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96-562: In other mammals , the labia majora are not present and the labia minora are instead referred to as the labia vulvae . Labium (plural labia ) is a Latin -derived term meaning " lip ". Labium and its derivatives (including labial, labrum) are used to describe any lip-like structure, but in the English language, labia often specifically refers to parts of the vulva. The labia majora are lip-like structures consisting mostly of skin and adipose (fatty) tissue, which extend on either side of

192-406: A classroom or living room. During puberty, if not before, the tip and opening of a male's foreskin becomes wider, progressively allowing for retraction down the shaft of the penis and behind the glans , which ultimately should be possible without pain or difficulty. The membrane that bonds the inner surface of the foreskin with the glans disintegrates and releases the foreskin to separate from

288-405: A core of erectile tissue . The color, size, length, and shape of the inner labia can vary extensively from woman to woman. In some women, the labia minora are almost non-existent, and in others, they can be fleshy and protuberant. They can range in color from a light pink to brownish black, and texturally can vary between smooth and very rugose. The urogenital folds form the labia minora while

384-462: A delay in the onset of puberty past the age 14 in females and 15 in males is Kallmann syndrome , a form of hypogonadotropic hypogonadism (HH). Kallmann syndrome is also associated with a lack of sense of smell ( anosmia ). Kallmann syndrome and other forms of HH affect both men and women. It is caused by a failure in HPG axis at puberty which results in low or zero gonadotropin ( LH and FSH ) levels with

480-520: A gynecologist, or perform a genital self-examination. Developing an awareness for how much the labia truly differ between individuals may help to overcome this self-consciousness. In several countries in Africa and Asia, the vulva is routinely altered or removed for reasons related to ideas about tradition, purity, hygiene and aesthetics. Known as female genital mutilation , the procedures include clitoridectomy and so-called " pharaonic circumcision ," whereby

576-885: A major role in the Neolithic Revolution , and resulted in farming replacing hunting and gathering as the primary source of food for humans. This led to a major restructuring of human societies from nomadic to sedentary, with more co-operation among larger and larger groups, and ultimately the development of the first civilizations . Domesticated mammals provided, and continue to provide, power for transport and agriculture, as well as food ( meat and dairy products ), fur , and leather . Mammals are also hunted and raced for sport, kept as pets and working animals of various types, and are used as model organisms in science. Mammals have been depicted in art since Paleolithic times, and appear in literature, film, mythology, and religion. Decline in numbers and extinction of many mammals

672-542: A male reaches his teenage years, erections occur much more frequently due to puberty. Erections can occur spontaneously at any time of day, and if clothed may cause a bulge or "hump". This can be disguised or hidden by wearing close-fitting underwear, a long shirt and baggier clothes. Erections are common for male prepubescent children and infants, and can even occur before birth. Spontaneous erections, also known as involuntary or unwanted erections, are normal. Such erections can be embarrassing if they happen in public, such as

768-440: A male's first ejaculation occurs at age 13. Ejaculation sometimes occurs during sleep; this phenomenon is known as a nocturnal emission . In males, testicular enlargement is the first physical manifestation of puberty (and is termed gonadarche ). Testes in prepubertal males change little in size from about 1 year of age to the onset of puberty, averaging about 2–3 cm in length and about 1.5–2 cm in width. The size of

864-438: A more developed body may also result in the refusal to undress for gym. These experiences lead to lower self-esteem, more depression and poorer body image in these early-maturing females. Furthermore, as physical and emotional differences set them apart from people in their same age group, early-maturing females develop relationships with older people. For instance, some early-maturing females have older malefriends, "attracted to

960-434: A period of sexual stimulation, the labia minora will become further engorged with blood approximately 30 seconds to 3 minutes before orgasm, causing them to redden further. In those who have had children, the labia majora may also swell significantly during this period, becoming dark red. Continued stimulation can result in an orgasm, and the orgasmic contractions help remove blood trapped in the inner and outer labia, as well as

1056-400: A skin condition that is characteristic of puberty. Acne varies greatly in its severity. Testosterone will cause an enlargement of the clitoris and possibly has important effects on the growth and maturation of the vestibular bulbs , corpora cavernosa of the clitoris and urethral sponge . Changes of the vulva initiated by estradiol as well as its direct effects also appear to influence

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1152-785: Is menarche , the onset of menstruation, which occurs on average around age 12½. For males, first ejaculation , spermarche , occurs on average at age 13. In the 21st century, the average age at which children, especially females, reach specific markers of puberty is lower compared to the 19th century, when it was 15 for females and 17 for males (with age at first periods for females and voice-breaks for males being used as examples). This can be due to any number of factors, including improved nutrition resulting in rapid body growth, increased weight and fat deposition, or exposure to endocrine disruptors such as xenoestrogens , which can at times be due to food consumption or other environmental factors. However, more modern archeological research suggests that

1248-419: Is a chemical used to make plastics, and is frequently used to make baby bottles, water bottles, sports equipment, medical devices, and as a coating in food and beverage cans. Scientists are concerned about BPA's behavioral effects on fetuses, infants, and children at current exposure levels because it can affect the prostate gland, mammary gland, and lead to early puberty in females. BPA mimics and interferes with

1344-425: Is a wide range of normal ages, females typically begin the process of puberty around age 10½ and end puberty around 15–17; males begin around ages 11½—12 and end around 16–17. Females attain reproductive maturity about four years after the first physical changes of puberty appear. In contrast, males accelerate more slowly but continue to grow for about six years after the first visible pubertal changes. For males,

1440-408: Is above the perineum and below the frenulum of the labia minora . The grooves between the labia majora and labia minora are known as the interlabial sulci or interlabial folds. The labia minora are two soft folds of fat-free, hairless skin between the labia majora. They enclose and protect the vulvar vestibule, urethra and vagina. The upper portion of each of the labia minora splits to join both

1536-552: Is achieved at an average age of 15 years for an average female and 18 years for an average male. Potential fertility (sometimes termed nubility ) usually precedes completion of growth by 1–2 years in females and 3–4 years in males. Stage 5 typically represents maximal gonadal growth and adult hormone levels. The definition of the onset of puberty may depend on perspective (e.g., hormonal versus physical) and purpose (establishing population normal standards, clinical care of early or late pubescent individuals, etc.). A common definition for

1632-462: Is considerably more complicated than in males. The main steroid hormones , testosterone, estradiol, and progesterone as well as prolactin play important physiological functions in puberty. The production of gonadal steroids in females starts with production of testosterone, which is typically quickly converted to estradiol inside the ovaries. However the rate of conversion from testosterone to estradiol (driven by FSH/LH balance) during early puberty

1728-420: Is considered a sign of fertility, leading some women to have pubic hair transplants. Some women are self-conscious about the size, color or asymmetry of their labia. Viewing pornography may influence a woman's view of her genitals. Models in pornography frequently have small or non-existent labia minora, and images are often airbrushed, so pornographic images do not depict the full range of natural variations of

1824-463: Is for African-American females and the latest average onset for high altitude subsistence populations in Asia. However, much of the higher age averages reflect nutritional limitations more than genetic differences and can change within a few generations with a substantial change in diet. The median age of menarche for a population may be an index of the proportion of undernourished females in the population, and

1920-464: Is highly individual, resulting in very diverse development patterns of secondary sexual characteristics . Production of progesterone in the ovaries begins with the development of ovulatory cycles in females (during the lutheal phase of the cycle), before puberty low levels of progesterone are produced in the adrenal glands of both males and females. Estradiol levels rise earlier and reach higher levels in women than in men. While estradiol promotes growth of

2016-493: Is more likely to leach out of plastic when its temperature is increased, as when one warms a baby bottle or warms up food in the microwave. Nutritional factors are the strongest and most obvious environmental factors affecting timing of puberty. Scientific researchers have linked early obesity with an earlier onset of puberty in females. They have cited obesity as a cause of breast development before nine years and menarche before twelve years. Early puberty in females can be

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2112-466: Is normal. In Canada , the average age of menarche is 12.72, and in the United Kingdom it is 12.9. The time between menstrual periods (menses) is not always regular in the first two years after menarche. Ovulation is necessary for fertility , but may or may not accompany the earliest menses. In postmenarchal females, about 80% of the cycles were anovulatory in the first year after menarche, 50% in

2208-418: Is often the second noticeable change in puberty, usually within a few months of thelarche. It is referred to as pubarche . The pubic hairs are usually visible first along the labia . The first few hairs are described as Tanner stage 2. Stage 3 is usually reached within another 6–12 months, when the hairs are too numerous to count and appear on the pubic mound as well. By stage 4, the pubic hairs densely fill

2304-572: Is primarily driven by human poaching and habitat destruction , primarily deforestation . Over 70% of mammal species are in the orders Rodentia , Chiroptera , and Eulipotyphla . Mammal classification has been through several revisions since Carl Linnaeus initially defined the class, and at present , no classification system is universally accepted. McKenna & Bell (1997) and Wilson & Reeder (2005) provide useful recent compendiums. Simpson (1945) provides systematics of mammal origins and relationships that had been taught universally until

2400-477: Is the Vandenbergh effect ; a juvenile female who has significant interaction with adult males will enter puberty earlier than juvenile females who are not socially overexposed to adult males. The average age at which puberty begins may be affected by ethnicity as well. For example, the average age of menarche in various populations surveyed has ranged from 12 to 18 years. The earliest average onset of puberty

2496-478: Is the issue of body image . As they physically develop, gaining weight in several areas of the body, early-maturing females usually look larger than females who have not yet entered puberty. A result of the social pressure to be thin, the early-maturing females develop a negative view of their body image. In addition, people may tease the females about their visible breasts, forcing the early-maturing female to hide her breasts by dressing differently. Embarrassment about

2592-519: Is the process of physical changes through which a child 's body matures into an adult body capable of sexual reproduction . It is initiated by hormonal signals from the brain to the gonads : the ovaries in a female, the testicles in a male. In response to the signals, the gonads produce hormones that stimulate libido and the growth, function, and transformation of the brain, bones , muscle , blood , skin , hair , breasts , and sex organs . Physical growth —height and weight—accelerates in

2688-419: Is usually a firm, tender lump under the center of the areola of one or both breasts , occurring on average at about 10½ years of age. This is referred to as thelarche . By the widely used Tanner staging of puberty, this is stage 2 of breast development (stage 1 is a flat, prepubertal breast). Within 6–12 months, the swelling has clearly begun in both sides, softened, and can be felt and seen extending beyond

2784-511: Is worn in the resulting opening. Mammal A mammal (from Latin mamma  'breast') is a vertebrate animal of the class Mammalia ( / m ə ˈ m eɪ l i . ə / ). Mammals are characterized by the presence of milk -producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair , and three middle ear bones . These characteristics distinguish them from reptiles and birds , from which their ancestors diverged in

2880-490: The American Academy of Pediatrics states there is "little evidence to affirm the association between circumcision status and optimal penile hygiene", various studies suggest that males be educated about the role of hygiene, including retracting the foreskin while urinating and rinsing under it and around the glans at each bathing opportunity. Regular washing under the foreskin was found by Krueger and Osborn (1986) to reduce

2976-517: The Carboniferous Period over 300 million years ago. Around 6,400 extant species of mammals have been described and divided into 27 orders . The largest orders of mammals, by number of species , are the rodents , bats , and Eulipotyphla (including hedgehogs , moles and shrews ). The next three are the primates (including humans , monkeys and lemurs ), the even-toed ungulates (including pigs , camels , and whales ), and

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3072-519: The Carnivora (including cats , dogs , and seals ). Mammals are the only living members of Synapsida ; this clade , together with Sauropsida (reptiles and birds), constitutes the larger Amniota clade. Early synapsids are referred to as " pelycosaurs ." The more advanced therapsids became dominant during the Guadalupian . Mammals originated from cynodonts , an advanced group of therapsids, during

3168-467: The Cretaceous . The relationships between these three lineages is contentious, and all three possible hypotheses have been proposed with respect to which group is basal . These hypotheses are Atlantogenata (basal Boreoeutheria), Epitheria (basal Xenarthra) and Exafroplacentalia (basal Afrotheria). Boreoeutheria in turn contains two major lineages— Euarchontoglires and Laurasiatheria . Estimates for

3264-550: The International Union for Conservation of Nature (IUCN) completed a five-year Global Mammal Assessment for its IUCN Red List , which counted 5,488 species. According to research published in the Journal of Mammalogy in 2018, the number of recognized mammal species is 6,495, including 96 recently extinct. The word " mammal " is modern, from the scientific name Mammalia coined by Carl Linnaeus in 1758, derived from

3360-547: The Latin mamma ("teat, pap"). In an influential 1988 paper, Timothy Rowe defined Mammalia phylogenetically as the crown group of mammals, the clade consisting of the most recent common ancestor of living monotremes ( echidnas and platypuses ) and therian mammals ( marsupials and placentals ) and all descendants of that ancestor. Since this ancestor lived in the Jurassic period, Rowe's definition excludes all animals from

3456-481: The androgen testosterone is the principal sex hormone ; while testosterone is produced, all males' changes are characterized as virilization . A substantial product of testosterone metabolism in males is the estrogen estradiol . The conversion of testosterone to estradiol depends on the amount of body fat and estradiol levels in males are typically much lower than in females. The male "growth spurt" also begins later, accelerates more slowly, and lasts longer before

3552-612: The beard area. As with most human biological processes, this specific order may vary among some individuals. Arm, leg, chest , abdominal , and back hair become heavier more gradually. There is a large range in amount of body hair among adult men, and significant differences in timing and quantity of hair growth among different racial groups. Facial hair is often present in late adolescence, but may not appear until significantly later. Facial hair will continue to get coarser, darker and thicker for another 2–4 years after puberty. Some men do not develop full facial hair for up to 10 years after

3648-539: The biological classification scheme used, are the primates : apes , monkeys , and lemurs ; the Cetartiodactyla : whales and even-toed ungulates ; and the Carnivora which includes cats , dogs , weasels , bears , seals , and allies. According to Mammal Species of the World , 5,416 species were identified in 2006. These were grouped into 1,229  genera , 153  families and 29 orders. In 2008,

3744-405: The clitoral glans , and the clitoral hood . The labia minora meet posteriorly at the frenulum of the labia minora (also known as the fourchette), which is a fold of skin below the vaginal orifice. The fourchette is more prominent in younger women, and often recedes after sexual activity and childbirth. When standing or with the legs together, the labia majora usually entirely or partially cover

3840-456: The epiphyses fuse. Although males are on average 2 centimetres (0.8 in) shorter than females before puberty begins, adult men are on average about 13 centimetres (5.1 in) taller than women. Most of this sex difference in adult heights is attributable to a later onset of the growth spurt and a slower progression to completion, a direct result of the later rise and lower adult male levels of estradiol. The hormonal maturation of females

3936-561: The follicles in the ovaries increase in size. The ovaries usually contain small follicular cysts visible by ultrasound . The first menstrual bleeding is referred to as menarche , and typically occurs about two years after thelarche . The average age of menarche is 12½ in the United States . Most American females experience their first period at 11, 12 or 13, but some experience it earlier than their 11th birthday and others after their 14th birthday. In fact, anytime between 8 and 16

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4032-408: The labioscrotal swellings become the labia majora. The genital tissues are greatly influenced by natural fluctuations in hormone levels, which lead to changes in labia size, appearance, and elasticity at various life stages. At birth, the labia minora are well-developed, and the labia majora appear plump due to being exposed to maternal hormones in the womb. The labia majora have the same color as

4128-411: The morphologic changes in size, shape, composition, and functioning of the pubertal body, is the development of secondary sex characteristics, the "filling in" of the child's body; from girl to woman, from boy to man. Derived from the Latin puberatum (age of maturity), the word puberty describes the physical changes to sexual maturation, not the psychosocial and cultural maturation denoted by

4224-404: The pelvis and thus hips widen (providing a larger birth canal ). Fat tissue increases to a greater percentage of the body composition than in males, especially in the typical female distribution of breasts, hips, buttocks, thighs, upper arms, and pubis. Progressive differences in fat distribution as well as sex differences in local skeletal growth contribute to the typical female body shape by

4320-487: The "pubic triangle". Stage 5 refers to spread of pubic hair to the thighs and sometimes as abdominal hair upward towards the navel . In about 15% of females, the earliest pubic hair appears before breast development begins. Perineal skin keratinizes due to effect of estrogen increasing its resistance to infection. The mucosal surface of the vagina also changes in response to increasing levels of estrogen , becoming thicker and duller pink in color (in contrast to

4416-579: The Late Triassic to Early Jurassic . Mammals achieved their modern diversity in the Paleogene and Neogene periods of the Cenozoic era, after the extinction of non-avian dinosaurs , and have been the dominant terrestrial animal group from 66 million years ago to the present. The basic mammalian body type is quadrupedal , with most mammals using four limbs for terrestrial locomotion ; but in some,

4512-505: The action of estrogen—an important reproduction and development regulator. It leaches out of plastic into liquids and foods, and the Centers for Disease Control and Prevention (CDC) found measurable amounts of BPA in the bodies of more than 90 percent of the U.S. population studied. The highest estimated daily intakes of BPA occur in infants and children. Many plastic baby bottles contain BPA, and BPA

4608-425: The breasts and uterus , it is also the principal hormone driving the pubertal growth spurt and epiphyseal maturation and closure. Puberty is preceded by adrenarche , marking an increase of adrenal androgen production between ages 6–10. Adrenarche is sometimes accompanied by the early appearance of axillary and pubic hair. The first androgenic hair resulting from adrenarche can be also transient and disappear before

4704-421: The brighter red of the prepubertal vaginal mucosa). Mucosa changes into a multilayered structure with superficial layer of squamous cells. Estrogen increase glycogen content in vaginal epithelium , which in future plays important part in maintaining vaginal pH . Whitish secretions (physiologic leukorrhea ) are a normal effect of estrogen as well. In the two years following thelarche, the uterus , ovaries , and

4800-492: The candidates is an androgen receptor gene. Researchers have hypothesized that early puberty onset may be caused by certain hair care products containing estrogen or placenta, and by certain chemicals, namely phthalates , which are used in many cosmetics, toys, and plastic food containers. There is theoretical concern, and animal evidence, that environmental hormones and chemicals may affect aspects of prenatal or postnatal sexual development in humans. Bisphenol A (BPA)

4896-807: The clade originating with the last common ancestor of Sinoconodon and living mammals. The earliest-known synapsid satisfying Kemp's definitions is Tikitherium , dated 225 Ma , so the appearance of mammals in this broader sense can be given this Late Triassic date. However, this animal may have actually evolved during the Neogene. As of the early 21st century, molecular studies based on DNA analysis have suggested new relationships among mammal families. Most of these findings have been independently validated by retrotransposon presence/absence data . Classification systems based on molecular studies reveal three major groups or lineages of placental mammals— Afrotheria , Xenarthra and Boreoeutheria —which diverged in

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4992-433: The clitoris and other parts of the vulva, which causes pleasurable orgasmic sensations. Following orgasm or when no longer sexually aroused, the labia gradually return to their unaroused state. The labia minora return to their original color within 2 minutes, and engorgement dissipates in about 5 to 10 minutes. The labia majora return to their pre-arousal state in approximately 1 hour. In many cultures and locations all over

5088-444: The closest thing to an official classification of mammals, despite its known issues. Most mammals, including the six most species-rich orders , belong to the placental group. The three largest orders in numbers of species are Rodentia : mice , rats , porcupines , beavers , capybaras , and other gnawing mammals; Chiroptera : bats; and Eulipotyphla : shrews , moles , and solenodons . The next three biggest orders, depending on

5184-468: The completion of puberty. Under the influence of androgens, the larynx (or voice box) grows in both sexes. This growth is far more prominent in males, causing the male voice to drop and deepen, sometimes abruptly but rarely "overnight", about one octave , because the longer and thicker vocal folds have a lower fundamental frequency . Before puberty, the larynx of males and females is about equally small. The first physical sign of puberty in females

5280-468: The diminished effects of maternal hormones. The labia minora become less prominent. During puberty , increased hormone levels often significantly change the appearance of the labia. The labia minora become more elastic, prominent, and wrinkled. The labia majora regain fat, and begin growing pubic hair close to the pudendal cleft. Hair is initially sparse and straight, but gradually becomes darker, denser, and curlier as growth spreads outward and upward toward

5376-1311: The divergence times between these three placental groups range from 105 to 120 million years ago, depending on the type of DNA used (such as nuclear or mitochondrial ) and varying interpretations of paleogeographic data. Monotremata Marsupialia Xenarthra Afrotheria Glires Euarchonta [REDACTED] Eulipotyphla Chiroptera Pholidota Carnivora [REDACTED] Perissodactyla [REDACTED] Artiodactyla [REDACTED] Monotremata [REDACTED] Paucituberculata [REDACTED] Didelphimorphia [REDACTED] Microbiotheria Notoryctemorphia [REDACTED] Peramelemorphia [REDACTED] Dasyuromorphia [REDACTED] Diprotodontia [REDACTED] Cingulata [REDACTED] Pilosa [REDACTED] Hyracoidea [REDACTED] Sirenia [REDACTED] Proboscidea [REDACTED] Tubulidentata [REDACTED] Macroscelidea [REDACTED] Afrosoricida [REDACTED] Eulipotyphla [REDACTED] Chiroptera [REDACTED] Pholidota [REDACTED] Carnivora [REDACTED] Perissodactyla [REDACTED] Artiodactyla [REDACTED] Scandentia [REDACTED] Lagomorpha [REDACTED] Puberty Puberty

5472-574: The earlier Triassic , despite the fact that Triassic fossils in the Haramiyida have been referred to the Mammalia since the mid-19th century. If Mammalia is considered as the crown group, its origin can be roughly dated as the first known appearance of animals more closely related to some extant mammals than to others. Ambondro is more closely related to monotremes than to therian mammals while Amphilestes and Amphitherium are more closely related to

5568-441: The edges of the areolae. This is stage 3 of breast development. By another 12 months (stage 4), the breasts are approaching mature size and shape, with areolae and nipples forming a secondary mound. In most young women, this mound disappears into the contour of the mature breast (stage 5), although there is so much variation in sizes and shapes of adult breasts that stages 4 and 5 are not always separately identifiable. Pubic hair

5664-581: The effects of an early or a late onset of puberty in males and females. In general, females who enter puberty late experience positive outcomes in adolescence and adulthood, while females who enter puberty early experience negative outcomes. Males who have earlier pubertal timing generally have more positive outcomes in adulthood but more negative outcomes in adolescence, while the reverse is true for later pubertal timing. Outcomes have generally indicated that early onset of puberty in females can be psychologically damaging. The main reason for this detrimental effect

5760-414: The end of puberty. On average, at 10 years, females have 6% more body fat than males. Rising levels of androgens can change the fatty acid composition of perspiration , resulting in a more "adult" body odor . This often precedes thelarche and pubarche by one or more years. Another androgen effect is increased secretion of oil ( sebum ) from the skin. This change increases the susceptibility to acne ,

5856-451: The end of the 20th century. However, since 1945, a large amount of new and more detailed information has gradually been found: The paleontological record has been recalibrated, and the intervening years have seen much debate and progress concerning the theoretical underpinnings of systematization itself, partly through the new concept of cladistics . Though fieldwork and lab work progressively outdated Simpson's classification, it remains

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5952-437: The enlargement of the testicles and scrotum . The penis also increases in size, and a male develops pubic hair. A male's testicles also begin making sperm . The release of semen , which contains sperm and other fluids, is called ejaculation . During puberty, a male's erect penis becomes capable of ejaculating semen and impregnating a female. A male's first ejaculation is an important milestone in his development. On average,

6048-415: The females' womanly physique and femaleish innocence." While having an older malefriend might improve popularity among peers, it also increases the risk of alcohol and drug use, increased sexual relations (often unprotected), eating disorders and bullying. Generally, later onset of puberty in females produces positive outcomes. They exhibit positive behaviors in adolescence that continue to adulthood. In

6144-554: The first half of puberty and is completed when an adult body has been developed. Before puberty, the external sex organs, known as primary sexual characteristics , are sex characteristics that distinguish males and females. Puberty leads to sexual dimorphism through the development of the secondary sex characteristics , which further distinguish the sexes. On average, females begin puberty at age 10½ and complete puberty at ages 15-17; males begin at ages 11½-12 and complete puberty at ages 16-17. The major landmark of puberty for females

6240-443: The functioning of the lower urinary tract. Hair growth develops under the arms, starting out sparse before thickening and darkening over time. In a general sense, the conclusion of puberty is reproductive maturity. Criteria for defining the conclusion may differ for different purposes: attainment of the ability to reproduce, achievement of maximal adult height, maximal gonadal size, or adult sex hormone levels. Maximal adult height

6336-447: The glans. The foreskin then gradually becomes retractable. Research by Øster (1968) found that with the onset and continuation of puberty, the proportion of males able to pull back their foreskins increased. At ages 12–13, Øster found that only 60% of males were able to retract their foreskins; this increased to 85% by ages 14–15, and 95% by 16–17. He also found that 1% of those unable to fully retract experienced phimosis at ages 14–17,

6432-411: The inner and outer labia are removed and the vulva is sewn shut. FGM is mostly outlawed around the world, even in countries where the practice is widespread. Labiaplasty is a controversial plastic surgery procedure that involves the creation or reshaping of the labia. Labia piercing is a cosmetic piercing, usually with a special needle under sterile conditions, of the inner or outer labia. Jewelry

6528-505: The inner and outer surfaces of the labia majora contain sebaceous glands (oil glands), apocrine sweat glands , and eccrine sweat glands . The labia majora have fewer superficial nerve endings than the rest of the vulva, but the skin is highly vascularized. The internal surface of the labia minora is a thin moist skin, with the appearance of a mucous membrane. They contain many sebaceous glands, and occasionally have eccrine sweat glands. The labia minora have many sensory nerve endings, and have

6624-401: The labia majora swell due to increased blood flow to the region, and slightly draw back, revealing the inner labia. The labia minora become engorged with blood, causing them to expand in diameter by two to three times, and darken or redden in color. Because pregnancy and childbirth increase genital vascularity, the inner and outer labia will engorge faster in women who have had children. After

6720-456: The labia minora are sexually responsive, and sensitivity varies greatly. In some, they are so sensitive that anything other than light touch may be uncomfortable, whereas stimulation may elicit no sexual response in others. The labia may be sexually stimulated as part of masturbation or with a sex partner , such as by fingering or oral sex . Moving the labia minora can also stimulate the extremely sensitive clitoris. During sexual arousal ,

6816-411: The labia minora to darken in color. Later in life, the labia majora once again gradually lose fat, becoming flatter and more wrinkled, and pubic hair turns grey. Following menopause, falling hormone levels cause further changes to the labia. The labia minora atrophy, making them become less elastic, and pubic hair on the labia majora becomes more sparse. The labia are an erogenous zone . In particular,

6912-451: The limbs are adapted for life at sea , in the air , in trees or underground . The bipeds have adapted to move using only the two lower limbs, while the rear limbs of cetaceans and the sea cows are mere internal vestiges . Mammals range in size from the 30–40 millimetres (1.2–1.6 in) bumblebee bat to the 30 metres (98 ft) blue whale —possibly the largest animal to have ever lived. Maximum lifespan varies from two years for

7008-417: The moist, sensitive inner surfaces of the vulva, which indirectly protects the vagina and urethra, much like the lips protect the mouth. The outer surface of the labia majora is pigmented skin, and develops pubic hair during puberty. The inner surface of the labia majora is smooth, hairless skin, which resembles a mucous membrane, and is only visible when the labia majora and labia minora are drawn apart. Both

7104-517: The normal population. After the male's testicles have enlarged and developed for about one year, the length and then the breadth of the shaft of the penis will increase and the glans penis and corpora cavernosa will also start to enlarge to adult proportions. Erections during sleep or when waking up are medically known as nocturnal penile tumescence and colloquially referred to as morning wood . The penis can regularly get erect during sleep and men or males often wake up with an erection. Once

7200-466: The onset of puberty is physical changes to a person's body. These physical changes are the first visible signs of neural, hormonal, and gonadal function changes. The age at which puberty begins varies between individuals; usually, puberty begins between 10 and 13 years of age. The age at which puberty begins is affected by both genetic factors and by environmental factors such as nutritional state and social circumstances. An example of social circumstances

7296-584: The onset of puberty, and then decline to adult levels when puberty is completed. The rise in GnRH might also be caused by genetics. A study discovered that a mutation in genes encoding both neurokinin B as well as the neurokinin B receptor can alter the timing of puberty. The researchers hypothesized that neurokinin B might play a role in regulating the secretion of kisspeptin , a compound responsible for triggering direct release of GnRH as well as indirect release of LH and FSH. Several studies about puberty have examined

7392-534: The onset of true puberty. The onset of puberty is associated with high GnRH pulsing, which precedes the rise in sex hormones, LH and FSH . Exogenous GnRH pulses cause the onset of puberty. Brain tumors which increase GnRH output may also lead to premature puberty . The cause of the GnRH rise is unknown. Leptin might be the cause of the GnRH rise. Leptin has receptors in the hypothalamus which synthesizes GnRH. Individuals who are deficient in leptin fail to initiate puberty. The levels of leptin increase with

7488-435: The past, early onset of puberty in males has been associated with positive outcomes, such as leadership in high school and success in adulthood. However, recent studies have revealed that the risks and problems of early maturation in males might outweigh the benefits. Early-maturing males develop "more aggressive, law-breaking, and alcohol abusing" behaviors, which result in anger towards parents and trouble in school and with

7584-448: The phenomenon could be linked to obesity or exposure to chemicals in the food chain, and is putting females at greater long-term risk of breast cancer. Various studies have found direct genetic effects to account for at least 46% of the variation of timing of puberty in well-nourished populations. The genetic association of timing is strongest between mothers and daughters. The specific genes affecting timing are not yet known. Among

7680-505: The police. Early puberty also correlates with increased sexual activity and a higher instance of teenage pregnancy, both of which can lead to depression and other psychosocial issues. On the other hand, late-maturing males develop lower self-esteem and confidence and generally have lower popularity among peers, due to their less-developed physiques. Also, they experience problems with anxiety and depression and are more likely to be afraid of sex than other males. In males, puberty begins with

7776-415: The production of ultrasound , scent marking , alarm signals , singing , echolocation ; and, in the case of humans, complex language . Mammals can organize themselves into fission–fusion societies , harems , and hierarchies —but can also be solitary and territorial . Most mammals are polygynous , but some can be monogamous or polyandrous . Domestication of many types of mammals by humans played

7872-431: The rate of puberty as it occurs now is the intended way. Growth spurts began at around 10-12, but markers of later stages of puberty such as menarche had delays that correlated with severe environmental conditions such as poverty, poor nutrition, air and pollution. Puberty that starts earlier than usual is known as precocious puberty , and puberty which starts later than usual is known as delayed puberty . Notable among

7968-499: The remainder were partially able to. The findings were supported by further research by Kayaba et al (1996) on a sample of over 600 males, and Ishikawa and Kawakita (2004) found that by age 15, 77% of their sample of males could retract their foreskins. Beaugé (1997) reports that males may assist the development of retractile foreskin by manual stretching. Once a male is able to retract his foreskin, penile hygiene should become an important feature of his routine body care. Although

8064-491: The risk of numerous penile disorders, however Birley et al. (1993) reports excessive washing with soap should be avoided because it dries the oils out of the tissues and can cause non-specific dermatitis . In the months and years following the appearance of pubic hair, other areas of skin that respond to androgens may develop androgenic hair . The usual sequence is: underarm (axillary) hair , perianal hair , upper lip hair , sideburn (preauricular) hair, periareolar hair, and

8160-503: The shrew to 211 years for the bowhead whale . All modern mammals give birth to live young, except the five species of monotremes , which lay eggs. The most species-rich group is the viviparous placental mammals , so named for the temporary organ ( placenta ) used by offspring to draw nutrition from the mother during gestation . Most mammals are intelligent , with some possessing large brains, self-awareness , and tool use . Mammals can communicate and vocalize in several ways, including

8256-476: The subsequent result of a failure to commence or complete puberty, secondary hypogonadism and infertility . The average age at which the onset of puberty occurs has dropped significantly since the 1840s. A 2006 study in Denmark found that puberty, as evidenced by breast development, started at an average age of 9 years and 10 months, a year earlier than when a similar study was done in 1991. Scientists believe

8352-455: The surrounding skin. Labial adhesions can occur between the ages of 3 months and 2 years, and may make the vulva look flat. These adhesions are not usually a cause for concern, and usually disappear without treatment. Treatment options may include estrogen cream, manual separation with local anesthesia, or surgical separation under sedation. During early childhood, the labia majora look flat and smooth because of decreasing levels of body fat, and

8448-461: The term adolescent development in Western culture , wherein adolescence is the period of mental transition from childhood to adulthood , which overlaps much of the body's period of puberty. Two of the most significant differences between puberty in females and puberty in males are the age at which it begins, and the major sex steroids involved, the androgens and the estrogens . Although there

8544-448: The testicles is among the parameters of the Tanner scale for male genitals , from stage I which represents a volume of less than 1.5 ml, to stage V which represents a testicular volume of greater than or equal to 20 ml. Testicular size reaches maximal adult size about 6 years after the onset of puberty. While 18–20 cm is an average adult size, there is wide variation in testicular size in

8640-537: The therians; as fossils of all three genera are dated about 167 million years ago in the Middle Jurassic , this is a reasonable estimate for the appearance of the crown group. T. S. Kemp has provided a more traditional definition: " Synapsids that possess a dentary – squamosal jaw articulation and occlusion between upper and lower molars with a transverse component to the movement" or, equivalently in Kemp's view,

8736-419: The thighs and mons pubis. At the end of puberty, pubic hair will be coarse, curly, and fairly thick. The patch of pubic hair covering the genitals will eventually often form a triangle shape. By adulthood, the outer surface of the labia majora may be darker than the surrounding skin, and may have wrinkles. During the reproductive years, if a woman delivers a child, the fourchette will flatten. Pregnancy may cause

8832-404: The third year and 10% in the sixth year. Initiation of ovulation after menarche is not inevitable. A high proportion of females with continued irregularity in the menstrual cycle several years from menarche will continue to have prolonged irregularity and anovulation, and are at higher risk for reduced fertility. During this period, also in response to rising levels of estrogen, the lower half of

8928-413: The vulva to form the pudendal cleft through the middle. They enclose and protect the other tissues of the vulva. The labia majora often have a plump appearance, and are thicker towards the anterior. The anterior junction of the labia majora is called the anterior commissure , which is below the mons pubis and above the clitoris. To the posterior, the labia majora join at the posterior commissure , which

9024-483: The vulva. This can lead viewers of pornography to have unrealistic expectations about how the labia should look. Similar to how some women develop self-esteem issues from comparing their faces and bodies to airbrushed models in magazines, women who compare their vulvas to idealized pornographic images may believe their own labia are abnormal. This can have a negative impact on a woman's life, since genital self-consciousness makes it more difficult to enjoy sexual activity, see

9120-540: The width of the spread may reflect unevenness of wealth and food distribution in a population. Researchers have identified an earlier age of the onset of puberty. However, they have based their conclusions on a comparison of data from 1999 with data from 1969. In the earlier example, the sample population was based on a small sample of white females (200, from Britain). The later study identified as puberty as occurring in 48% of African-American females by age nine, and 12% of white females by that age. One possible cause of

9216-651: The world, the labia, as part of the genitalia , are considered private, or intimate parts , whose exposure (especially in public ) is governed by fairly strict socio-cultural mores . In many cases, public exposure is limited, and often prohibited by law. Views on pubic hair differ between people and between cultures. Some women prefer the look or feel of pubic hair, while others may choose to remove some or all of it. Temporary methods of removal include shaving , trimming, waxing , sugaring and depilatory products while permanent hair removal can be accomplished using electrolysis or laser hair removal . In Korea, pubic hair

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