Attachment in Rhesus Monkeys
STEPHEN J. SUOMI
Attachment is not an exclusively human phenomenon. Although the theory that John Bowlby conceived and developed during the 1950s and 1960s reflected his clinical observations of infants and young children (even in the face of his psychoanalytic training), it also had a strong basis in his knowledge of (and near-constant interest in) ethological studies of developmental phenomena in animals, especially nonhuman primates. Indeed, it can be argued that Bowlby (1969/1982) tailored several essential features of his attachment theory specifically to account for clear-cut commonalities in the strong behavioral and emotional ties that infants inevitably develop with their mothers—not only across all of humanity, but also among our closest evolutionary relatives.
At about the time that Bowlby published, with James Robertson, his seminal studies of infant separation via hospitalization (Robertson & Bowlby, 1952), he became aware of the classic ethological studies of filial imprinting in precocial birds. During this period, he developed a close friendship with Robert Hinde, a worldclass ethologist at Cambridge University, who was in the process of shifting his own basic research interests from song-learning in birds to mother–infant interactions in rhesus monkeys. Hinde soon had rhesus monkey mothers raising babies in small captive social groups (e.g., Hinde, Rowell, & Spencer-Booth, 1964), and Bowlby came to recognize patterns of behavior shown by the infant monkeys toward their mothers—but not toward other adult females in the group—that strikingly resembled recurrent response patterns of human infants and young children he had observed over years of clinical practice. These common patterns provided Bowlby with powerful evidence supporting his assumption that attachment has its basis in biology.
Indeed, virtually all of the basic features of human infant behavior that Bowlby’s attachment theory specifically ascribed to our evolutionary history could be observed in the normative mother-directed behaviors of rhesus monkey infants described by Hinde and other primate researchers. For Bowlby (1958, 1969/1982), the fact that rhesus monkey infants and human babies share unique physical features, behavioral propensities, and emotional labilities linked to highly specific circumstances was consistent with the view that they also share significant parts of their respective evolutionary histories. He argued that these features, present in newborns of each species but often largely absent (or at least mostly hidden) in older individuals, represent successful adaptations to selective pressures over millions of years. To Bowlby, those characteristics common to human and monkey infants reflect evolutionary success stories and should be viewed as beneficial, if not essential, for survival of both the individual infant and the species.
What are those common characteristics—and