Formation and expression of filial attachment in rhesus monkeys raised with living and inanimate mother substitutes.

The formation and expression of filial attachment was investigated in rhesus monkeys raised with dogs or inanimate mother substitutes in a longitudinal study spanning the first 4 years of life. At 2 months monkeys were identified within each rearing group as strongly attached or weakly attached, as measured by proximity, contact and clinging to the mother substitute in the living cage and in a novel room, and by differences in levels of distress vocalization and heart rate when they were alone and in the presence of the substitute mother in a novel room. By 4 months, all monkeys were attached, and the strongly attached and weakly attached monkeys of the first age-period were no longer distinguishable on any measure. The attachment was specific to the substitute mother. It was not exclusive, however, inasmuch as similar responses were elicited by a stranger of the same type as the substitute mother, although the stranger was less effective. The attachment figure was also influential when it could be seen but not touched. Evidence of attachment to the substitute mothers persisted until the end of testing at 44 months. Comparison of rearing groups support the hypothesis that the principal effect of living and inanimate mother substitutes is on responsiveness, rather than on the attachment process per se.