The Functions of Postpartum Depression

mating effort, then parents need to decide, based on current circumstances, whether it is more
advantageous to invest finite resources in offspring, mates, or themselves. Investment in new
offspring should not be automatic.

A number of straightforward predictions follow from PI theory, two of which will be the
focus of this paper. First, when offspring require significant investment from mothers, mothers
should assess offspring viability (e.g., health) before providing the investment. Second, when
offspring require significant investment from both fathers and mothers in order to survive to
reproductive age, mothers should assess the availability of father investment before investing
themselves.

There is a correspondence between these two predictions of PI theory, and two widely
replicated correlates of postpartum depression, namely the mother’s perception of lack of
support from the father, and “infant problems,” including pregnancy and delivery problems
(tables 1 and 2). While PI theory makes it clear why a mother who has an infant with problems
or who is receiving insufficient social support will neglect, abandon, or kill her offspring, it
does not make clear why these circumstances lead a mother to experience depression. The
answer may lie in the link between adaptive problems and consequent adaptive behavior, that
is, it may lie in the evolved psychology of the mother.

Evolutionary psychology

The functional properties of organisms are called adaptations, and the terms function and
adaptation will be used interchangeably in this paper. Briefly, adaptations evolved because
they solved the recurring problems of survival and reproduction discussed in the previous
section. Hearts, lungs, and eyes are typical examples of adaptations, and each evolved to solve
an important problem: hearts circulate nutrients to other tissues in the body, lungs extract
oxygen from the atmosphere, and eyes collect visual information from the environment. These
organs are recognized as adaptations because the features of each correspond closely to the
problems they were intended to solve. This correspondence is called evidence of design. The
chambers and dense muscles of the heart are ideally designed for pumping blood, but poorly
designed for absorbing large quantities of gaseous oxygen. The numerous cavities of delicate
tissue that comprise the lungs are ideally designed for absorbing oxygen, but completely
ineffectual for focusing light. In order to solve the many problems involved in reproduction,
many adaptations are needed. Any organism can be therefore be viewed as a large but finite set
of functional components, or adaptations, each of which designed by natural selection to solve a
particular reproductive problem in ancestral environments.

The brain, like the rest of the body, consists of a number of adaptations, with vision,
hearing, smell, motor control, and physical pain being obvious examples. Evolutionary
psychology is the subfield of evolutionary biology that is attempting to identify the functional
components of the brain, often referred to as psychological adaptations (Barkow, Cosmides &
Tooby, 1992; Daly & Wilson, 1983; Daly & Wilson, 1984; Symons, 1979). Like other
adaptations, a psychological adaptation can be recognized by evidence of its having been
designed by natural selection to solve a particular reproductive problem. For example, physical
pain functions to inform an animal that its tissue is being damaged, provides information on the
precise location of the damage, motivates the animal to withdraw from the damage-causing
circumstances, and conditions the animal to avoid similar circumstances in the future. Each of
these capabilities requires a sophisticated organization of the nervous system, and each would
have facilitated reproduction of the organism.

In general, psychological adaptations evolved to extract information from the environment
that was relevant to reproductive problems, and to then generate behaviors, that, on average,

<<   4   5   6   7   8   9   10   >>

More intriguing information