Psychobiological Origins of Infant
Attachment and Separation Responses
H. JONATHAN POLAN
MYRON A. HOFER
John Bowlby’s great achievement was to place filial attachment firmly within the small group of behavioral systems that have been most essential for the survival of humans and many other species of mammals during evolution. By showing how attachment may be regarded as a motivational system in its own right, on a par with sex and appetite, he cut through a longstanding debate on the origin of the child’s tie with the mother. But in so doing he left open the early developmental processes leading to the formation of attachment. Although Bowlby hypothesized that in slowly developing (altricial) mammals such as rats, dogs, and primates, processes analogous to “imprinting” (as in rapidly developing birds and sheep) occurred, the actual processes involved in acquisition of the intense and specific behaviors that keep such infants close to their mothers remained unknown. Because Bowlby (1973) and other, more recent theorists explain the infant’s complex responses to separation in terms of this attachment behavior, our understanding of separation also rests on an uncertain foundation. Research on attachment, at least in humans, has moved on to the developmental role and generational transmission of qualitatively different patterns of attendant behavior (Main, 1996), as if the basic nature of and the processes underlying attachment and separation were settled.
Since the essential phenomena of infant attachment—maternally directed proximity seeking and the response to maternal separation— occur in most mammals studied thus far, they appear to be strongly conserved in evolution; that is, the basic underlying mechanisms (from genes to neurobehavioral systems) are likely to be similar in all mammals. And studies in the last two decades have strongly supported this inference. Reviews have appeared that summarize research on attachment across a number of mammalian species (Kraemer, 1992; Leon, 1992), so we are not taking that approach here. Instead, we think that more can be gained from an indepth analysis and interpretation of recent research on a single species. In the last two decades, we have learned more about the psychobiological processes underlying the parent–infant relationship in the rat than in any other species. The multiple analytic experiments on which this knowledge is based require a rapidly developing, inexpensive, easily accessible, laboratoryadapted animal and are thus not suited to primate species, especially humans. Naturally, studies on rats cannot settle questions about human development. But they can suggest new ways to interpret human behavior, new ideas about what to look for, and new hypotheses about underlying biological processes. Above all, they can give us a comparative perspective and suggest how attachment in humans evolved.
In this chapter we review what is known about the biological and psychological processes underlying the development of behavioral responses characteristic of attachment in the young rat.