What REALLY makes a woman want to sleep with a man?
What makes a woman want to sleep with a man? Is it true that a chap can laugh a woman into bed? Does he need to be tall, dark and handsome to stand any chance at all?
Today, in the second extract from the new book Why Women Have Sex, by psychologists Cindy Meston and David Buss, we reveal the features that make a man appeal to a woman, and why, are far more fascinating and complex than you could imagine...
Rules of attraction: A fascinating guide to the complex features that will make a man appeal to a woman
Checklist: Can a man really laugh a woman into bed?
What sort of body does a woman find desirable? Perhaps the most obvious physical characteristic she looks for in a man is height.
Studies consistently find that women consider tall men to be attractive. In analyses of personal ads, 80 per cent of women state they want to meet a man who is 6ft or taller.
Men who indicate in their personal ads that they are tall have also been shown to receive far more responses from women.
Other studies show women prefer tall men as husbands and put an even greater emphasis on height in shorter-term sex partners. Women even place importance on height when selecting sperm donors.
Two studies also found that taller-than-average men tend to have a greater number of live-in girlfriends and more children, confirming their popularity for romance and reproduction.
And there does seem to be an underlying logic in women's preference for tall men. In Western cultures, tall men tend to have higher socio-economic status than short men.
Each added inch of height has been shown to add several thousand pounds to a man's annual salary.
It is estimated that, on average, 6ft men earn more than £100,000 across a 30-year career than 5ft 5in men.
They also tend to be healthier than shorter men - and if they're policemen, they get assaulted less than their shorter colleagues, which suggests height commands more respect from other men. What more could a girl want?
THE SCENT OF SEX
According to new scientific research, a woman will literally sniff out a man's genetic make-up before she decides if he's right for her.
A woman's sense of smell reaches a peak around the time of her ovulation, the 24-hour window -during the monthly menstrual cycle in which she can become pregnant.
The genes responsible for fighting off disease-causing bacteria and viruses are found in a group of genes called the major histocompatibility complex, or MHC.
Different people have various versions of these genes - and it turns out that women can benefit in two ways from mating with men whose MHC genes are dissimilar to their own.
Such a mate is likely to have more dissimilar genes in general, so finding someone dissimilar attractive might help to prevent many of the birth defects associated with reproducing with close genetic relatives.
Sexy tone: Voice pitch is the most striking feature of human speech n]
A second benefit is any children of such a union will have a more robust immune system.
The interesting thing is that women seem to be able to sniff out men with dissimilar MHC.
In a revealing study, Brazilian researchers asked 29 men to wear cotton skin patches for five days to absorb their sweat - and thus their body odours.
A sample of 29 women then smelled each cotton patch and evaluated the odour on a scale from attractive to unattractive.
Scientists identified the specific MHC complex of each man and woman through blood tests. Women found the aromas of men who had a complex dissimilar to their own to be the most desirable.
The odours of men who had a complex similar to their own made them recoil in disgust.
This highly developed sense of smell can have a profound effect on women's sexuality.
Evolutionary psychologist Christine Garver-Apgar studied MHC similarity in 48 couples.
They found that as the degree of similarity between each woman and man increased, the woman's sexual responsiveness to her partner decreased.
Women whose partners had similar genes reported wanting to have sex less often. They had less motivation to please their partner sexually compared to the women going out with men with dissimilar genes.
Women with MHC-similar partners also reported more frequent sexual fantasies about other men, particularly at the most fertile phase of their ovulation cycle.
And their sexual fantasies about other men did not just remain in their heads. They also reported higher rates of sexual infidelity.
FIT FOR SEX
Height is not the only aspect of men's bodies that excites women.
Studies of mate preferences reveal that women desire strong, muscular, athletic men for long-term partnerships as well as for sexual liaisons.
Most women also show a distinct preference for a V-shaped torso - broad shoulders relative to hips. They are also attracted to a lean stomach combined with a muscular (but not muscle-bound) upper torso.
In fact, both sexes judge men with a high shoulder-to-hip ratio to be more physically and socially dominant.
This may give a clue to its appeal, since women are not attracted to men who appear as though they could be easily dominated by other men.
Men with a high shoulder-to-hip ratio begin having sexual intercourse at an early age - 16 or younger.
Sexual attraction: A woman will literally sniff out a man's genetic make-up before she decides if he's right for her
They report having more sex partners than their slim-shouldered peers. But be warned: they have more affairs while in a relationship.
And they report more instances of being chosen by women who are already in relationships for affairs on the side.
Scientific research, though, has discovered that men overestimate the degree of muscularity that women find attractive, assuming they need to pump iron and sport a honed six-pack to be attractive.
Images of muscle-bound men have almost certainly fostered men's misperception of what women find most sexually attractive - just as photo spreads of impossibly thin models have led women to overestimate the degree of thinness that men find most attractive.
One study compared the muscularity of men's bodies in Cosmopolitan magazine (whose readership is 89 per cent women) with Men's Health (whose readership is 85 per cent men).
The level of muscularity in Cosmopolitan was nearly identical to that which women rate as ideal in a sexual partner. Men, in contrast, mistakenly believe women desire a more muscular sex partner, which corresponds more closely with the muscularity of men in Men's Health.
After viewing repeated images of V-shaped bodies, men become more dissatisfied with their own bodies, just as women become more unhappy with their bodies after seeing images of size zero models.
THE FACE OF ATTRACTION
When it comes to choosing between a rugged, conventionally handsome man and an ordinary, less attractive partner, women have a difficult choice to make.
In a series of scientific studies, women found square-jawed, masculine faces to be the sexiest and the most attractive for a casual sexual encounter.
But they judged somewhat less masculine faces to be more attractive for a long-term relationship.
Women's sexual desires for testosterone-fuelled facial cues of masculinity were especially strong during the fertile window of their cycle.
The most plausible interpretation of these results is that women are attracted to men who are likely to be 'good dads' when choosing long-term mates, but are attracted to the signals of robust health that more masculine faces provide when they are most likely to become impregnated.
Why do more masculine faces signify health? High testosterone production actually compromises the body's immune functioning, leaving men less able to fight off diseases and parasites in adolescence.
Only men who are above average in healthiness during adolescence can 'afford' to produce the high levels of testosterone that masculinise the face.
Less healthy adolescents can't afford to compromise their already precarious immune systems, and so produce lower levels of testosterone at precisely the time when facial bones take their adult form.
So, a masculine-looking face signals a man's health, his ability to succeed in competing with other men and his ability to protect.
This interpretation, however, raises a puzzle: Why wouldn't women be attracted to highly masculine males for all mating relationships, from dangerous liaisons through to life-long love?
The answer lies in the fact that the more masculine men, with more testosterone, tend to be less sexually faithful.
They are more likely to be the risk-taking, womanising bad boys among the male population.
Consequently, most women face a trade- off: if they choose the less masculine-looking man, they are likely to get a better father and sexually loyal mate, but they lose out in the currency of genes for good health.
If they choose the more masculine man, they can endow their children with good genes for health, but must suffer the costs of a man who channels some of his sexual energy toward other women. It's a tricky choice.
A SEXY VOICE
Voice pitch is the most striking feature of human speech and, according to research, there is a definite sound of sexiness - something about male voices that gives women a sexual buzz.
Before puberty, male and female voices are similar. At puberty, however, remarkable changes occur. Boys experience a dramatic increase in the length of their vocal cords, which become 60 per cent longer than those of girls.
Longer vocal cords and tracts produce a deeper, more resonant voice pitch.
Testosterone triggers the change in boys at puberty and high levels of testosterone predict deeper voices among adult men.
Recent investigations show that whether women are looking for a short-term or long-term relationship is critical in how they choose among men's voices.
Evolutionary anthropologist David Puts obtained voice recordings of 30 men attempting to persuade a woman to go out on a romantic date.
Then 142 heterosexual women listened to the recordings and rated each man's attractiveness for a short-term sexual encounter and a long-term committed relationship.
Though women said the deeper voices were more attractive in both mating contexts, they dramatically preferred the deeper voices when considering them as prospects for purely sexual, short-term encounters.
Moreover, women in the fertile phase of their ovulation cycle showed the strongest sexual attraction to men with deep voices.
One hint as to why this is so is found in studies of female frogs. They gravitate towards male bullfrogs with deep, resonant croaks, which are a reliable signal - for frogs - of a mate's size and health.
Research on people has revealed two similar reasons that help to explain why women find some men's voices much more attractive than others.
The first involves bilateral body symmetry (when both sides of the body are symmetrical), which is commonly accepted as a sign of good health and good genes.
Body symmetry is also more likely to produce deep voices.
So when a woman finds the resonance of a man's voice even sexier during her fertile, ovulatory phase, she is attracted to the sound of healthy genes for her possible offspring.
SOMETHING IN THE WAY HE MOVES
The way a person dances reveals a huge amount of information.It broadcasts information about age - notice the difference between the
What REALLY makes a woman want to dancing prowess of younger versus older dancers. It also conveys information about energy level, health and biomechanical efficiency.
In fact, in our studies, we found that some women had sex with men simply because they'd been impressed by their dancing. Research reveals that women find certain body movements to be more attractive than others.
One study had women view digitally masked or pixellated images of men dancing. They were more attracted to men who displayed larger and more sweeping movements. They also rated these men more erotic.
Other patterns of men's movements provide women with valuable mating information. Nonreciprocal same-sex touching - when a man touches another man's back, for example - is a well-documented signal of dominance.
Women see 'touchers' as having more status, a key component of a man's mate value. Movements that maximise space, as when a man stretches his arms or extends his legs, are another dominance signal.
Those who display open body positioning - for example, by not folding their arms across the chest - are judged to be more potent and persuasive.
Sexual attraction isn't simply a matter of physical bodies drawn magnetically together in search of compatibility.
For some women, personality - in particular, a good sense of humour - is equally, if not more, important in generating a sexual spark.
One indication of the importance of a good sense of humour in a man is that it is one of the few personality traits that has its own abbreviation in online dating sites: GSOH.
Another is that research shows married women who think their husbands are witty are more satisfied with their marriages than women who do not.
Women rate it as a desirable trait in short-term sexual and long-term romantic relationships.
Why a sense of humour is so important in sexual attraction has been the subject of scientific debate.
One critical distinction is between humour production (making others laugh) and humour appreciation (laughing at others' jokes).
There's a sex difference - men define a woman with a good sense of humour as someone who laughs at their jokes. Men especially like women who are receptive to their humour.
Women, in contrast, are attracted to men who produce humour, and that's true for all types of relationships, from one-night stands to lifelong matings.
The most likely explanation for why women and men alike are attracted to those with a sense of humour is because laughing elicits a positive mood - it's a sign of confidence and intelligence, too.