Religion is the key to understanding why human beings are more intelligent and social than any animal in the world,according to an eminent Oxford professor.

'You need something quite literally to stop everybody from killing everybody else out of just crossness,' said Robin Dunbar, professor of evolutionary psychology. 'Somehow it's clear that religions, all these doctrinal religions, create the sense that we're all one family,' he added, according to the Washington Post.

Dunbar is known for his research more than twenty years ago on the size of animals' social networks. He found that each species of primate can manage to keep up a social bond with a certain number of other members of its own species, with that number going up as primates' brain size increases.

The scientist found that humans are capable of maintaining significantly more social ties than the size of our brains alone could explain. According to his research, each human is surprisingly consistent in the number of social ties we can maintain: around five with intimate friends, 50 with good friends, 150 with friends and 1,500 with people we could recognise by name. This discovery became known as 'Dunbar's number'.

Now, Dunbar believes that religion explains why the number is so high among humans. 'Most of these things we're looking at, you get in religion in one form or another,' he said.

Dunbar's research is part of a trend in favour of looking at religion as a benefit to civilisation, rather than something that adds to ignorance.

Christian Smith, a sociologist at the University of Notre Dame who studies religion, said: 'For most of Western intellectual history since the Enlightenment, religion has been thought of as ignorant and strange and an aberration and something that gets in the way of reason.

'In the last 10 or 20 years on many fronts, there's been a change in thinking about religion, where a lot of neuroscientists have been saying religion is totally natural. It totally makes sense that we're religious. Religion has served a lot of important functions in developing societies.'

Dunbar puts religion in a category with laughter and singing which help explain humans' remarkable social networks. 'These three things are very good at triggering endorphins, making us feel bonded,' he said last week at the American Association for the Advancement of Science's annual meeting.

Repetitive motion triggers endorphins, said Dunbar, noting that traditions from Catholicism to Islam to Buddhism to Hinduism make use of prayer beads.

Researchers have also shown that doing these activities in synchronised fashion with other people, such as the coordinated bowing that Muslims, Catholics and Jews all take part in, drastically magnifies the endorphin-producing effect.

'What you get from dance and singing on its own is a sense of belonging. It happens very quickly. What happens, I suspect, is that it can trigger very easily trance states,' Dunbar said. 'Once you've triggered that, you're in, I think, a different ballgame. It ramps up massively. That's what's triggered. There's something there.'