Postnatal Depression – An Evolutionary Mechanism?

Postnatal Depression is an awful experience, I know, I’ve had it.  I experienced it with my son, and I could hypothesize a lot about the various causes, antecedents and factors that contributed to my presentation of it, but I’m not going to here.  What I am going to do is discuss a theory which I explored within a University paper I undertook last year, that PND is perhaps, an evolutionary adaptation.  I appreciate that this is largely theoretical, but to me it explains a lot, so bear with me.

Postnatal depression can be defined (loosely, I don’t see this as being prescriptive) as a depressive disorder that generally occurs within 4 weeks of baby being born and can occur up to three months post birth (Cuijpers 2008).   It is estimated that PND affects approximately 15% of all births in the postpartum period (Pearlstein 2009).   In a review of literature undertaken for a meta analysis of psychological treatments of PND, Cuijpers found that PND has been positively correlated with a wide range of negative outcomes, including marital stress and divorce, increased risk of abuse and neglect, maternal suicide, infanticide, attachment insecurity and an extensive range of increased risk of cognitive, behavioral and emotional problems in the infant and indeed, adult child of the depressed mother.   In reviewing literature surrounding parental depression and the effects on children, Cichetti (1999) found that many depressed women had also experienced “negative caregiving” which would suggest that an incidence of PPD could have a generational effect.   Such generational effects would (quite obviously) have high community social and financial costs.
Woman with PND

Evolutionary theory suggests that there has to be some sort of “purpose” to all aspects of our personality, that they all have an evolutionary basis, some reason to help us survive and thrive in order to have been made a part of us  (Cervone & Pervin 2010).  Trivers (1972) hypothesized that much of our behaviours around sex and reproduction is related to what he calls the “Parental Investment Theory”.  Parental investment theory is the concept that the amount of time any parent puts into raising their offspring is often done at the cost to their own wellbeing, largely for genetic gain, the continuing of your lineage.  Women “invest” more in reproduction than men do, therefore this affects our behaviour, our personalities and the way we view the world.  As women, we, effectively, put more up, when we get pregnant, than does a man who gets us pregnant.  We gestate for around nine months, we lactate for years afterwards (remember we are talking about pre-formula days) and we have to look after a dependent child for years.  This is partly because, a woman can be sure that the child is hers, a man (lets face it) has no such sense of surety and therefore not only has less to lose/invest, but can be less sure that the return on his minimal investment is truly his.  Now please note, I’m not bashing men here, I’m merely reducing this down to it’s basics, to an evolutionary view.

At first it can be difficult to see why PND would have an evolutionary basis.  Why would a woman get depressed enough to, potentially reject her young, or even, in the worst case scenarios, commit infanticide?  Afterall, shouldn’t she have an investment in seeing her genetic line continue?   However when we examine it through the Parental Investment Theory we can hypothesize that it’s a reaction to a potential cost to the mother “which motivates her to evaluate whether to continue or cease to provide care to her offspring” (Tracy 2005).  Tracy states that evolutionary theory suggests that psychological pain is an indication that the individual has suffered or is suffering from a social cost or injury.  He asserts that PND is a sign to the woman that the cost of raising that child is potentially not worth the gain and so PND becomes a way to help the woman switch off.   The cost of raising a child can seem higher to the woman if there is a perceived lack of support from her partner, paucity of effective social networks, if there is a complicated birth or health problems for mother or infant, or if there is a lack of resource with which to provide for the child.  Tracy further claims as proof the fact that many other studies point to these being significantly high risk factors in the onset of PND.

For an evolutionary theory to have validity it needs to be a human universal and thus be seen cross-culturally (Cervone & Pervin 2010).  Tracy maintains, through review of research, that PND is found cross culturally, which would support his theory that PND is an evolutionarily evolved defense mechanism to guard against extreme cost to the woman.

How can we see this in the here and now?  Well, given that many families, many women, give birth devoid of community, devoid of support, it’s not too great a leap to see how a woman could feel a complete lack of support, she could feel this in a deep part of her, a part where she feels alone in this new and foreign land of babyhood.  Such a lack of community support could well “switch on” that evolutionary mechanism, that would enable her to “detach” from the baby purely because she recognises, at some deep level that to continue to care for the child would be to her detriment.  So, she, quite literally switches off. She becomes depressed.

Even *if* she is actually surrounded by family, that may not actually translate into the sort of support that she feels she needs.  The support must be, at least to the woman, a deeply personal thing.

So if we are seeing a lot of postnatal depression, then surely that’s an indication that women might be, in a deeply survivalist sense, feeling unsupported in our communities?   This should be a clarion call to action.  If this theory is true, if PND is an evolutionarily developed mechanism, and if we are seeing it, supposedly in a time of plenty, then maybe we need to rebuild the support structures around women, around mothers.

Oddly, I don’t even need to think about evolutionary theory to think that’s true.  I don’t think that we support new mothers very well in our societies.  I don’t think our communities are set up to support new mothers at all.  And I think that this is seen in rates of postnatal depression, and if we do hold to the evolutionary theory of postnatal depression, then this should be a wakeup call, that women, in a very primal way, are saying loud and clear, that our society is sick, and they are the canaries in the mine.

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Cervone, D., & Pervin, L., (2010).  Personality : theory and research.  (11th ed.). Hoboken, NJ. : Wiley

Cichetti, D., Toth, S., & Rogosch, F., (2006).  The Efficacy of Toddler–Parent Psychotherapy to Reorganize Attachment in the Young Offspring of Mothers With Major Depressive Disorder: A Randomized Preventive Trial.   Journal of Consulting and Clinical Psychology, 74(6), 1006-1016.

Cuijpers, P., Brannmark, J.G. & van Straten, A. (2008).  Psychological treatment of postpartum depression: a meta-analysis. Journal of Clinical Psychology, 64(1), 103-118.

Pearlstein, T., Howard, M., Salisbury, A., & Zlotnick, C. (2009). Postpartum Depression.  American Journal of Obstetrics and Gynecology, 200(4), 357-364.

Tracy, M. (2005). Post-Partum Depression an Evolutionary Perspective. Nebraska Anthropologist, Paper 12. http://digitalcommons.unl.edu/nebanthro/12

Trivers,R. (1972). Parental Investment and Sexual Selection.  In Campbell, B. G. (Ed.), Sexual Selection and the Descent of Man 1871-1971 (pp 136-179). Chicago, United States: Aldine.

One Response to Postnatal Depression – An Evolutionary Mechanism?

  1. I work with pre and post natal moms and what I have observed is that many of those who are suffering from ante-natal depression are living in circumstances (environments) where they were struggling with difficult situations, or were depressed before they got pregnant. the pregnancy complicated their lives further-and yes a lot of it is circumstances and lack of support.

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