By Professor Keith Kendrick
Why budding Valentines should look to the animal kingdom for tips on romantic attachment.
Rabbits, deer, dogs, tigers... always at it, if you believe the innuendos.
Humans, on the other hand, are considered more gentle and refined, due to their increased intelligence and heightened emotions.
In fact, when it comes to the key qualities of attraction, humans and animals share more than one might think.
For species with good eyesight, visual displays seem to play a very important role in triggering sexual attraction and hence all forms of visual adornment are used to help attract members of the opposite sex.
It appears that human males are particularly influenced by visual cues from females and of the two sexes tend to fall in love the quickest.
Visual cues: Make-up helps attract the men
Esoteric and surprising visual cues can sometimes be important for some species. Whereas the story goes for humans that gentlemen prefer blondes, lionesses, for example, prefer their males to be deep brunettes.
This is because it is correlated with higher testosterone levels and potentially better genes. For humans and many other primates, faces are the single most important feature for attraction and when we meet individuals a large amount of our visual attention is focused on their face particularly the eyes and mouth.
Considerable attention has focused on the more primitive vomeronasal system in the brain, since this bypasses all the brain's thinking processes and directs its information exclusively towards the regions that control sex and aggression and hormonal regulation.
Male hamsters, for example, have an absolute requirement for this system to be functioning in order to be attracted to and mate with a female hamster.
Male mice also need it to be able to distinguish between males and females and female pigs require it to be turned on by boars.
Smell is more crucial to animals than humans
But in humans, the receptor genes are no longer functioning, so smell does not have the same significance.
We can also detect odours using the main olfactory system which is more complex and gives rise to our conscious experience of smells.
However, while this is an emotive sense it does not have the same potential for "love at first" smell that the vomeronasal system has.
While we don't generally go around tasting each other prior to deciding whether there is sexual attraction or not, there is a lot of taste as well as tactile stimulation going on when we kiss one another, particularly on the lips.
With other animal species there is often much more oral contact between individuals either during social investigation or grooming behaviours.
Like smell it is unlikely for humans that this is the single cue that drives attraction but such oral investigation behaviours must have evolved for a reason.
Kissing is a particularly efficient way for two individuals to be able to sample the chemistry of each other's body, and can give information on health and hormonal status.
Touch is certainly a very good sense for communicating romantic intentions to others and we together with many other species use it quite extensively and often with great subtlety.
The feel of another individual's skin can also tell you a large amount about their health and even hormonal status and memories of caresses received can be extremely poignant.
However, once again for most of us this information is unlikely to be the key trigger for attraction.
Certainly we and many other species find voices attractive and in humans deep, husky ones are considered sexually attractive by both sexes and these correlate with high testosterone levels and therefore potential high sex drive and good genes.
With many bird species a large component of courtship revolves around the complexity of an individual's song but humans are more likely to be the recipient of a professional singer's CD recording, rather than a personal serenade.
True romance established purely by long-distance phone is also something of a rarity and, rather like internet romance, can fall apart when the most important sense finally comes into play - sight.
As with your appearance, you are more likely to be attracted to someone who has a similar personality to yourself, but this is unlikely to stimulate your first feelings of attraction.
However, this is something that females are likely to take more account of than males since females need to be more choosey in picking a mate than their male counterparts do.
We and other animals also seem particularly attracted to others who resemble our parents.
LOVE AT FIRST FRIGHT
Sharing good experiences together might seem a reasonable candidate for success, but research shows it is fear and terror which are more likely to result in mutual attraction.
This is probably because the resultant release of stress hormones activates the brain's neurochemical systems that promote attachment bonds.
This was first shown in a classic study by Dutton and Aron in 1974. An attractive woman interviewed young men on a swaying rope bridge, 200 ft above a river, and also on terra firma.
A deep look into the eyes helps....
Mid-way through the interview, she gives them her phone number. Over 60 % from the rope bridge called her back, versus 30% from terra firma.
Staring deeply into one another's eyes for several minutes also makes us attracted to one another so perhaps the secret of success on a first date is to ride a roller coaster while looking into each other's eyes!
AND IF ALL ELSE FAILS?
If you have not got the key attraction attributes, then hang out with a member of your sex who does have and you may benefit from confusion, frustration or even his or her generosity.
This is a strategy that can be seen in many species which live in social groups although it might not represent a good basis for a long-term relationship.
Professor Keith Kendrick will expand on the theories in this article in a Valentine's Day lecture at Gresham College, London, on Monday at lunch time.