EARLY BEHAVIORAL-DEVELOPMENT AND TEMPERAMENTAL TRAITS IN MOTHER-REARED VS PEER-REARED RHESUS-MONKEYS

Behavioral characteristics (''traits'') of 24 mother-reared and 24 nur sery/peer-reared rhesus monkey infants were assessed via rating scales from the third through the seventh month of life while housed with th eir rearing partners, and from months 8-10 after all animals had been placed in novel peer groups. The animals were also tested at 8 months of age on the Bayley Scales of Infant Development adapted for nonhuman primates. During the early period effects noted were primarily develo pmental. Peer-reared animals were rated as increasingly less cautious and more attentive to the outside environment over time, while mother- reared infants declined in ratings of dependence on their mothers. All animals were rated as increasingly active and excitable, and less fea rful, over time. For the period of months 8-10, peer-reared animals sh owed higher confidence ratings in month 10, and all animals showed a d ecline in attachment to cagemates. Mother-reared animals showed more h ostility to the examiner during Bayley testing, whereas peer-reared an imals showed more fear. Sex effects included greater ratings for indep endence from mothers, greater activity over both the early and later p eriods, greater excitability, greater attentiveness to the extra-cage environment, less cautiousness, and better performance on one Bayley p roblem for females.