What did Harry Harlow’s research on rhesus monkeys prove? Monkeys are more fearful if they are removed from their mothers.

Monkeys need milk from their mothers more than warmth and comfort.

Monkeys are not fit to raise human children in isolation.

Monkeys are unaffected by separation from their mothers.

Even without complete isolation, the infant monkeys raised without mothers developed social deficits, showing reclusive tendencies and clinging to their cloth diapers. ... Harlow's work showed that infants also turned to inanimate surrogate mothers for comfort when they were faced with new and scary situations.