The Functions of Postpartum Depression

Introduction

Mothers with postpartum depression (PPD) commonly have thoughts of harming their
children, exhibit fewer positive emotions and more negative emotions towards 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; Beck,
1996b; Cohn, Campbell, Matias & Hopkins, 1990; Cohn, Campbell & Ross, 1991; Field & et
al., 1985; Fowles, 1996; Hoffman & Drotar, 1991; Jennings, Ross, Popper & Elmore, in press;
Murray, 1991; Murray & Cooper, 1996). Although most researchers view PPD as a disorder,
evolutionary theorists frequently have argued that there are circumstances when it would in the
mother’s fitness interest to reduce or eliminate her investment in her offspring, for example,
when there is insufficient social support to raise the infant, or when the infant has low viability
(Clutton-Brock, 1991; Daly & Wilson, 1984; Daly & Wilson, 1988; Hrdy, 1979; Hrdy, 1992;
Trivers, 1974).

PPD is a depressive episode with onset occurring one month postpartum (APA, 1994).¹
Depressive episodes are characterized by a number of symptoms including depressed or sad
affect, marked loss of interest in virtually all activities, significant weight loss or gain, insomnia
or hypersomnia, psychomotor agitation or retardation, fatigue or loss of energy, feelings of
worthlessness or guilt, diminished ability to think or concentrate, and recurrent thoughts of
death (APA, 1994). A diagnosis of a DSM IV major depressive episode requires that five of
these symptoms be present during a two-week period, and that at least one of the symptoms is
either depressed or sad mood, or a markedly diminished interest or pleasure in all or almost all
activities.

Three correlates of PPD are consistently found by researchers: marriage problems and lack
of social support, particularly the father’s (table 1), infant problems, including pregnancy and
delivery problems (table 2), and a prior history of depression or other emotional problems
(Atkinson & Rickel, 1984; Cutrona & Troutman, 1986; Gotlib et al., 1991; Graff, Dyck &
Schallow, 1991; Logsdon, McBride & Birkimer, 1994; O’Hara et al., 1984; O’Hara, Rehm &
Campbell, 1983; Whiffen, 1988; Whiffen & Gotlib, 1993). This paper will propose three related
adaptive functions for PPD that are consistent with the expectations of evolutionary theorists and
the first two correlates noted above. First, negative affect—i.e., sad or depressed mood—should
be associated with social circumstances that were reproductively costly in ancestral
environments (e.g., lack of social support or infant problems). This “psychological pain”
hypothesis (Alexander, 1986; Nesse, 1991; Nesse & Williams, 1995; Thornhill & Thornhill,
1990; Thornhill & Thornhill, 1989; Tooby & Cosmides, 1990) is strongly supported by existing
evidence. Second, mothers will take actions to reduce their levels of psychological pain, thereby
reducing their reproductive costs. This hypothesis is also well supported by existing evidence.

Study

Emotional Support:

Affonso and Arizmendi 1986

¹The 1-month criterion established by the American Psychiatric Association is obviously somewhat arbitrary and
is meant to distinguish PPD from the far more common, less severe, and transitory blues experienced by two
thirds of all mothers in the first 1 to 2 weeks postpartum. The relationship between PPD and the blues is not clear.
PPD is also distinguished from postpartum psychosis, a rare and extreme set of symptoms involving delusions and
hallucinations.

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