It strikes me how often people forget of their biological roots and assign 'higher' motifs to their behavior. In this article I would like to look at some explanations for common human preferences towards members of the opposite sex. The list, sometimes speculative, nonetheless revealing some plausible motifs, is intended to highlight the evolutionary reasons hard-coded in our brains.

It is not difficult to notice which features of the human female have most immediate impact on the human male. I have selected those that can be attributed realistic explanation (encountered in popular and scientific literature).

FEMALE

- body shape, in particular the ratio between waist and hip circumference. The ratio (not so much the absolute measures!) have been found to correlate with levels of female hormones warranting fertility. Once a medical friend of mine said: wide hip is what men should look for - it is crucial for problem-free delivery. Well, perhaps not in the days of the caesarian cut, but still... In addition, as pregnancy increases the circumstance of the waist without changing much that at hip level, searching for pleasantly 'curved' women can be quite naturally attributed to their reproductive readiness.

- hips and tights, with those rounded bringing more attention. Here the explanation could be awarded to the fact that a woman will ovulate only if her body has stored some fat (more than 20% of body weight) and tights and hip are the female 'storage' area. This distribution of fat provides also an easy check for hormonal abnormalities - too much, too little, not in the right place may suggest that something is going wrong with her fertility as well.

Men also seem to express taste for long legs - I have not come across any reason for that. A more general explanation could be with tallness (with much of the extra growth coming from the legs) viewed as a measure of overall well-being during the growth period (more about this in the section devoted to big men).

Women seem to be well aware of the importance of being 'in shape'. In older times, the corset tightening the waist constituting the main tool extended today to exercise routines (aerobics, calanetics etc.) aimed at mid-body muscles (unlike male weight lifting promoting chest and upper body muscle growth - more about this later). A psychologist friend of mine once mentioned her observation of women spending more time in the gym prior to breaking a relationship or while single, up to the point of finding a new partner.

- breast size, with preference given to bigger breasts. Though not strictly true, bigger breast potentially indicate greater ability to breast-feed children, so important to their health and well being even today in the times of milk formulas. In older days when mother's milk was the only alternative available, its lack was fatal to the child' survival. Also, breasts consisting mostly of fat tissue indicate woman's 'stores' - again crucial (for her and any newborns) in the times of common famine.

Female breasts are not fully developed until the first pregnancy, usually enlarging their size. Thus the tendency towards bigger breasts could also be attributed towards women who have already 'proven' their fertility. No surprise then that most of the prehistoric fertility goddesses are pictured as big-breasted and round shaped. According to some theories, men are conditioned to rounded shapes resembling another part of the human body, with the breasts mimicking it (D.Morris).

Again, modern women exploit this male preference by using bra designed to lift, shape, expose and often enlarge this organ, one could think mostly for (diminishing!) feeding of the newborn. Various treatments, including silicone implants, have been also invented with the sole purpose of enlargement. And breast removing surgery, despite being non-life threatening, is often causing great psychological trauma due to loosing this so important indicator of one's sexuality.

- face, it is difficult to describe what constitutes a pleasantly looking face, however amongst the many possible descriptions some common features emerge: regularity, shiny eyes, healthy skin and teeth. Face is one of the body parts people pay most attention to. Why? Because even in the case of non-verbal communication so much can be read from face only. Here are some of the features:

- 'genetic' health - the more regular face the less distortion in the working of genes - only perfect coordination leads to symmetry and regularity

- health, nutrition - skin: sensitive indicator of general health, healthy (white) teeth - no calcium deficiency

- hormonal balance - no facial hair, voluptuous lips

- vitality - visible through eyes (movement), vivid mimic, head movements

- muscularity - physical activity often tenses facial muscles leaving its mark on them

- attitude - smiling and being relaxed shapes the facial expression thus allows to recognize those attitudes, similarly as anger or tension

- personal interest - best expressed by eyes: longer gaze, pupil dilation

- interest - turning head to the side, looking intensively

- emotions - reddish chicks, eyelid movement, tears, more than 40 facial muscle at work

- confusion - involuntarily hand movements towards the face, (covering for) coughing, eye contact avoidance

- habits - smoking: gray skin & teeth, drinking: red nose, undersleeping: small, black-ringed eyes

- age - no part of the body tells it better than skin on the neck and around eyes; also younger faces are rounder

- intellect - somehow expressible through eye movement, facial expression, but this can be grossly misleading

- wealth - can be indicated by additions: ear-rings, necklace, clasps

What's the modern way to deal with this mirror of the body and soul? Dark glasses, (color) make-up, lipstick, (fake) jewelry and other treatments mentioned elsewhere allow to change the normal facial expression beyond recognition (sometimes literally).

- age, physically grown up, but otherwise young female seems to be the desired case. So why is this? The explanation could be again: fertility, is much higher among young women as well as the probability of delivering a healthy baby. The preference for younger women is quite strong, maybe because they exhibit many of the other desired features.

I have talked to a number of men (around 30 years old) about this. Though many admit that younger girls are boring in the longer run due to immaturity, many a man find them irresistibly attractive, at least at 'the first sight'. This preference for purely biological features over those 'socially acquainted', such as maturity, education, emotional stability, material position etc. for me constitute an important indication of the force of 'primitive' drives over our acclaimed reason-based behavior.

So what do women do? First they do not exclude their age - this is one of the 'taboos' of our times. Second, by the use of cosmetics, plastic surgery etc. they try to look younger and do not mind at all being mistaken for younger than they actually are.

- skin, delicate, lightly rosy, with no pimps and other unusual features. Skin, the most external tissue, thus unlike others exposed to inspection, can be viewed as a barometer of the overall well being. Sensitive to malnutrition, smoking, tiredness, age, skin, even to an untrained eye, delivers a message about the owner's condition. For example exceedingly white may indicate anemia (common among menstruating women - so rosy shade is preferred?), gray - smoking, with pimps - problems with digestion, one of many illnesses, hormonal instability, wrinkled - tough life style, age.

What's the female response to this tale then? Make-ups, cosmetics, treatments vitalizing, nourishing, regrowing (facial) skin, just to mention few.

- hands (and feet), 'unworn'. I would take this preference as an indication towards people of higher status who could afford avoiding extensive manual work (or walks in primitive foot coverage).

Modern improvements in this area include manicure, pedicure use of gloves, possibly painting of nails.

- hair, strong, dense, 'full'. Hair seems to be an important indicator of one's sexuality and state. Even modern, often short-haired, women express a peculiar reflex of presenting their hair (making it visible via head movement and reaching to it with the hand) in the presence of an interesting male. I do not know what's the motivation - only mention here that hair, similarly to the skin, is quite sensitive to improper nutrition and illnesses wearing down the body. Facial and bodily hair, apart from pubic and in the pits, in the case of females most likely indicate hormonal imbalance, while the growth of hair in the two other areas accompanies reproductive maturity.

So what's the response? Again inventiveness is quite genuine: from hair thickening, nourishing, styling products to colors and extra hair implants. Unwanted hair, gets harsh treatment as an abnormality.

- smell. I will not even attempt to describe 'the desired' scent of a woman partially because ... it is not consciously realized by men. In an experiment men were asked to sniff tissue soaked in female vaginal fluids during different stages of ovulatory cycle. Though the men could not tell the difference their testosterone level rose while smelling samples from ovulating (i.e., being able to conceive) women.

Since higher level of testosterone induce higher sexual drive and aggressiveness, the explanation for the raise could be that men in the presence of a fertile woman behave more aggressively to get rid of the rivals/protect the female and are more inclined to have a sexual interaction with her - everything without knowing why they behave like this! The recent re-discovery of the vermonasal organ selectively sensitive to, among others, smell of skin of the opposite sex could shed a lot more light on the behavior.

So what starts happening in relation to this? A new generation of 'sexually loaded' perfumes is already on sale. Well, let's smell.

Another reported female tendency includes increased infidelity during ovulation. Explanation could be of at least two types: possibly women feel increased sexual drive during this part of their cycle so naturally look for more common encounters outside the usual setting, yet another explanation could be that this is drive specifically aimed at getting conceived by a male more attractive (~ genetically fit) than the common partner reserved for providing stability.

Since a child mostly resembles his father between the ages of 1 and 2 years (to give him a boost in taking care?) but only to a limited extend, he will never know anyway, well, would not know in the times preceding genetic tests.

MALE

- tallness. Tall males create the impression of being more care-taking and probably increasing sense of security. As the latter is easy to understand: taller so probably better runner, hunter, fighter, so better provider, there is another aspect of size - growth is one of the most universal measures of overall inbred fitness of an individual, both inherited and acquired mostly in adolescence. Everything gets noted: poor nutrition, stress, frequent illnesses, pollution, addictions - all decrease tallness with males around 190cm statistically living longest (height bigger than that usual results form some growth abnormalities).

So what do men do to present this feature. If they need, shoes on (hidden) heels and risen hair seem to be some solution.

- muscular so presumably strong and fit (as muscles do not appear without using them) - so important characteristics in times when physical fitness was required in almost any activity, including those most important for survival: getting food and defending oneself/relatives.

Times changed, but female perceptions did not, so (some) males invest lots of time and effort in getting a muscular physique. One of the arguments that the muscle size - not the actual strength, endurance etc. - is what matters could be highlighted by the training regime, aimed at (and often measured by) the visual muscle growth and particularly concentrating on highly exposed parts of the body: chest, upper arm etc.

- wealth used to be quite easy to asses: by the size of travel arrangements, or of the house, the number of flocks in one's herd, or servants in the household. Now, with the advert of money it is not that visible, but still equally important with females (strongly) preferring richer guys. So what do the guys do. An expensive car, sporty or big, will do to indicate one's status. Smart, business-like clothes - presumably showing belonging to a certain class - are also in demand as well as the allowed male valuables: prominent watch, perhaps a golden ring, chain and even spectacles' bindings.

- romantic and caring, presumably in relation to the female and their progeny. As the preference for caring and providing males seems to be quite understable in circumstances when the male was really needed to provide for the child-bearing female, the requirement for being romantic is not that obvious. One way of viewing a romantic feeling towards someone is as involuntary affiliation to that person, not based on any singular feature but on the overall impression. As such romanticism on the male side could be seen as a safeguard against leaving a female (and their offspring) when a major attractiveness, e.g. physical beauty, disappears.

So how do men cope. In order to overcome the female reluctance, men go through a number of steps increasing the romantic feel and, finally, intimacy of an encounter. After the initial interest expressing glaze and more or less spontaneous exchange, only those who will be able to relate to a woman in a caring and personal way can expect to survive the selection. This is achieved, among others by, referring by name, touch, compliments, close and open position, signs of listening and understanding, so visible in skillful men.

- prominent jaws (and cheekbones) are other physical feature contributing towards male attractiveness. Why? Potentially because of their visible growth during adolescence being easily disrupted by any malfunction at that important time. So no problem with bone growth - no problem in other aspects of life at the basis of someone's adult existence. A good sign for a potential mate.

- creative, intelligent men seem to attract more interest perhaps because as such they are more likely to deal successfully with problems posed by life (and perhaps make more creative lovers?)

- bad smell and poor hygiene is a strong anti-aphrodisiac for women. So why is it stronger than in the case of men. Perhaps because genital infection can have more serious consequences for woman's fertility than that of a man. On the other hand, in an experiment where women were asked to evaluate their desire for a man on the single basis of the smell of his T-shirt, the preference was simple: greater for genetically unrelated men when the female was not pregnant and for relatives otherwise. The explanation might be simple: varied parental genetic make up contributes towards more fit offspring whereas, in the times of pregnancy, it pays better to be among relatives.

- shapely bottom, o yes, seems to cause almost the same emotions in both sexes. I have not come across any explanation of this phenomenon, perhaps the closeness of the reproductive organs is the primary interest reason.

- big penis really distinguishes humans from the rest of the animal world, namely human males have the biggest penises in relation to body size among all primates! Apparently there must be an evolutionary advantage in that. What it might be? One explanation could be that big penis increases chances of conception either by exiting more the female partner, thus potentially increasing likelihood of successful sexual encounter, or just by improving penetration and sperm delivery.

Once I witnessed a female discussion's consensus that a man should be rich and ugly. As already pointed, the richness-wealth part is understable, but why ugly? I do not feel in position to invent the argument, however would like to draw to attention the fact that testosterone, the male hormone, suppresses the immune system thus making highly potent males more prone to infections. Is therefore this kind of ugliness, resulting from skin, early childhood infections etc., what is sought for? I doubt it, since it could be just a result of a weak (so undesired) immune system, but maybe there are more subtle distinctions. Another explanation could be more sociological: a male partner unattractive in the quick - visual judgment by other females may be actually desirable as promoting a more stable relation.

COMMONITIES

In addition to the features discussed separately above, there are, some common turn-ons:

- flat stomach - perhaps a modern desirable - in the age of common obesity this feature can be considered as a sign of 'sporty' so perhaps wealthy life-style additionally enforced by the fact that non fattening diet is usually more expensive.

- long fingers - expression of manual ability?

- prominent cheek (and to some extent chin) bones - as already discussed in the case for men. Liposuction (in the US) is most common on cheeks. Why? To make the cheekbones more visible?

- muscular body - seems to be desired not just on the male side. Another sign of healthy life style, non-obesity etc?

- body symmetry - in a controversial study more symmetrical men had their first sexual contact up to 2 years earlier than their not-so-equally-drafted peers, women had more orgasms while having sex with highly symmetrical partners etc.

- tall forehead - perhaps due to some diseases causing mental impairment also causing skull deformation.

So are we really so 'above the animals' as some people claim?

Literature

Desmond Morris. The Naked Ape: A Zoologist's Study of the Human Animal
Desmond Morris. Intimate Behavior: A Zoologist's Classic Study of Human Intimacy
Matt Ridley. The Red Queen: Sex and the Evolution of Human Nature
David M. Buss. The Evolution of Desire: Strategies of Human Mating
Various articles, New Scientist