Alloparental care and wandering baby monkeys
Pierre Jacob recently discussed Sarah Hrdy's book Mothers and Others in which she argues that humans, like New World monkeys but unlike other apes, are cooperative breeders. As Pierre summarizes, cooperative breeding implies that newborns and youngsters have evolved the capacity to engage adults in caring for them and that adults have evolved the capacity to share the care of their offspring. Adults are therefore naturally attracted toward newborns, who eventually solicit their attention, and inexperienced mothers compete for newborns with other adults, including the mother, to gain more experience in parental care. The following video, just filmed by Mark Bowler at the Living Links Center in Edinburgh (where I am now pursuing my research) nicely illustrates Hrdy's description of alloparental care.
New born capuchin monkeys interacting with alloparents.
Notice the sequence when the newborn (Inti, a 2 months old male) climbs onto the back of another female (Santi): he is first sitting on his mother's back and looks into the face of Santi before climbing on her back. Although he is still very young and clumsy, he is willing to leave his mother for another individual. This might seem surprising, but Santi is a childless female who spends a lot of time sitting next to Inti's mother, Sylvie, and engaging Inti in various interactions (lipsmacking, grooming, etc). Worth pointing out is the fact that Santi and Sylvie are sisters.
Hrdy's hypothesis goes further as she proposes that, in humans, alloparental care is the evolutionary precursor of mind reading capacities. This more controversial hypothesis could gain further support if cooperative breeding species of monkeys showed more developed capacities for mind reading capacities than non-human apes. To my knowledge, mind reading capacities in monkeys have not been thoroughly tested, maybe because until now there has been no reason to suspect that monkeys would do better than non-human apes in these tasks (if you have relevant references, please share them by adding a comment). Hrdy's hypothesis could therefore foster the development of new experiments to test the mind reading capacities of new world monkeys, with the prospect of surprising results.