Why is it that the sight of a certain person across the room can stop us in our tracks and make us weak at the knees, while another person can be in our lives for months or years before we suddenly see them as an object of desire?

And what is desire? What drives us to fixate on the swoop of her shoulder or the turn of his wrists?

Desire is so intangible and unqualifiable. You may be able to define your type, but what makes sparks fly for one human and not another? Why is sexy so subjective?

In a world where there are clear commonly held ideals of what is beautiful, sexy, desirable, why do we fall head over heels in lust with our middle aged boss or the neighbour’s curly haired wife?

Here are a few possible reasons why you’re fantasizing about someone right now.

Physical traits as triggers

We all have certain features that we personally like. Ironically, we grow up aware of our ‘good’ features, and ones we’d rather hide, so often we’re oblivious of why people are attracted to us because what we think is desirable is not what they are looking for.

A friend at school had Elle McPherson legs, with a tiny bust and obsessed over how small her breasts were – while oblivious that her long, slim, gleaming and tanned legs turned heads wherever she went. Guys fell for her lengthy frame and ached for those long limbs to wrap around them, while she worried about padded bras.

My tall dark haired brother is classically handsome with wide shoulders and slim hips, but his wife fell for his sparkly blue eyes and wolfish grin.

Survival of the species

Deeply held within us are the ratios for evolutionary success, and without ever being told what these are we may have an instant recognition that sparks desire when we see the right physical shapes in prospective partners.

Curvy women trigger every evolutionary ‘bone’ in men as they pass with voluptuous bosoms, the ideal hip to waist ratio for childbearing – and even the level of sway in the spine, which has been analysed by scientists to define the perfect level of curvature for successfully bearing the weight of a pregnant belly.

Men’s shoulder to neck ratio predicts their build and strength and their ability to provide for and defend their partner and offspring. Wrists and calves add clues and a tallish height is a less subtle clue that this man will be a strong partner.

Pheromones, baby

Mmmmmmmmm mmm! That scent on your partner’s neck that you can’t get enough of! A healthy person can smell so incredible you’d swear they were wearing perfume or cologne. (And that’s WHY we wear scents, to emulate those naturally alluring pheromones.)

Pheromones really do take sexy to the next level – as well as stimulating sexual arousal and desire, they can influence hormone levels, and even fertility! People with higher pheromone levels tend to have sex more often, feel more confident, and bond more easily with other people – maybe because all these things are easier when everyone thinks you are damn sexy!

Pheromones are not just sex-enhancers though – they are important because they actually help you be attracted to people who are a good genetic match. And pheromones even help ensure that you are attracted to people who are the right sexual orientation for you! In blind ‘sweat-tests’, homosexual men were attracted to other homosexual guys, while hetero men were attracted to the scent of women.

Alone in the dark night

Loneliness is a powerful aphrodisiac! When we are lonely we are more likely to latch onto someone we may have otherwise dismissed, and more likely to obsess over whether we are desired in return.

Often looking back we will wonder what we saw in that person and actually, our desire was ‘not to be alone’.

Thrill of the chase

Ever notice how when you begin to show interest in someone who is pursuing you, they often back off? It’s a lot sexier after the first few encounters to be the one on the prowl, rather than the object of desire. Wondering if you can get the other person to want you can be a real desire furnace, but having someone ‘fall at your feet’ might have the opposite effect.

Our egos are involved in this interplay – we might think that if they want us that badly, they must be less desirable than us, or if they haven’t paid our suit enough attention we might try even harder, partly in order to validate that we are also a worthy prize.

Power play

It’s easy to develop a thrilling crush on people you look up to – professors, bosses, entrepreneurs, teachers, athletes, coaches, heroes – the admiration often sparks into desire and a person who you wouldn’t normally notice takes on a special allure.

Or, desire can spark when you are taking care of someone else, being the hero, receiving the adulation or protecting them. I know a soft hearted man who gets a raging hard on when his partner cries in his arms, because comforting her makes him feel strong and protective, and he found her turning to him very desirable.

A reflection of yourself

Countless studies have analysed which types of person are attracted to each other and whether people are attracted to people like themselves or different. Jung theorized that we seek a union of our conscious and unconscious minds and in order to find this we project elements of our unconscious onto partners and then try to create a union with them in order to complete our ‘self’.

Regardless of the psychology at work, people who share our traits, goals and theories about life can be very desirable – we feel like they really ‘see’ us, because they understand and also hold our point of view. In a way this does make us feel completed.

Our conclusion?

Being self-aware is a super power. Define desire as separate from love, and then check what’s driving your lust for this luminous, alluring, sexy person. Is it desire fueled  by ego, loneliness or by recognition of qualities you admire? Will your desire serve you or hurt you? Will this person be a no holds barred fling, or potential life partner? Regardless of the potential, understanding why you’re holding a candle will help you take care of yourself, and the object of your desire.

If the person you desire is your long term partner, dive in. That’s a beautiful thing.

Thanks to Valeria Smirnova and Jacob Braun for their images.