in their laboratory at the university of munich, the two psychologists joscha kÄrtner and manfred holodynskiare observing smiling and laughter in babies. does it emerge inevitably as soon as the brain is adequately developed, at about two months? the researchers suspect that's not the case. they've found evidence by observing the development of infants in other societies -- for instance, here in cameroon. for more than ten years colleagues of the researchers have been visiting the nso people in rural cameroon. their video footage shows that children here are treated very differently from those in western societies. mothers always carry their babies close to their bodies, even when doing housework. moments of face-to-face contact are usually the exception. and even when the mothers play intensively with their babies, the babies simply don't smile. why is that? the behaviour of parents evidently plays a larger role than brain development. >> people there don't attach such importance to making a baby smile. they do it because they think it's good for the child's health or strengthens it. but th