Buttocks are fleshy protuberances at the rear of the pelvis. They occur in many quadruped species, but are common to primates. The human buttocks are composed of the three gluteal muscles (commonly referred to as the glutes), the gluteus maximus, gluteus minimus, and gluteus medius, as well as the fatty tissue that covers them. They are among the strongest muscle groups in the human body, comparable in strength to the thigh muscles. Their general function is to connect the leg muscles to the trunk of the body. In doing so, they provide stability to the core muscles of the trunk, as well as allow for flexibility of the hip muscles and articulated movement of the legs. This muscle group is significant partly because it is separated into two parts by the gluteal crease (the double hemispheres of the buttocks). Thus, this group can work together or allow independent movement of the legs. The gluteal crease is also the location of the anus, which is both the site of excretion of solid waste matter from the body and an erogenous zone. The anus, sphincter, and rectum contain numerous nerve endings, making them sites of potential pleasure and pain. Anal sex, which often involves the insertion of the penis, finger, or an object into the anus, is a common practice, although it is often considered taboo. The rectum shares a muscular wall with the vagina in females and with the prostate gland in males—both sensitive areas that are particularly stimulated by anal intercourse or stimulation.
EVOLUTION AND FUNCTION OF BUTTOCKS
The human buttocks are distinctive among all species in that they are continuously present. The erect stature of humans causes the pelvis to project to the rear of the spinal column, which forces the muscles and fatty tissue of the buttocks into their common configuration. Other species that alternate between an erect stance and walking on all fours have visible buttocks only when their posture allows. Some anthropologists have gone so far as to suggest that the buttocks are responsible for the development of the human brain. The buttocks allow for the upright, two-legged stance distinctive to humans. This stance in turn accommodates two important developments, the freedom of the forearms (previously used for walking on all fours) and the alignment of the spinal column. The use of the arms and hands for tasks other than balance encouraged the development of a complex brain capable of problem solving. Simultaneously the erect stature of humans caused the brain to rest atop the spinal column instead of in front of it, making the frame able to support a larger brain, which in turn was capable of higher-order functions and cognition. There is considerable disagreement about the role the development of buttocks played in initiating the development of the human brain, but it is generally agreed that the unique development of human buttocks was necessary to allow their brain development.
In most primate species, the female buttocks are linked with reproduction. Females signal their readiness to mate by displaying their buttocks, which have become enlarged and swollen. As their menstruation cycle progresses, the swelling becomes more pronounced and, in some species, the color of the buttocks changes to a deep red or purple. After the fertile period of the cycle, the buttocks lose their vivid coloration, and the swelling disappears. The buttocks return to their usual state of being flat and unremarkable. The buttocks of the human female do not change noticeably with the menstrual cycle and have no particular function in the reproductive process. Unlike other primates, the human female is also capable of having intercourse at any time, not just during her menstrual cycle. The configuration of the buttocks and the pelvis orients the human genitalia more to the front of the body than is true in other primates, making face-to-face intercourse possible.
The buttocks contain large amounts of fatty tissue, which gives them their distinct rounded shape. This fatty layer is generally greater in females than in males, which gives the human sexes similar, yet distinct, buttocks and also contributes to the typically wider female hips. This difference in fatty tissue is also apparent in human breasts, which in males are typically lean and flat whereas in women they are fuller and rounder. Anthropologists such as Desmond Morris have linked the development of the human female breasts to the loss of the sexual function of the buttocks. In other mammals, the female breasts are typically flat except when pregnant or nursing. In humans, the female breasts are continuously present, like the buttocks, although they may increase in size during menstruation, pregnancy, or nursing. Morris claims that "the female breasts evolved, quite simply, as buttock mimics" (Morris 1994, p. 122).
The human buttocks became unnecessary for sexual function but remained a site of sexual interest to potential mates. The forward-facing genitalia, however, made the buttocks less apparent, and the breasts developed to resemble the shape of the buttocks and take their place as a visible sexual signal. This is reinforced by the general lack of function of the bulk of human breast tissue. The female breasts are primarily rounded globes of fatty tissue, like the buttocks, and serve little purpose in the manufacture of milk or in aiding breast feeding. Morris further claims that other structures, such as the typically smooth, rounded, facial cheeks typical of female humans similarly mimic the buttocks and are also located in a more prominent, front-facing position.
BUTTOCKS AS AN EROGENOUS ZONE AND IN SEXUAL ACTIVITY
The buttocks have long been an erogenous zone and a source of sexual pleasure and fascination. The shape of the buttocks is pleasing to many and is an often-rendered physical feature in painting and sculpture. As a physical feature common to both men and women, buttocks do not carry the same type of gender-specific taboos typical of the genitals or the female breasts. Because of the excretory function of the anus, however, there is a taboo based in abjection associated with the area. Many people distinguish between the buttocks and the anus, finding one appealing and the other not. Others are stimulated by the taboo associated with the anus as much as by the shape of the buttocks themselves, and take pleasure in both. The popularity of the buttocks as a site of attraction is evident in the proliferation of nicknames for them, including butt, booty, backside, bum, buns, ass, and arse. Fanny is also a nickname for buttocks in American English, but in British English, it is vulgar slang for the female genitals.
In homosexual males, the anus serves as an orifice for intercourse, which makes the buttocks and anus a primary site of sexual activity. Gay men are often divided into groups based upon their preference in anal sexual practice: The receptive partner is called a bottom, while the insertive partner is called a top. Those who enjoy both positions are called switch or versatile. Lesbian anal intercourse is also common, and is usually practiced with a hand-held sex toy (often a dildo) or with the use of a strap-on prosthesis. Because the anus has no natural lubrication, anal intercourse always carries greater potential for tissue rupture than does vaginal intercourse or other sexual activities. It is thus considered a high-risk activity for the transmission of disease, and protection (usually in the form of a condom covering the penis or prosthesis) is usually advised. In cultures where women's virginity is valued highly, (heterosexual) anal intercourse has often substituted for vaginal intercourse as a means of being sexually active while remaining technically virginal. This difference, of course, depends wholly upon the way that virginity is defined. Heterosexual anal intercourse, however, is not strictly a substitute for vaginal intercourse. It is also practiced as a primary form of sexual activity among some couples and as an alternate or occasional activity among others. There are few reliable studies on anal intercourse among heterosexuals, but anecdotal references indicate that it is somewhat common.
The buttocks also figure in sexual practices other than intercourse. Anilingus (also known as rimming) involves one partner licking the anus of the other with their tongue. Massage of the buttocks is common and often a form of foreplay. The buttocks also are involved in a number of fetishistic practices. Clothing designed to reveal, conceal, or accentuate the buttocks is a feature of some fetish activities. Underwear that has been worn and retains the smell of the body parts it covers (including the buttocks) is a primary form of clothing fetishism. This differs from tactile fetishes, which are more concerned with the feel of the clothing item. According to Valerie Steele, "Smelly fetishes may indicate an obsession with bathroom functions, which would seem to imply an 'infantile' perspective on sexuality" (1996, p. 124). Spanking, or striking the buttocks with the hand or an implement of some sort (often a paddle, strap, or whip), is often cited as a common sexual fantasy, although little data exists to demonstrate the degree to which it is actually practiced. Fisting involves the insertion of the entire hand into the anus. It is practiced among heterosexuals, lesbians, and homosexual males, although it is most common to homosexual males. Because the diameter of the human hand and arm (fisting often involves insertion of the arm up to the elbow) is far greater than that of the average human penis or any common sexual prostheses, it involves significant stretching of the sphincter and can be quite painful. It is sometimes incorporated into bondage and discipline/sadomasochism (BDSM) activities or other sexual practices in which inflicting pain or demonstrating dominance over another is desirable.
BUTTOCKS IN HISTORY
The buttocks, particularly of the female, have been the subject of much discussion, fascination, and artistic representation. Some of the earliest examples of human art include carvings of fertility goddesses with extremely ample breasts and buttocks. The most famous example is the Venus of Willendorf, a Paleolithic statuette discovered in Austria in 1908 believed to date back to 24,000–22,000 bce. Buttocks have also famously been depicted in such varying works of art as Donatello's sculpture David (1425–1430) and Paul Cezanne's Large Bathers (1899–1906). Fashion over time has alternately hidden and emphasized the buttocks. The most notable example of the buttocks in fashion is the bustle, popular primarily from 1882 to 1888 in Europe and the United States. This structure (made of fabric but often internally supported by a metal frame) was worn behind the waist, giving its wearer a highly exaggerated silhouette. The effect was meant to be evocative rather than to echo an actual human shape, and while short-lived, it is one of the most recognizable fashion trends in history. Anticipating the bustle was the brief celebrity of Saartjie Baartman, a Khoikhoi woman from South Africa who was brought to Europe and exhibited under the name Hottentot Venus from 1810 to 1815. She was famous primarily for her buttocks, which were enormous by European standards but thought to be typical of her native people. They projected from her pelvis at an angle almost perpendicular to her back and were several times larger than the average buttocks of European women. She was valued both as an oddity and as a representation of ideal female fertility.
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Brian D. Holcomb