Sexual attraction

Sexual attraction, in species which reproduce sexually, is attraction to other members of the same species for sexual or erotic activity. This type of attraction is often important for the survival of sexually reproducing species, while in many species serves no immediate reproductive goal.

Sexual attraction in animals
Sexual attractiveness in non-human animals depends on a wide variety of factors. Often, there is some element of the animal's body which exists for sexual attraction, like the bright plumage and crests of some species of birds. In many species, there are behaviours which appear to be sexual display. Some of these attributes seem to exist solely to demonstrate fitness and health, for example by demonstrating the ability to sustain an "expensive" feature with no other apparent survival function. Conversely, the receiving sex may be predisposed to perceive these features as sexual attraction. It is possible that these features by the giving or the receiving ends cause major survival problems (see game theory), especially where, as in moose, a direct competitive element is involved.

Frequently (especially in insects) chemical signals are used to generate sexual interest and to locate potential mates. These signals, known as pheromones, can produce a profound effect upon an animal's behaviour even when present in very minute quantities.

Common elements of sexual attraction in humans
Typically, sexual attraction refers to a person being drawn to another in order to have a sexual relationship. The concrete meaning of a sexual relationship differs across cultures and history. Because human social behavior is often highly complex, a sexual relationship may entail one which, at its beginning, has little or no sexual behavior, and only after a period of time, which can be a courtship period, or a threshold such as marriage, does sexual activity enter the interaction patterns.

Certain aspects of what is sexually attractive is universally agreed upon across the human species, or nearly universal among particular cultures or regions, while other factors are determined more locally, among sub-cultures, or simply to the preferences of the individual, which may come about as a result of a variety of genetic and psychological factors. Sexual attractiveness of a person to another person depends on both persons;

Much of human sexual attractiveness is governed by physical attractiveness. This involves the senses, in the beginning especially:
 * Visual perception (how the other looks)
 * audition (how the other sounds (in their voice and movements))
 * Olfaction (how the other smells, naturally or artificially; the wrong smell may be repulsive).

Some studies suggest that one source of physical attraction of a human male to a human female is dependent upon a proportion between the width of the hips and the width of the waist (aka waist-hip ratio) (see Golden ratio).

As with other animals, pheromones may also enter into the picture, though less significantly than in the case of other animals. Theoretically, the "wrong" pheromone smell may cause someone to be disliked, even when they would otherwise appear attractive. Frequently a pleasant smelling perfume is used to encourage the member of the opposite sex to more deeply inhale the air surrounding its wearer, increasing the probability that the pheromones from the individual will also be inhaled. The importance of pheromones in human relationships is probably limited and widely disputed, although it appears to have some scientific basis.

A sexually attractive visual appearance in humans generally involves:
 * a general body shape and appearance sanctioned by the local culture.
 * a lack of visible disease or deformity.
 * a high degree of mirror symmetry between the left and right sides of the body, particularly of the face.
 * pleasing bodily posture.

However, these factors are complicated by many other factors. There may sometimes be a focus on particular features of the body, such as breasts, legs, hair, or musculature.

Factors determining sexual attraction to human females
A youthful, or neotenic, appearance is a notable factor governing the degree to which a female individual is regarded as sexually attractive.

In Western societies, various cultural features may reflect the preference for neotenic female partners; many are dated to antiquity. These include depilatory practices (acomoclitism: intentional hair removal for visual and other effects) and a preference for light or blonde hair.

A strong aspect to sexual attraction is proportion. It is typical for a plastic surgeon to correct a perceived error of proportion, such as making a nose that is too big smaller via rhinoplasty, or making breasts larger via breast implants.

One idea of physical beauty regarding the breasts of women is that the best shape approaches the shape of a three dimensional parabola (which is called a Paraboloid of revolution) as opposed to a hyperbola, or a sphere. Conversely, the shape of the buttocks of an attractive person (male or female) tends to resemble the shape of a cardioid, which is the inverse transform of a parabola.

In regard to the female genitalia, the aesthetic consensus stresses the roundness and largeness of the labia majora, and the symmetry of the labia minora. Vulval aesthetics are relatively new in being observed, as previously the female genitalia was regarded as either repulsive, uninteresting, nonexistent, or taboo in Western culture. The realization to the contrary following the feminist movement and sexual revolution has brought about a new realm of plastic surgery and so-called designer vaginas.

The appearance of health also plays a part in physical attraction. Often, women with long hair are thought to appear more beautiful, as the ability to grow long, healthy looking hair is an indication of continuous health of an individual. Another indication of health of an individual is the ability to grow long, strong, healthy-looking fingernails. The preference for this effect has resulted in the fact that artificial nails and manicures have grown extensively popular for women beginning in the 20th century. Toenails also feature as a component of sexual attractiveness to some degree. Healthy-looking skin is also considered a beauty trait.

Weight, whether tending toward thinner or heavier, has sometimes been considered a physical factor governing attractiveness of both genders (typically women), but there is some debate suggesting that this is actually a social factor indicating desirability. In some cultures, both historically and in the present day, a female with greater than average weight has been seen as sexually attractive. However, this cannot be solely because fat deposits provide the energy needed for developing a healthy fetus, as in other cultures, women so thin as to stand a high risk of miscarriage are considered attractive. Rather, weight is a visible indicator of social status and wealth; in some societies, only the rich can afford to be fat, while in others, only the rich can afford liposuction and personal trainers, or have meaningful employment that promotes healthy diet and exercise habits. Therefore weight is at least partially an indicator of social status, which is itself sexually desirable to many. It may also merely be that, as it is unhealthy to be too fat, this can be seen as unattractive.

Factors determining sexual attraction to human males
It is thought that sexual attraction to a man by a woman, is somewhat determined by the height of the man. For the woman, the man should be at least a few percent taller than her in order to be perceived as handsome. In European populations the average height of males is about 175 cm whereas the average height of females is about 165 cm - a 6% difference. It would be preferable if the man is at least a little above the average in height in the given population of males.

Among heterosexuals, the initial attraction usually begins with the physical features of the human form and attire.

Those who believe that the muscular contour of a male is attractive, will choose other males with well-defined muscles. Males who make use of their hormone testosterone through exercise or bodybuilding techniques find themselves attractive as their muscles take shape.

At various times in history and throughout various cultures and sub-cultures the growth, maintenance and display of facial or body hair produced as a by-product of testosterone activity within male bodies has been considered a primary characteristic of sexual attractiveness, and of a display of masculinity in general. Cultural development seems to oscillate through multi-generational cycles from one pole to another: extreme hair growth, especially of facial hair accompanied by elaborate grooming rituals is often followed within a couple of generations by a widespread antipathy to body hair and the widespread adoption of depilatory practices.

The causal mechanism for this oscillation has not been established but differences in the simultaneous characterisation of body hair attractiveness within a culture between different social classes may indicate that the dynamic force driving the diffusion of differing male body hair social practices is in fact mate selection by females.

Other aspects
Many people exhibit high levels of sexual fetishism, and are sexually aroused by other stimuli not normally associated with sexual arousal. The degree to which such fetishism exists or has existed in different cultures is controversial.

Often the result of a sexual attraction is sexual arousal.