From the day we're born, our subconscious starts formulating a "sexual blueprint" that's influenced by everything we hear, see and experience about sex. These blueprints start forming with the feel of a mother's nipple in our mouths and accumulate with both random, "flash" experiences (a two-year-old's glimpse of a neighbour's stocking) and deliberate sexual encounters (our first experience of hands on breasts).
Adding to these blueprints, which become our brains' reference for how we'll feel and think about sex during our lives, is what society presents to us as sexy. Busty page three girls, rangy magazine models with jutting hips and what happens sexually on TV and the movies.
Given that the average Brit watches two hours of TV per day, the sheer volume of celluloid sex we're exposed to makes it dangerously influential. In fact, it's the ability to distinguish between "manufactured" and real sex that can determine just how healthy our sexual blueprints are. Believe too much of it and you end up with a skewed, idealised impression, leaving you feeling dissatisfied with what real life dishes up. Sex never quite matches up to what you expect it to and it never will because it never can. You need to be sexually savvy to recognise the sex you see on TV and the movies isn't even remotely real.
Manufactured sex is a sexual nirvana where everything and everyone is perfect. Real sex is rarely, if ever, perfect. Trouble is, bar walking in on a flatmate or (Ew!) our parents, few of us ever get to see real sex, so our perceptions end up based on the fantasy celluloid model. And even if, intellectually, we know life really isn't like it is on Wisteria Lane and (desperate) housewives don't really shimmy up to their husbands on Monday nights in Agent Provocateur wisps of nothing, heels left on, our silly subconscious isn't quite so clever and easily gets duped. We secretly start to believe that this is what people do and feel less than perfect because we don't.
Everyone always feels like sex as seen on telly, where any and all sexual advances are returned with lusty gusto, erections happen on cue, condoms aren't necessary and he lasts exactly the right amount of time to bring both to earth-shattering orgasms which are always simultaneous and always through penetration. In reality, under 30 per cent of women orgasm through intercourse alone. On screen, simultaneous orgasms are served up more often than hot breakfasts. In the real world, it's romantic to aim for simultaneous orgasms but unrealistic to expect them frequently.
Movie sex sets even higher ideals. Actors are chosen for their perfect bodies and flawless faces, enhanced even further by ingenious makeup and meticulously positioned under flattering lighting. The perfect couple then pout, pose, arch and flex their way through a masterful marathon session leaving us feeling jealous, envious and wondering, "How come my sex isn't like that?" Hollywood sex is artful and seamlessly smooth with not so much as a smudge left on the sheet. Real sex is messy, clumsy, noisy, smelly and sweaty.
It's also dangerous. Neither soap writers nor Hollywood are terribly fond of the seamier side of sex. STDs don't exist on screen. There's not so much as a rustle of a condom, yet we never see the Bond girls doubled up in agony, peeing razor blades, two weeks after James has swept suavely through, or Kim Basinger braving a whopping great penicillin injection nine-and-a-half weeks after having unprotected sex in sewers and kitchens. Which leads some people to believe life really is like a glamorous, exciting action film where people dive under the covers looking fabulous, and emerge, make-up intact, wondrously infection-free and ready for the next love scene. It's not.
We are quick to blame television and Hollywood for glorifying violence, corrupting our young and being the cause of anorexia and body dysmorphia. Yet the entertainment industry is rarely criticised for ruining our perceptions of sex and messing with what should deliver life's most intoxicating moments. Amateur porn is booming and TV bosses, writers and producers should take note. There is something wonderfully reassuring about watching two people have sex who are physically flawed and unscripted. Can we have some of that instead, please?
Tracey Cox is author of 'The Sex Doctor' (Corgi, 7.99).
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