They are issues that have been baffling scientists for generations and terrifying the rest of us throughout recorded history – do ghosts exist? Is there life after death? Is there a God watching over us?

Bristol University academic Professor Bruce Hood may not be able to answer any of these questions, but he has developed a theory as to why we ask them in the first place.

American-born Professor Hood believes all superstitious behaviour ranging from crossing your fingers for good luck to a fully-fledged religious belief system has a basis in our intuitive childhood psychology.

In his 20th year at the university's Priory Road Department of Psychology, the academic has published a book that promises to answer many of mankind's most enduring questions.

In the new book, SuperSense: From Superstition to Religion – the Brain Science of Belief, Professor Hood explores where such beliefs come from, and the book is proving an unlikely bestseller around the globe.

Most of us recognise traditional superstitious customs such as knocking on wood or not walking under ladders.

David Beckham only has an even number of drinks cans in his fridge and Tony Blair always wore the same shoes during Prime Minister's Question Time.

However, Professor Hood argues that such beliefs and practices are the norm and not the exception. In a US Gallop poll of 1,000 adults conducted in 2005, 73 per cent said they believed in at least one supernatural phenomenon, ranging from extrasensory perception (ESP) to ghosts, telepathy and reincarnation.

Where do such beliefs come from? One might assume that we get our beliefs from others but according to Professor Hood, who is Professor of Developmental Psychology at the University, many supernatural beliefs have their origins in the way that children spontaneously think about the world.

"As children," he explains, "we generate knowledge through intuitive reasoning about the world around us, which leads to both natural and supernatural beliefs.

"With scientific education we learn that supernatural beliefs are irrational, but because they operate at an intuitive level they can either be resistant to reason or lie dormant in otherwise rational adults."

If Professor Hood is correct, then it is unlikely that any effort to get rid of supernatural beliefs, or the superstitious behaviours that accompany them, will be ultimately successful. Moreover, he argues, these beliefs may be adaptive in binding us together as social groups.

"We are pre-wired with a mind design that creates a 'supersense' that shapes our intuitions and superstitions and is essential to the way we learn to understand the world," he says, as he settles himself into his chair in his book-lined Priory Road office.

"When you look at things like childhood beliefs, many are universal – they're there in every culture across the world – so you have to conclude there is something fundamental about them that suggests these are ways our brains naturally work.

"When we're young our brain makes lots of assumptions, as it constantly battles to get to grips with understanding the world around us.

"For example, the notion that we cease to exist after we die is too difficult to comprehend for a child, so they assume that there is an afterlife. Therefore it is easy to assume that ghosts exist. We may be able to tell ourselves intellectually that this isn't the case as we grow older, but it's very difficult to change our intuitive brain."

Professor Hood's career as a child psychologist has taken him from Harvard University and the Massachusetts Institute of Technology (MIT) to stints teaching at Cambridge before eventually coming to Bristol in 1999. But it was only four years ago, that he began to turn his attention to belief in the supernatural.

"I watched the way my young daughter imbued a sense of great importance on a particular comfort blanket," he says. "So I devised an experiment where I told children I had a special machine that could reproduce any item perfectly – like a three-dimensional photocopier.

"I convinced them that it worked through trickery, but it was interesting to see how reluctant they were to allow their comfort blanket to be cloned. There was something special about their blanket that an identical copy didn't have.

"This happens with all kinds of treasured possessions. We imbue a certain uniqueness on them – what I call an essence. This is very important to people, even though it clearly doesn't exist."

The professor has proved this belief continues into adulthood with a series of experiments.

"In one experiment I produce a pen and tell the volunteers that it belonged to Albert Einstein. When I ask, everyone in the room is keen to hold the pen – almost as if Einstein's genius in imbued in it.

"Then I produce a cardigan and ask if anyone will wear it for a £20 reward. Lots of hands go up. But when I then tell them the cardigan belonged to the serial killer Fred West, almost all the hands immediately go down.

"It's as if the cardigan is somehow imbued with the evil of the killer. Rationally we know that Fred West can't do anything to us via his cardigan, but we find it almost impossible to shake off this notion that the garment is somehow contaminated by him.

"We all tend to give objects what we call essentialist meanings. A child knows a dog is not a cat, even if you change its body into a cat's body. Inside they believe it is still a dog. In fact it is – we know that it would still have the DNA of a dog, but children understand this on a more intuitive level.

"That's why most cultures tend to have a creationist theory as a basis of belief. Children tend to be able to get their heads around Creationism much more easily than Darwinian evolution.

"This is one of the reasons why religion is so enduring. It plays an important part in society, because it creates a focus for belief, and the human mind tends to need to believe in supernatural things.

"When you look at countries like Russia and China, where governments have tried to suppress religion, it has always endured, and even returned stronger within the society."

Professor Hood believes his book, which has been published in eight countries, will be easily accessible to non-academics – and it could sell well in the wake of best-selling books such as Professor Richard Dawkins' The God Delusion.

It has already received rave reviews in the New Scientist and the Guardian, and is riding high in online retailer Amazon.co.uk's top 500 bestsellers.

"Reading the book will almost be like a crash-course in philosophy," he says. "I've covered a lot of areas that fascinate people – from ghost belief to extra-sensory perception and superstitious ritual. This is stuff everyone wants to understand."

SuperSense: From Superstition to Religion – the Brain Science of Belief, by Professor Bruce Hood, is published by Constable & Robinson, priced £8.99.