In the first flush of love, Jennifer* and her partner, Simon*, had enjoyed a satisfying, if sporadic, sex life. But as time passed, they fell into a familiar pattern that had all the coded intricacy of a formal dance. First came Simon's gentle approach, with perhaps a kiss or caress. Next, Jennifer, 29, would respond by saying she was tired or had a headache, or wasn't in the mood.
And Simon, 30, who hates confrontation, would turn away from her in defeat. No-one expressed their real feelings - that is, until one fateful night last year when all of Simon's frustration spilled out in a torrent of sadness and anger.
"He said he was sick of the rejection," confesses Jennifer, an office manager from Sydney. "He didn't want to pressure me, or force me in any way, but he felt like that was happening and he didn't like it." Constant rejection and months without sex had made Simon, a lawyer, question whether Jennifer was really attracted to him. More than that, he desperately wanted his partner to share his desire for sex. "He said he wanted me to really want it," she recalls. The problem for Jennifer was that she never really had.
From scantily clad women gyrating suggestively in music videos to the provocative ads that wallpaper our lives, we live in what Sydney sex therapist Tanya Koens describes as a "high-libido world". Desiring sex - a lot of sex - is now seen as the norm, she observes. Yet like Jennifer, many women simply aren't that interested. In one survey, 32 per cent of sexually active women reported a lack of libido over several months or more in the previous year; other studies have placed that figure as high as 43 per cent. The story is very different for men, who consistently report a higher sex drive and much lower rates of loss of libido.
The question of what turns women on has proved elusive. Recently, though, that has started to change. Thanks to a pioneering group of women in the US and Canada, our sexuality has been under the microscope like never before - and the findings have been surprising. Far from being less sexual, it seems women are aroused more easily than men. We value the intimacy and security of relationships, but there's growing evidence that being in a relationship simply isn't good for our libido. And overall, it seems women's sexual response works in a different way to men's.
That's just one of the reasons why comparing our sexual desire to men - and even to one another - is futile, argues psychiatrist Professor Leonore Tiefer, from the New York University School of Medicine. "There is no normal level of sexual desire," she says. "What's normal for you may not be normal for me, certainly wasn't normal for my mother. This is a very varying thing."
For Jennifer, who describes herself as having "zero libido", sex has become the issue that could either cement her five-year relationship or tear it apart. "I wish I desired it every single day," she says. "But I don't know how the 'every single day' people do it. I feel like something is missing. Sex is something that binds you to each other, unique to any other relationship in your life.
When she looks back through her relationship history, Jennifer finds it hard to work out whether her libido has fallen, or if she has always had little interest in sex.
Her previous relationship was emotionally turbulent and "it was more like, I want this man to stay with me so I'll have sex with him".
Simon, she feels, is the first man who has desired her for a host of reasons, not only sexual, and this new-found sense of security has removed some of the impetus for sex. Yet Jennifer does enjoy sex once it's underway, and she does orgasm.
"It's not like I don't get horny; it just takes a lot for me to really get into it," she admits. "Sex when I'm drunk is way better because I'm relaxed. I think I go through the motions a bit; I'm very self-conscious when it comes to sex - it doesn't feel natural or comfortable and it never, ever has."
This self-consciousness or sense of disconnection during sex is the focus of work by two researchers, Professor Meredith Chivers, a psychology professor at Canada's Queen's University in Ontario, and Dr Lori Brotto, a psychologist at the BC Centre for Sexual Medicine in Vancouver.
In one experiment, Professor Chivers hooked up men and women to a plethysmograph, a scientific apparatus that measures physical arousal in terms of blood flow to the penis and vaginal lubrication.
She then showed them a series of videos that included heterosexual sex, gay sex, masturbation, bonobo monkeys mating, a naked man walking on a beach, and a naked woman exercising.
For each video, Professor Chivers' subjects were asked to rate how turned on they felt (their subjective arousal), while the plethysmographs measured how physically aroused they were.
The men responded pretty much according to their sexual orientation: straight men were physically aroused by heterosexual sex and lesbian sex, and they rated those couplings highly, too.
"Their minds and genitals were in agreement," wrote Daniel Bergner in his New York Times account of the experiment in January 2009. But the women's results were very different. They were physically aroused by all the human scenes and even, to a lesser degree, the bonobos.
But their self-reporting wasn't as clear. "During shots of lesbian coupling, heterosexual women reported less excitement than their vaginas indicated; watching gay men, they reported a great deal less; and viewing heterosexual intercourse, they reported much more," says Bergner.
In short, the women's minds were at odds with their bodies. In fact, it seemed many kinds of sexual activity could turn women on physically - not just the activity they consciously expressed a preference for.
In Vancouver, Dr Brotto is working to help bridge that gap between our bodies and minds by using the Buddhist technique of mindfulness. "Many women tell us they don't feel connected to their bodies," she says, or they're so distracted by the everyday worries of life that they fail to read their body's physical cues.
Treatment starts with nonsexual exercises: for example, her patients are asked to observe their bodies in the shower and "notice the sensation of the water on their skin"; later, they're asked to look at their genitals and explore mental fantasies with a vibrator.
Generally, patients attend 6 - 12 sessions and so far Dr Brotto's results have been promising. Many patients say they feel less distress as soon as treatment begins.
The two researchers' work supports the idea that women's sexual desire works differently to men's. "Men's sexual process is pretty linear - moving from desire to arousal to erection, sexual activity and ejaculation, followed by a wait until the next erection," says Koens. Women's desire, on the other hand, is "responsive", explains Dr Goldmeier.
"Often, for women, the desire for sex comes after the mental decision," agrees Sydney sex coach and therapist Jacqueline Hellyer*.
That's certainly the case for Jennifer, who admits she "got a bit lazy. About six months ago, we went for three months without sex, and Simon had to remind me of that." Now, they talk about sex and make time for it.
To Professor Marta Meana, of the University of Nevada in Las Vegas, Jennifer's complaint is one she's heard time and again in her work with women who have low libido.
Yet she has an interesting take on the topic. In a study published in the Journal Of Sex & Marital Therapy last July, she and colleague Karen Sims asked 19 married women, with an average age of 31.5, why they thought their sex drive had fallen.
"Marriage was generally spoken about as a passage from independence, freedom, and excitement to one of commitment, responsibility and routine," reveals Professor Meana.
In some ways, there's nothing particularly new about comments like this - as Professor Meana and Sims admit, "there is an entire industry of books, videos and workshops aimed at helping married couples recover and resuscitate flagging sex lives".
But where many experts emphasise closeness and intimacy as key factors in women's desire, Professor Meana argues the opposite - that "closeness had led to familiarity, which had too often led to efficient, but boring sex".
Although all the women in her study loved their husbands and were otherwise happily married, they confessed to feeling that their sex drive would recover if they had sex with a new partner.
When it came to sex, stated Professor Meana, perhaps women needed excitement and novelty just as much as men - an observation that certainly flies in the face of convention.
Professor Meana isn't advocating infidelity, but she and Sims do suggest some ways to improve desire. "The way women feel about themselves is the single most important factor in whether they feel desire," she says.
If a woman doesn't feel sexy, she can interpret her partner's approaches as being more about the desire for an orgasm than a desire to have sex with her in particular.
"But if women have judged themselves to be desirable, they see an approach as personal." She encourages patients to work out how to feel better about themselves, whether that’s through intellectual achievement, exercise or investing in sexy underwear.
"It's very individualised. We look at what makes them feel sexy and what barriers stand in the way."
It's also important to "change tired sexual scripts". Professor Meana likes to quote fellow sexologist and psychologist Professor Peggy Kleinplatz, who once declared, "Nothing kills sexual desire as much as doing what works - relentlessly."
Too often, couples in long-term relationships know the most effective way to get each other to orgasm, which can make sex seem boring and mechanical. "Sometimes, to change this, couples have to give up the assuredness that orgasm will happen," says Professor Meana.
"They need to mix up the time and location, break the sequence of how sex starts and ends." She argues that couples need to practise mindfulness, training themselves to notice how sexual activity actually feels.Stoking sexual desire takes work, she adds. She likes to imagine desire as a continuum, with comforting closeness at one end and extremely erotic activity at the other. "Women and their partners have to work out where they feel comfortable along that scale, knowing that relationships will constantly be pushing them towards familiarity," says Professor Meana. "Successful relationships demand lifelong effort."