The Nature of Love (American Psychologist article)

Harlow argues that contact comfort—the soft, warm, tactile qualities of a caregiver—is the overwhelming variable in the development of an infant primate’s affectional response to its mother. The paper rejects the behaviorist and psychoanalytic “cupboard love” premise that attachment forms because the mother reduces hunger. In Harlow’s dual-surrogate experiments, infant rhesus monkeys fed by a wire mother still spent most of their time clinging to a non-feeding cloth mother, returning to the wire surrogate only to eat. The finding made love a legitimate object of experimental inquiry rather than a sentimental topic beneath scientific attention.

Harlow built two surrogate mothers: a wire-mesh frame that could dispense milk, and a similar frame covered in soft terry cloth that provided warmth but no food. Infant monkeys were placed in cages with both surrogates, with feeding conditions varied so that sometimes the cloth mother lactated and sometimes the wire mother did. Time spent on each surrogate was recorded automatically over 165 consecutive days. Across conditions, the infants overwhelmingly preferred the cloth mother, even when she provided no milk, and their responsiveness to the wire mother decreased with age. The design directly pitted tactile comfort against nutritional reward and found the former decisively more powerful.

Harlow and Bowlby were developing converging critiques of the same orthodoxy, though from different directions. Bowlby, working in Britain, drew on ethology and clinical observation to argue that attachment is a primary, biologically based bond rather than a derived drive. Harlow’s contribution was experimental and, in the American context, strategically decisive: his hard-science demonstrations gave Bowlby’s more theoretical claims empirical weight against behaviorist skepticism. Deborah Blum’s biography of Harlow notes that Bowlby’s campaign was seen by many psychologists as “soft, sentimental and unscientific” until Harlow’s monkey data broke the barriers of doubt. The two bodies of work together established attachment as a central construct in developmental psychology.

The 1958 paper established contact comfort as crucial for normal affectional development; Harlow’s subsequent work asked what happens when that comfort is absent entirely. Monkeys raised in total social isolation for three, six, or twelve months showed progressively severe disturbances: self-clutching, self-biting, rocking, and an inability to interact with peers when reintroduced. Females isolated for twelve months, when later impregnated, often became abusive or neglectful mothers. These studies extended the contact-comfort thesis by demonstrating that deprivation of early social and tactile experience produces enduring psychopathology, not merely transient distress. They also darkened Harlow’s public reputation and became central to the animal rights critique of his work.

The paper’s core finding—that contact comfort matters enormously and that feeding alone does not explain attachment—has held up robustly and became foundational for attachment theory and developmental psychology. However, later researchers have qualified Harlow’s implicit claims about the sufficiency of contact. Harry Harlow’s colleague and biographer Deborah Blum notes that his own later work revealed that monkeys raised with only a cloth surrogate still showed social deficits; contact comfort was necessary but not sufficient for normal development. Comparative psychologists also caution that rhesus monkey findings cannot be directly generalized to humans without accounting for species differences. The ethical controversy surrounding Harlow’s methods, particularly the isolation experiments, has increasingly framed how the work is taught and remembered.