hypothesis is the one put forward by psychologist Randolph Nesse, a researcher in evolutionary medicine at the University of Michigan [3]. 

Just as physical pain can be ‘normal’, alerting us to danger (such as the pain we feel with intense heat or intense cold), depression is a biological warning signal, too. A low mood stops us trying to chase after impossible goals—it tells us that now’s the time to ‘give up’ and move on to something else more achievable. Over millennia, this protective mechanism helped us identify activities or ventures we could not possibly achieve, and so permitted us to focus energy and resources on what we could do instead.

One reason for the high levels of depression in modern-day western settings is, according to this hypothesis, the pressure to succeed—the drive to achieve is not ‘healthy’ for many people, who can become at first mildly depressed, and then more chronically as they carry on ignoring the ‘warning signals’.

References

1. Reducing the global burden of depression: Population-level analysis of intervention cost-effectiveness in 14 world regions, by D. Chisholm

2. Toward a revised evolutionary adaptationist analysis of depression: the social navigation hypothesis, by Paul J Watson, Paul W Andrews

3. Is Depression an Adaptation? by R M Nesse

Image credits: Dan W Dooley, Wikimedia, Royal Ontario Museum