Biobehavioral comparisons between adopted and nonadopted rhesus monkey infants.

Differences between adopted and nonadopted infant rhesus monkeys were examined, as were differences between biological and foster mothers, in measures of infancy and postinfancy behaviors, maternal-infant interactions, and neuroendocrine and behavioral responses to separations. Newborns were experimentally allocated to continuous postnatal care by either their biological mothers (n = 9) or adoptive, nonbiological mothers (n = 7). Behavioral observations were completed during the neonatal period, during separations at 30 days and 5 months, and from 6 to 18 months of age, when animals were housed in a large social group. Maternal and infant responses to separation stress were assessed using measures of behavioral, adrenocortical, and growth hormone reactivity. Out of 84 possible comparisons, only six achieved statistical significance, a number compatible with the operation of chance. Negligible differences in behavioral and neuroendocrine endpoints were found between adopted and nonadopted mother-infant pairs. These findings lend additional credence to human studies finding no increase in the incidence or severity of mental disorders in adopted children.