I’m in Liverpool for the BA Festival of Science, and tonight went to a lecture by Richard Robinson called Why The One You Fancy Never Fancies You.

It was entertaining, although I could probably have been more interested if I didn’t immediately turn sceptical when he started the talk by asking how we fall in love with someone the moment we see them.

Actually, it turns out, there are two hormones responsible for making you “fall in love” with someone: PEA, or Phenylethylamine (try saying that three times fast) and serotonin. The former is controlled by the pituitary gland and when you see someone you fancy, PEA goes whizzing around your body. At the same time, your serotonin levels drop. As serotonin (commonly known as the hormone that makes you happy) controls rationality, you become obsessive about the person you just spotted.

Now, I said I was sceptical. I meant it. I can’t quite get my head around this idea that a couple of chemicals whizzing around your body (or not, in the case of serotonin) can make you fall in love with somebody you’ve never even spoken to.
I’m trying to deal with this by telling myself that actually, these hormones make you fall in lust, and if that works out, you fall in love with all the things you like about the person you saw at that party, but I’m no scientist, so I could be wrong.

So, now we know why we fall for people. How do we attract the people we fall for? (This is where it gets amusing.)

• peahens are attracted to cocks (stop giggling at the back) with the least parasites, and they choose the cock with the nicest tail feathers. We are like peacocks: we choose a mate with nice hair. (Cynical bit: I could have told you that ages ago - long, soft strokable hair has been a pet love of mine for years - I love stroking hair almost as much as I love having my own stroked!)
• In history, primitives had piercings and stretched skin. It’s believed that they did this to show how big and strong they were to those they were attracted to - and yes, we get piercings too. (For what it’s worth, I’m not trying to look big and strong; I just think piercings are hot.)
• The women of the Padaung Tribe in Thailand wear rings around their necks, which painfully push their clavicle down and give the appearance of a lengthened neck. We just wear high heels.

What do the people whose attention we’re trying to attract do when they see a pierced, stiletto wearing person with nice hair? First, they focus their attention on something. They look at that tiny detail, and decide if they fancy the person or not. They then use cognitive miserliness and naïvely make further decisions about what a person might be like in order to decide whether or not they could be attracted to them further based on stereotypes (”well, they have nice hair, but they’re blonde, so they’re probably stupid too”).

For what it’s worth, statisticians have detemined that we’re attracted to people who are similar to us in various ways, including age (Er, yes. Not that I like breaking stereotypes or anything.), religion, political views, interests, location (Hmm. Not sure about that either.), IQ, wrist sizes, ear lobe sizes, middle finger length and lung capacity. (This tells us that statisticians need to get out more.)

So, you’ve worked out that you fancy someone. Why don’t they fancy you? (Now it actually gets interesting.)

We’ve all heard of pheromones - you know, a chemical that passes messages from one organism to another. One particular pheromone, Major Histo-Compatibility Complex, is responsible for whether or not people fancy us. It works a bit like a barcode - a potential partner’s white blood cells detect MHCC and they note how similar it is to the host body’s MHCC pheromone. If it’s too similar, we don’t fancy each other. This, theoretically, means that incest doesn’t happen, but even science gets it wrong sometimes. Simply put, if my MHCC smells like, oh, chocolate, and so does yours, I won’t fancy you… but if you smell like vanilla, I will.
This was proven by getting six girls to wear a brand new shirt two consecutive nights, and then putting each shirt in a jar. Scientists then get a guy to sniff each of the jars and rate them on a scale of 0 to 6. When they tested the MHCC of each of the participants, it was found that the girl rated highest had the most different MHCC, and the girls rated lower were more similar to him.

So. How do you find the one you fancy? Simple. Sniff them. (If you like it, and they don’t run away screaming, you know you’re onto a winner.)