Only fools and frauds claim to have been abducted by aliens. Right? Wrong, says Susan Clancy, who finds that even eminent professors believe they have fallen foul of ET

Everyone knows how it happens. The aliens come in the night.

When they approach, you can't move. You feel paralysed, terrified and helpless. The creatures are repulsive, with wrap-around black eyes, exiguous fingers and sinewy bodies. They take you away from all that is safe and familiar and probe your brains, nasal cavities, genitals and intestines. They steal your memories and return you to Earth confused and disoriented, unsure what, if anything, happened.

"But it is so unreasonable," a hardcore sceptic recently protested to me. "There is no evidence that extraterrestrials even exist, never mind that they are taking us from our bedrooms. What is wrong with these people?"

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Many scientists have already answered this question. Believers, they say, are totally irrational, cognitively impaired, delusional or, at the very least, hysterical attention-seekers. This cold-shouldering is unfortunate, not because aliens are abducting us - all evidence points to the contrary - but because so many people think that they are. Polls tell us that about 93 per cent of the US population believe that extraterrestrials exist, and that as many as 65 per cent suspect that some have abducted humans. And after five years of interviewing abductees as part of my research into false memory creation, I can assure you that not all believers are poorly educated or especially gullible. Quite a few, in fact, are academics.

Jacob is a tenured history professor at a respected US university who says he was abducted in the late 1980s. "Look," he says, "the idea that people can be taken against their wills by strange humanoids and subjected to intrusive procedures is so shattering to our ideas of what is possible that the phenomenon tends to get rejected out of hand."

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But he argues that thousands of people who were sound of mind and had nothing to gain have reported consistent evidence. "So be sceptical if you want," Jacob says, "but something happened to me, something that defies what modern science dictates."

The late John Mack, a Pulitzer prize-winning member of the Harvard Medical School, was a believer as well. While he himself was never abducted, he spent almost a decade interviewing (and hypnotising) people who said they were. When we met in 2000, he told me that the scepticism came in part from the fact that the West had cut itself off from a global tradition of awareness of any form of higher intelligence. "Although it just doesn't fit into the Western rationalist tradition of science, in my opinion there is no evidence that anything other than what abductees are telling us has happened to them," he said.

While some believers are logically challenged ("the universe is huge, therefore there must be aliens, therefore these stories are probably true") and others are a bit mad ("I am part alien - hybrids will inherit the Earth"), there is no evidence that as a group they are any more cognitively or psychiatrically impaired than the rest us. They may score high on measures of creativity, or proneness to fantasy and intense visual imagery, but so do a lot of people who have never claimed to have had contact with aliens. In fact, if I compare abductees with other groups I have had close contact with - serious vegetarians, yoga enthusiasts, Hollywood actors, psychologists, assistant professors and my family - they really don't look all that different.

Take Robert, the first abductee I ever interviewed. I expected him to be a weird-looking introvert with an active internet-based social life. The man who appeared in my office was a handsome, happily married, articulate chiropractor who had never attended a Star Trek convention or played Dungeons and Dragons . Yes, he believed that he had been abducted by space aliens and then medically and sexually experimented on. But he was sceptical about what happened to him and open to other interpretations. He spoke about his experiences with an appealing mix of self-deprecation, scepticism, humour, fear and surprise.

For Robert, like almost all abductees I interviewed, the seed of his alien abduction belief was a question. Such a question can be simple - "Why did I wake up in the middle of the night unable to move?" or "Why are there odd marks on my back?" - or profound - "Why do I always feel like an outsider looking in on the world?"

The question leads to a search for causes, which people then weigh systematically. One abductee, a chemistry doctorate student, "had a weird dream" in which there were "shadowy figures" around his bed. He woke up with a stabbing genital pain. Familiar with Close Encounters of the Third Kind and similar movies, he wondered if he might have encountered aliens.

Upon reflection, however, he decided that the figures seemed "too tall - I don't think aliens are that tall". Next he considered the possibility that the pain stemmed from a repressed memory of childhood sexual abuse. Then he considered the possibility that the experience was spiritual in nature, but he doubted that angels "would wear hoods". He tentatively settled on the alien abduction explanation, which was later confirmed for him by an "alien abduction researcher".

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When people are looking for the cause of something, their search is limited to those explanations that they have heard of. For most of us, this list is far from complete. "Abductees" are generally unaware of the existence of sleep paralysis, perceptual aberrations, memory distortion or the base rate of feeling empty and alone. But they do know about alien abductions. For better or worse, over the past 40 years, being taken by beings from other worlds has become a culturally available explanation for distress.

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Since the 1950s and 1960s, movies and TV shows have featured aliens, some of whom abducted us, inserted needles into us, exchanged DNA with us and reversed our memories. In the 1970s and 1980s individual accounts - "it-happened-to-me" testimonials - became fodder for bestselling books, films and "documentaries".

It is a safe bet that everyone who watches TV and sees movies "knows" what aliens look like and what they do to us. It shouldn't be surprising that some of them believe the stories are true. Scientists may argue that anecdotal reports don't carry much empirical weight, but most people believe otherwise, especially when what they convey provides an explanation for the confusing experiences or feelings we are having. In the words of a 35-year-old computer programmer at the Massachusetts Institute of Technology: "I don't care what anyone else believes, I'm telling you that things make sense now."

For some, the process of coming to believe they have been abducted culminates in actual memories - detailed, traumatic, autobiographical memories. This generally happens after the believer falls into the hands of an abduction researcher or therapist who uses certain techniques believed to help retrieve lost memories. These methods go by different names - hypnosis, guided imagery, regression therapy, relaxation therapy - but they all work in roughly the same way. The abductee gets lulled into a suggestible state and is then asked to imagine things that either the therapist or the abductees believe might have happened.

But memory isn't a videotape. Memories can be altered over time, and false memories - even emotionally powerful ones - can be created. Thus, it shouldn't be surprising that what often emerges during these sessions "is exactly like what I saw on TV".

Suppose more people knew about the memory-distorting effects of hypnosis, or that anecdotal reports don't count as scientific evidence, or that the probability of alien life on Earth is infinitesimally low. Would this reduce the number of believers?

I doubt it. When people are sorting through possible explanations for strange symptoms and experiences, they don't rely on abstract principles of parsimony or probability. They rely on what seems to fit and what feels right.

For many experiencers (as they like to be called), being abducted by aliens not only explains their psychological distress and unsettling experiences, it provides meaning for their entire life. Many of us go through life trying on belief systems for size. Some of these beliefs speak to powerful emotional needs that have little to do with science - the need to feel less alone in the world, the desire to have special powers, the longing to know that there is something important out there watching over you. For many, belief in aliens gratifies spiritual hungers. Although initially terrifying and painful, it reassures them about their own significance in a universe that is not dark, cold and empty. As abductee after abductee said to me, "it enlarged my world-view", "expanded my reality", "caused me to care about the spiritual path of mankind". One put it like this: "These beings are like God's angels, in a very roundabout way - like messengers. Out of my aloneness I have discovered oneness with the universe."

Susan Clancy is a postdoctoral fellow in psychology at Harvard University. Her book Abducted: How People Come to Believe they were Kidnapped by Aliens is published by Harvard University Press, ?14.95. The Science of Aliens exhibition opens at the Science Museum, London, on October 15, accompanied by a series of debates at the Dana Centre.

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