Therapy of isolate Rhesus: different partners and social behavior

36 monkeys from 3 different rearing conditions were subdivided into 3 groups and then paired daily for 20 weeks either with others that were (a) socially sophisticated 9-month-old monkeys; (b) partial isolates, reared alone from birth for 9 months; or (c) socially naive 3-month-old infant monkeys. When 12 9-month-old partial isolates were thus split and tested, social play was greater in isolates paired with sophisticated therapists and least in isolates paired with isolate therapists. Fear showed the reverse pattern. Hostility was greatest in those infants, isolates, and sophisticates when paired with isolates and least in all groups when paired with infants. Of the nonisolate groups the infants were affected by their pairing the most, showing reduced social play when paired with the isolates, but increasing play when with sophisticates. Evidence is found against a learning or instrumental model of aggression production, and a novel theory is advanced suggesting that infants are genetically predisposed to acquire specific behavioral characteristics shown by the mother.