Mutant monkeys get hooked on a drug called mum

A gene mutation determines whether or not macaque infants make a fuss when their mothers are missing, say researchers. A similar mutation has been linked to alcoholism and drug abuse in humans.

The work could explain why some children are cry babies and some are more independent, says Christina Barr, a neuroscientist at the National Institute of Alcohol Abuse and Alcoholism in Bethesda, Maryland, US, who led the study.

"There are some kids that go with the flow and there are some that are very reluctant [to leave their mothers]," she says.

When infants and young animals spend time with their mothers, their bodies release natural drugs called opioids. Molecular receptors on brain cells sop up these chemicals and provide temporary feelings of pleasure.