Every parent knows it, of course. And probably most of the rest of the population too, come to think of it.

But now an absolutely fascinating study could well give us some scientific insights into just why it is that peer pressure among youngsters - especially friends - seems so much more potent than the parental kind.

Dr Bridget Waller and PhD student Jerome Micheletta, of the University of Portsmouth's Department of Psychology, have been intensively studying a group of macaque monkeys at Marwell Wildlife in Hampshire, an animal park in which the animals are kept in conditions that closely resemble those they'd inhabit in the wild.

The researchers were interested in social signals and particularly in gaze-following, where animals start to gaze at something that another animal has already locked on to with its eyes. Because at any one time there will be many pairs of eyes in a monkey troop scanning the surroundings for information about food, threats, and sex, this gaze- copying phenomenon is viewed as a key marker of social interaction among the monkeys.

What they found was even though the macaques followed the gaze of another regardless of their status as a friend, family member of dominant member, they responded much more quickly if it was a friend doing the gazing.

'Our main finding is that gaze-following is strongly influenced by the degree of friendship between the macaques,' Mr Micheletta explained.

'Friends did not react more often to the gaze of those who weren't friends, but reacted much faster to friends' gazes regardless of the subtlety or lack of it in the informants' movements.

'Our results suggest that this effect of friendship seems independent of social status and family relationships.'

While it is not known exactly why this marked difference between friends and family exists among the macaques, the researchers speculate that information gained from a friend is likely to be more relevant and useful to the gaze follower than information from a family member.

'Rapidly following the gaze of another might be advantageous in many ways - finding a resource such as food is more likely if competition between friends is reduced, and an individual is more likely to be more concerned about any social event involving a friend,' Mr Micheletta said.

'This is partly so they can help support each other during conflict which helps build social cohesion and stability.'

The researchers also believe that the strength of this bond of friendship could explain how other primates, including humans, develop their social skills.

'Friendship, more than family ties or the status of another, improves the gaze-following ability of this particular macaque species,' Mr Micheletta said . 'It is likely the same applies to other primates, including humans.'

The study's findings have been published by the journal Animal Behaviour.