Wildlife rehabilitation of most species is done with minimal human contact or "habituation," and takes weeks or, at most, months. But that's not possible with primates. The famous experiments that psychologist Harry Harlow conducted in the 1950s on maternal deprivation in rhesus monkeys were landmarks in both primatology and the evolving science of human attachment.
“Harlow’s most famous experiment involved giving young rhesus monkeys a choice between two different ‘mothers.’ One was made of soft terrycloth, but provided no food. The other was made of wire, but provided food from an attached baby bottle. Harlow removed young monkeys from their natural mothers a few hours after birth and left them to be ‘raised’ by these mother surrogates. The experiment demonstrated that the baby monkeys spent significantly more time with their cloth mother than with their wire mother.
I love being a surrogate monkey mom, but I can't wait to be a non-surrogate monkey grandmother.