Valentine's Day is all about romance, flowers, chocolates, kisses and Cupid or a last-minute trip to the petrol station for those whove forgotten what day it is.

So surely its nothing to do with cold, logical science?

Wrong, as BBC Focus magazine shows in a special Valentine Q&A about the theory of smooching and other burning issues of the heart...

We all know the story: two pairs of eyes meet across a crowded room and the rest is history. But it turns out there may be some science behind this instant connection. In 2014, researchers asked students to look at a series of photos of attractive strangers while having their eye movements tracked.

When the students reported feeling romantic love , their eyes tended to fix on the strangers face. When it was sexual desire they felt, however, their eyes strayed over the rest of the persons body. In other words, our eye movements can signal whether its love or simply lust that were feeling.

Its not just humans that enjoy a smooch lots of animals have courtship behaviours involving the mouth. Pigeons touch beaks, cats and dogs nuzzle each other, and male fruit flies lick the females.

At the most basic level, kissing is just a way of tasting and touching a potential mate, as part of the process of assessing suitability.

In primates, though, kissing might also be a behaviour that has transferred from maternal feeding.

Kissing is virtually universal in all human cultures, so its possible it is instinctive. But we generally have sex face to face and with our mouths already close together, so its an easy behaviour to stumble upon.

A 1996 study found chocolate caused the release of endorphins in womens brains, making them feel happy. Chocolate does contain a number of compounds associated with mood-lifting chemicals.

But most are present only in small quantities, and some scientists say they are probably almost entirely digested before they reach the brain. It may be the experience of eating chocolate that releases endorphins and happy feelings more than the content of the chocolate itself.

If youre struggling for gift ideas, why not take inspiration from the male red velvet mite? These arachnids will attempt to woo a potential mate by building a love garden an intricate structure of twigs and leaves held together with adhesive sperm. A sperm castle, if you will.

If the female accepts this lovingly crafted sculpture, she will climb on top of it and impregnate herself.

Makes a change from chocolates, anyway

Men tend to seek more short-term relationships and look for physical attractiveness. Women also seek good-looking, short-term mates, but in the long term they are more interested in seeking a man who will provide for them and any children.

There are trade-offs between looks and health, and the desire to find someone similar in education, religion, intelligence, and wanting a family. Few people are aware of these underlying reasons, yet the same effects have been measured in 37 cultures across six continents.

It may flourish when the sun shines. In a 2013 French study, five 20-year-old men set out to ask for womens phone numbers, approaching those in the street who appeared to be aged 18-25. When the sun was shining, 22% of women gave out their numbers, compared with 14% on cloudy days.

Bright sunshine lowers levels of sleep hormone melatonin and increases levels of serotonin in the brain, leading to a better mood. So both the men and women probably felt more cheerful and inclined to take a chance. The temperature was about the same on the different days so it was likely the sun, not the heat, that did the trick.

Unsurprisingly, your photo is key people say they draw more information about someones personality from their photo than their words. A 2016 study found that an open posture is important, so those leaning back or spreading their arms were more likely to receive romantic interest. With the words, stick to a 70:30 ratio of who you are to what youre looking for.

Only some people think they are. In an experiment that manipulated eye colour, women thought brown-eyed and blue-eyed men were equally attractive. And brown-eyed men thought brown-eyed and blue-eyed women were equally attractive. Only blue-eyed men preferred blue-eyed women.

This may seem odd but there could be a simple evolutionary reason. Blue eye colour behaves like a recessive trait. This means that to have blue eyes you must have inherited two copies of the genes from your parents. So if a blue-eyed man has children with a blue-eyed woman and one of the children has brown eyes, he knows it cannot be his own.

Alas no, so put that love potion on hold. Although chemicals play an important part in mediating our emotional response, the interaction of various hormones with our current state of mind and memories is much too complicated to be captured in a simple formula. If you inject someone with adrenaline, they may feel the physiological sensation of anxiety, but whether this translates to the emotion of fear, anger or sexual arousal will depend on the circumstances.

Most people cant focus on anything as close as a face at kissing distance so closing your eyes saves you from looking at a distracting blur, or from the strain of trying to focus.

Kissing can also make us feel vulnerable or self-conscious and closing your eyes is a way of making yourself more relaxed. Its like turning out the light before having sex, but in miniature.

Excerpt from:
Think you have chemistry? The cold science behind Valentine's Day romance - Mirror.co.uk