Bonk, by Mary Roach

Secrets of the orgasm machine

Californian reporter Mary Roach puts her quick wit to good service in this entertaining romp through sex research, past and present. Keenly attuned to what she calls the "cringe factor", she manages to describe the nitty-gritty of genitalia in action without making you wish she hadn't. While she's sympathetic to scientists' desire to demystify sex and to help people with sexual problems, her sense of the ridiculous supplies regular doses of comic relief.

In her quest for the latest insights, Roach visits sex research labs in London, Cairo, and Taiwan as well as the US. All are premised on the conviction that human sexuality is as worthy of scientific study as "sleep or digestion or exfoliation". Yet even today, there's the unspoken assumption that "people study sex because they are perverts," says Roach. "It wasn't until the past half century that lab-based science embraced the pursuit of better, more satisfying sex."

The sex laboratory came of age with the ground-breaking investigations of William Masters and Virginia Johnson. Their 1966 classic, Human Sexual Response, described, in great detail and for the first time, the physiology of arousal and orgasm. But much of their data arose from their bizarre invention of an artificial-coition machine: "a thrusting mechanical penis camera that filmed – from the inside – their [female subjects'] physical responses to it." This is "as good as science gets," she writes, "a mildy outrageous, terrifically courageous, seemingly efficacious display of creative problem-solving, fuelled by a bullheaded dedication to amassing facts and dispelling myths".

Roach attempts to track down the device, and puzzles over why or how so many female volunteers seem to have reached orgasm from nothing more than "the straight-on, in-and-out motions of a plastic phallus". Her investigations lead on to a highly sceptical encounter with "sex machines" on sale in San Francisco (vibrators seemed to be a crucial adjunct), and DIY measurements of the distance between clitoris and vagina. There's a theory that the greater the distance, the more elusive orgasms via penetrative sex with little or no clitoral stimulation.

On this roller-coaster ride, Roach is soon off investigating whether orgasm boosts fertility, which entails a visit to a crack Danish pig unit where farmers sexually stimulate sows during artificial insemination to boost fertility rates. She visits Topco, a sex-toy manufacturer, where she's shown an array of plastic penises, vaginas and anuses, modelled on plaster casts of top porn stars. At one point, in the interests of science and reportage, she and her husband Ed try to have sex while being scanned by a researcher wielding an ultrasound wand. Ed wisely takes Viagra beforehand.

She tackles treatments for impotence – everything from pumps and penile prostheses to Kegeling – as well as research into what might be the female equivalent of male erectile dysfunction. If "clitoral erectile insufficiency" really exists, a female equivalent of the penis pump might help, by increasing blood flow to the clitoris. Roach bravely tries one out, while pursuing the cheery notion that masturbation might be good for your health.

Later, in the interests of science, she finds herself watching porn films with a photoplethysmograph probe in her vagina. If that sounds sensationalist, it is – yet Roach packs in plenty of intriguing findings, served up with level-headed critiques and refreshing scepticism.

She has done her homework and appended a bibliography so that readers can track down the primary sources. Her unshockability is contagious, and ultimately reassuring. When Roach began researching her book, she "harbored a naive fantasy that I would find a team of scientists working to discover the secret to amazing, mind-rippling sex". In the end, the secret is to be found in a little-noticed book by Masters and Johnson, published in 1979.

Called Homosexuality in Perspective, it concluded that the best sex they had observed was that between the committed gay and lesbian couples – not because these couples had any special homosexual techniques but because they "took their time" and took pleasure in their partner's responses, which the "goal-orientated" heterosexuals rarely did.

Thirty years on, even straight sex has improved, Roach reckons, as communication between partners becomes more open and less inhibited. Sex researchers can surely claim some of the credit, along with irrepressible popularisers like Mary Roach.