Love, supposedly, is many things.
Blind, if you ask Shakespeare. All you need, says John Lennon. But scientifically compliant? Subject to a set of specified natural laws? Nothing more than a simple mathematical equation? It doesn't sound terribly romantic. Still, it's a prospect that has got matchmakers more than a little excited.
It started with a sweaty T-shirt. Everyone's heard of the infamous T-shirt tests, the one where women are invited to sniff a selection of dirty laundry, and then rank items according to attractiveness. Scientists in Switzerland concluded that we're more likely to favour the smell of partners with dissimilar immune systems from our own, so our offspring have a broader range of immunity.
Across the pond, in California, it was that we liked smells which were similar to our dad's. Combined, the results leave a complex picture of human attraction: we like people who smell different, runs the theory, but not too different. Immune system is important, but so is familiarity.
The idea is that, somehow, attraction comes down to our genes; specifically, the major histocompatibility complex (MHC). Pick a mate whose MHC is too similar to your own, and there is less chance that you will reproduce. Mice can smell too-similar MHC in one another's urine; scientists have speculated as to our ability to taste it in one another's saliva.
Perhaps it's not the most enormous leap, then, to look beyond these initial tests and search for something more. Perhaps it's not surprising – given the number of adult humans looking for love – to find those willing to pass up conventional mating rituals (dinner, a movie, a bottle of red wine) in favour of something a little more scientific-sounding.
Genepartner.com is among several DNA dating websites to have sprung up in recent years. Would-be couples can have their DNA analysed to assess one another's compatibility. The website promises "a successful relationship, a more satisfying sex life and higher fertility rates". And, after all, who doesn't want all that?
It's not just genes. Science has been deployed by the matchmaking industry in all sorts of ways. "Facial analysis" offers similar reassurances, with services such as Find Your FaceMate drawing on a cluster of theories linking physical traits to compatibility. When eHarmony enlisted Oxford University academics to devise more than 200 compatibility-based questions, they claimed to have found the "scientific formula for true love".
And, of course, there are all the other principles we're advised to adhere to, be it a matter of body language (it's all about staring into a date's eyes, concluded one psychologist), environment (experience an adventure together and the adrenaline released will act as a bond), and behaviour (have regular sex to keep feel-good hormones flowing).
But is there any truth in it? The idea that it is possible to boil down romance into a simple, straight-forward formula is understandably attractive. But does it amount to much?
One of Denmark's leading authors on the subject, Lone Frank, examines the question in her book My Beautiful Genome – Exposing our Genetic Future One Quirk at a Time. For all the sweaty T-shirt tests and psychological trials, she remains unconvinced of their relevance to real-life dating. "I've talked to the scientists behind these tests. How much they actually mean to dating is very much up in the air."
Genetics in particular, argues Frank, is susceptible to being misinterpreted. "Suddenly, we can all get our genes looked at, so people emphasise them without taking into account other aspects. Previously, we would have looked at personality, status, interests and so on. There is DNA in everything, so it plays a role in those, but it doesn't dictate them. To say that you can find the person who is scientifically right for you is just not true. If it were that easy, everyone would do it."
Indeed, when it comes down to it, that is largely the point, isn't it? If love were a straightforward case of X + Y, we'd all be happy as Larry. The fact that there's still so many of us out there, floundering about, is testament to the fact that it's not. As a relationship counsellor, Mandy Kloppers sees her fair share of love stories. And regardless of how well-matched individuals may appear, she says, their fate will continue to rest on circumstance. "You can't predict the psychological issues that will come into play."
So what next? Give up seeking the magic answer, the foolproof method of finding The One? Given the money to be made, that seems unlikely; after all, it costs some $249 (around £155) to get your genetic compatibility tested. But perhaps the discerning romantic should turn elsewhere. Perhaps we should leave it up to chance a little more. Love can be found in the most surprising places.
Chance encounters: How we found The One
Peta-Jill Ballenden, with John McDonald for 28 years: "We met in the basement of St Martin's College; I was a sculpture student and he was in health and safety. He was from a Catholic working-class family in the North, I'd had a privileged upbringing in white South Africa. Someone said to me, 'that's an unlikely match'. But here we are."
Barry Hall, in a relationship with Vivienne Hall for 37 years: "One day I drove past the most beautiful girl. I just knew that I wanted to be with her forever. We fell into each other, doing everyday things. I had an old van, so we put a mattress in the back went off on holiday. It was so simple – but it has lasted us."
Alannah Orr, with Eddie Orr for 31 years: "We met at the pub after work and some time later we got together. Then I went home to Australia. On paper, people never would have put us together. We like different books, different music. But he chased me out to Australia, and we got married."