For what are sex researchers supposed to be like to win our trust and respect? White-coated technicians, solemnly observing experiments then writing up the findings? Or louche hedonists, who like to talk sex, think sex, do sex every waking hour? Nerd or perv? Neither image does much to inspire confidence.
The problem is made worse because sex research isn't exactly a profession. Unlike other sex industries, it doesn't make money. Only with subsidy can it go about its business, and potential sponsors can't help but be sensitive about what exactly it is they're sponsoring. In 1989, the British government withdrew its support for the largest ever survey of sexual behaviour in this country, saying that its involvement would be "inappropriate" ("Thatcher Halts Survey on Sex" ran the headline in the Sunday Times). There have been similar climbdowns in the US, Switzerland and even Sweden. Beneath them all lurks an innate prejudice against sex research: nice work if you can get it, but a waste of public money and time.
Though he was first in the field, Alfred C Kinsey, the grandaddy of sex research, was well aware of this prejudice. This was why, when he published Sexual Behaviour in the Human Male 50 years ago in January, he took enormous care to present an acceptable authorial face to the world: that of a diligent, abstemious, wholesome family man whose only interest in having spent more than a decade asking men about the size of their organs, or the frequency of their orgasms, was the advancement of human knowledge. For the companion report on the human female five years later, he insisted even more strenuously on his scientific credentials. The media might present him as "Dr Sex" - the boffin of bonking - but in his own mind he was a trailblazer, a Darwin or a Galileo battling against the forces of darkness, whose discoveries would alter the modern world.
Kinsey couldn't have predicted the instant public clamour for his work (200,000 hardback copies of the first volume were sold in two months in America alone) but he knew that his findings would shock. In 1948, sexual anatomy was, to the majority of Americans and Brits the vague uncharted land of Down There. Like a cartographer, Kinsey brought us maps - and, like Mr Gradgrind, facts, facts, facts. That the phallus varies in size "from non-existence to a maximum length of 13 inches"; that the vagina varies in depth from 1.7 inches to 5.4 inches; that the average male between adolescence and 30 has 2.88 orgasms per week; that women don't reach their sexual maturity till their late twenties, 10 years after men have begun to decline - information like this simply hadn't been available in the age of Hush and Pretend.
Much more shocking, though, was what his research revealed about the diversity of sexual activity in the US, only a fraction of which was sanctioned by custom or law. At a time when convention allowed only for missionary- position sex within marriage, Kinsey revealed just how many men (95 per cent) were deviant, because they did it before marriage (85 per cent) or extramaritally (45 per cent) or orally (59 per cent) or with prostitutes (70 per cent) or with other men (37 per cent) or with animals (17 per cent of farm boys) and above all, onanistically, to themselves (85 per cent). For the companion female volume five years later, the figures were less spectacular and now look positively tame: if it were reported today that only 62 per cent of women masturbated, and only 50 per cent had premarital intercourse, we'd worry about all the others missing out. But in an America of apple-pie moms and I Love Lucy family values, such statistics were deeply disturbing.
This was why Kinsey felt it so important to stress his "monotonously normal" (as Time magazine put it) private life. Countless interviewers duly relayed this message to the world, presenting a husky fellow with a nice smile who didn't swear, smoke or drink and seemingly had no vices at all.
Now, thanks to a new 900-page biography by the American historian James H Jones, we know that Kinsey was far from being the Mr Average he pretended to be.
There was his masochism for a start. One of his favourite stunts - an accompaniment to masturbation - was to insert an object into his urethra, tie a rope round his scrotum, and then tug hard on the rope as he manoeuvred the object deeper. Early on, it was straws he inserted. Later he progressed to pipe cleaners, pencils and toothbrushes (in time, with practice, the brush end first). Finally came an incident when he refined this art of self-torture by suspending himself in mid-air, causing damage to his pelvic region and possibly even hastening his own death.
We know about Kinsey's masochism because he liked to film himself in the act. He liked to film and watch others having sex, too - all in the name of scientific objectivity. A colleague invited along to one of these demonstrations later recalled Kinsey getting in so close to a couple making love that he "was virtually on top of the action, his head only inches removed from the couple's genitals". Characteristically, he could be heard above the moans, pointing out the various signs of sexual arousal. It was in the same spirit that Kinsey imported collections of erotica for the library at his Institute for Sex Research, fighting battles with customs officers who considered the materials not knowledge but "filth".
Then there were the evenings when members of his research team and their wives would be invited round to his house. These began as occasions for listening to classical music, but as time passed they turned into group sex sessions in his attic, some of them again recorded on film. Kinsey wasn't much of a fun-lover (his face, when he had sex, looked unrelievedly grim), and he didn't like members of his research team having extra-marital affairs, unless they had asked him for permission. But he regarded these sessions as experiments in the creation of a sexual utopia, with himself in charge of every move. His own wife Clara set a stalwart example, enthusiastically bedding whomever he chose for her. Because she was a small, mousy, deeply devoted mother of three, some said that she co-operated primarily to please and hang on to him. It's just as likely, though, that she was gratified by the attentions of the younger men he put her way, especially when sexual relations with "Prok" (as she called her husband) began to tail off.
For Kinsey's real sexual interests lay elsewhere, not only non-connubially, but with men. It was largely thanks to his research that he was able to pursue them. Field trips to Chicago and New York put him in touch with a thriving gay subculture, in which he felt happy and at home. As a young man, he'd been ashamed of his homosexuality. Now he could express it - and help other gay men to realise there was nothing abnormal about their desires. Kinsey was a skilful interviewer, and through his sympathy and desire to liberalise built up a huge network of underground contacts. On one occasion, for example, in order to determine whether men, upon orgasm, "squirt out" or merely "dribble" (a typically cranky and mechanistic Kinsey inquiry), he said that he needed to film 2,000 volunteers masturbating to climax, and would pay them two dollars each. At once, his contacts in New York came up with the goods, mustering a line of volunteers which stretched along the sidewalk and right round the block.
NUMBERS were Kinsey's special thing. For 20 years before he got into sex research, he had been a biologist. His specialism was the gall wasp, and what set him apart from other experts in the insect field was the sheer number of specimens he collected. His field trips were months'-long, dawn-to-midnight ordeals, horrendous for his helpers, masochistically enthralling for him. His ambition was to collect 1.5 million samples. He personally examined 35,000 gall waps, and made 700,000 separate measurements. He'd have gone on to collect every specimen on the planet if he could.
Taxonomy continued to be the basis of his research when, having failed to take the world by storm with his book The Gall Wasp Genus Cynips, he gradually moved across to the study of humans. His opportunity came when he volunteered to teach a "marriage course" at his university, in Indiana. Until then, he'd been a stiff, conventional man whose only known quirk was a habit of gardening in a loincloth. The course liberated him, and he captivated students with his uninhibited anatomical discussion.
Needless to say, as with everything Kinsey did, there was a personal subtext. As a bookish, sickly child, he had been traumatised by the sort of let's-show-each-other-our-naughty-bits game which most children take in their stride. As a clean-cut, religious-minded teenager, he'd been made to feel horribly guilty about masturbating. As a new husband, he'd failed to consummate his marriage with Clara (a virgin like him) for several months. All these difficulties he attributed to ignorance, and was determined that his children's generation wouldn't suffer the prudish upbringing he'd had. As their children grew up, he and Clara became famous for dispensing useful advice to the whole neighbourhood. The marriage course grew out of these informal beginnings.
It was by inviting students to have post-lecture "personal conferences" with him that he assembled his first few sexual histories. He preferred oral interviews to written questionnaires, rightly believing that he could thereby prise more out of his subjects. In time, by being guaranteed anonymity, almost everyone he met was bullied into answering his questions. He even interviewed his own wife and children. In time, as he assembled a team around him, he didn't have to interview everyone himself. But he did his best, regularly working an 18-hour day. By the time he died (worn out, at 62), he had personally interviewed 7,985 subjects (an average of more than nine a week for 17 years). Interviewing is a form of penetration, and he seems to have derived a libidinous thrill from it. But the mask of impersonality remained in place. He continued to present himself as an apostle of progress, a soldier of science, a secular evangelist.
Even in his lifetime, Kinsey's research methods were criticised. His East Coast bias, his eagerness to interview homosexuals ("I can pick them up at five to seven per day," he wrote excitedly to a friend), his failure to use or understand random sampling - all these came under scrutiny. Fifty years on, several other aspects of his work look dubious. One is his treatment of women, whom he reported as having less sex drive than men. It didn't help that Kinsey employed almost no women in his team, and that he thought the frisky Clara eager for sex on his behalf, not her own. Having read his findings, one indignant single mother from the Midwest, beating him at the numbers game, wrote to say that she personally averaged 130 orgasms a month and that a friend of hers, using a dildo, had come 100 times in one night. Even without such figures, it's clear that Kinsey - something of a Victorian patriarch, for all his Lawrentian iconoclasm - underestimated the female libido.
Even more dubious, from current perspectives, is his attitude to sex with children, laws against which he seems to have regarded as pointless and outdated. His reports included material on infants being timed to orgasm, much of which had come from the mysterious "Mr X", a man who boasted of having had sex with 600 boys and 200 girls. Kinsey was fascinated by Mr X (whose prodigious feats included the ability, at 63, to start from a flaccid state and ejaculate within 10 seconds) and saw him, not as a dangerous paedophile who deserved to be in prison, but as a courageous rebel and fellow seeker. It was only conditioning, Kinsey thought, that made children fear and feel traumatised by sexual contact with adults. Molestation, he said, could often involve affection, and the "very few cases of vaginal bleeding" that sometimes resulted "did not appear to do any appreciable damage". The harm, he concluded, was all in people's minds. Such was his sympathy for sex offenders that he stopped seeing the abusive nature of their offences.
Kinsey was wise to have concealed much of what he thought and did. If the three institutions which supported his research - the University of Indiana, the Rockefeller Foundation and the National Research Council - had known more than a fraction of what he got up to in private, they'd surely have cut him off. As it was, there were repeated rows over his work, and, in the McCarthy era, FBI investigations into his political affiliations (his reports, like Communism, were seen as a threat to the American way of life). Thanks to the courageous support of a handful of seemingly faceless bureaucrats, the funding by and large continued. Other men might have felt grateful for that support. But Kinsey, perverse to the end, died paranoid and embittered.
It's ironic that, in order to turn the lights on his nation's sexual activities, Kinsey had to keep his own walled up in the dark. Now, with James Jones's revelations, his secret is out, and we can see how his own sexual agenda skued some of the conclusions at which he arrived. But that doesn't mean his efforts were wasted. Through luck and cunning, he was able to carry out important, ground-breaking research and to usher in a more candid age - and we should all be grateful for that. Kinsey did his best to take the worry and guilt out of sex. If we continue to feel worried and guilty sometimes, it isn't his fault but the nature of the beast.
'Alfred C Kinsey: A Public / Private Life' (Norton, pounds 28) by James H Jones is out on Wednesday.