Postpartum depression

After giving birth, about 70-80% of women experience an episode of baby blues, feelings of depression, anger, anxiety and guilt lasting for several days. About 10% of new mothers develop the more severe postpartum depression (also postnatal depression), a form of major depression for which treatment is widely recommended.

An evolutionary psychological hypothesis for postpartum depression

Summary: Mothers with inadequate social support, an unhealthy child, a lack of resources (e.g., financial problems in contemporary societies), or other costly and stressful circumstances, have negative reactions towards the baby because these mothers would not have been able to successfully raise the child in ancestral-type conditions.

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Evolutionary approaches to parental care (e.g., Trivers 1972) suggest that parents (human and non-human) will not automatically invest in all offspring, and will reduce or eliminate investment in their offspring when the costs outweigh the benefits. Reduced care, abandonment, and killing of offspring have been documented in a wide range of species. In many bird species, for example, both pre- and post-hatching abandonment of broods is common (e.g., Ackerman et al. 2003; Cezilly 1993; Gendron and Clark 2000).

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Human infants require an extraordinary degree of parental care. Lack of support from fathers and/or other family member will increase the costs born by mothers, whereas infant health problems will reduce the evolutionary benefits to be gained. If ancestral mothers did not receive enough support from fathers or other family members, they may not have been able to "afford" raising the new infant without harming any existing children, or damaging their own health (nursing depletes mothers' nutritional stores, placing the health of poorly nourished women in jeopardy).

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For mothers suffering inadequate social support or other costly and stressful circumstances, negative emotions directed towards a new infant could serve an important evolved function by causing the mother to reduce her investment in the infant, thereby reducing her costs.

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Numerous studies support the correlation between postpartum depression and lack of social support or other childcare stressors. Mothers with postpartum depression also reduce their investment in their new offspring. They commonly have thoughts of harming their children, exhibit fewer positive emotions and more negative emotions toward them, are less responsive and less sensitive to infant cues, less emotionally available, have a less successful maternal role attainment, and have infants that are less securely attached (Beck 1995, 1996b; Cohn et al. 1990, 1991; Field et al. 1985; Fowles 1996; Hoffman and Drotar 1991; Jennings et al. 1999; Murray 1991; Murray and Cooper 1996). In other words, most mothers with PPD are suffering some kind of cost, like inadequate social support, and consequently are mothering less. PPD may be an adaptation that, via negative emotions, informs mothers that they cannot "afford" the new baby and that motivates them to reduce or eliminate investment in offspring. It may also help them negotiate greater levels of investment from others.

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If this view is correct (and it is far from proven), mothers with PPD do not have a mental illness, they need more social support, more resources, etc. Treatment for PPD should therefore focus on helping mothers get what they need. For more on this hypothesis, see Hagen 1999 and Hagen and Barrett, n.d..

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