Adolescence (lat adolescere = (to) grow) is a transitional stage of physical and mental human development that occurs between childhood and adulthood. This transition involves biological (i.e. pubertal), social, and psychological changes, though the biological or physiological ones are the easiest to measure objectively. Historically, puberty has been heavily associated with teenagers and the onset of adolescent development.[1][2][3][4] In recent years, however, the start of puberty has seen an increase in preadolescence and extension beyond the teenage years, making adolescence less simple to discern.[1][5][2] The end of adolescence and the beginning of adulthood varies by country as well as by function, as even within a single country there will be different ages at which an individual is considered mature enough to be entrusted with particular tasks, such as driving a vehicle, having sexual relations, serving in the armed forces, voting, or marrying. In common usage around the world, "adolescent", "teenager", "teen", "youth", "young adult", "lighty", "youngster", "youngin", "young person" and "emerging adult" may be considered synonyms - although the term 'teenager' is an artifact of the English counting system, something which does not occur in all languages.[6] In sociology, adolescence is seen as a cultural phenomenon for the working world and therefore its end points are not easily tied to physical milestones. The World Health Organization defines adolescence as the period of life between 10 and 19 years of age.[7] A person between early childhood and the teenage years is sometimes referred to as a pre-teen or tween. The ages of adolescence vary by culture. Teenagers (ages 13-19) are usually defined as signifying adolescence. Puberty is the stage of the lifespan in which a child develops secondary sex characteristics (for example a deeper voice or larger adam's apple in boys, and development of breasts and more curved and prominent hips in girls) as his or her hormonal balance shifts strongly towards an adult state. This is triggered by the pituitary gland, which secretes a surge of hormones, such as testosterone (boys) or estrogen (girls) into the blood stream and begins the rapid maturation of the gonads: the girl's ovaries and the boy's testicles. Some boys may develop Gynecomastia due to an imbalance of sex hormones, tissue responsiveness or obesity. Put simply, puberty is the time when a child's body starts changing to look more like an adult. The onset of puberty in girls appears to be related to body fat percentage. In most Western countries, the average age of a girl's first menstrual period, or menarche, fell in a decreasing secular trend.[citation needed] Girls start going through puberty earlier than boys. The average age for girls to start puberty is 10-12 while the average age for boys to start puberty is 12-14. Adolescent psychology is associated with notable changes in mood sometimes known as Mood swings. Cognitive, emotional and attitudinal changes which are characteristic of adolescence, often take place during this period, and this can be a cause of conflict on one hand and positive personality development on the other. Because the adolescents are experiencing various strong cognitive and physical changes, for the first time in their lives they may start to view their friends, their peer group, as more important and influential than their parents/guardians. Because of peer pressure, they may sometimes indulge in activities not deemed socially acceptable, although this may be more of a social phenomenon than a psychological one.[9] The home is an important aspect of adolescent psychology: home environment and family have a substantial impact on the developing minds of teenagers, and these developments may reach a climax during adolescence. For example, abusive parents may lead a child to "poke fun" at other classmates when he/she is seven years old or so, but during adolescence, it may become progressively worse, for example, the child may now be using drugs or becoming intolerably violent among other classmates. If the concepts and theory behind of right or wrong were not established early on in a child's life, the lack of this knowledge may impair a teenager's ability to make beneficial decisions as well as allowing his impulses to control his decisions. In the search for a unique social identity for themselves, adolescents are frequently confused about what is 'right' and what is 'wrong.' G. Stanley Hall denoted this period as one of "Storm and Stress" and, according to him, conflict at this developmental stage is normal and not unusual. Margaret Mead, on the other hand, attributed the behavior of adolescents to their culture and upbringing.[10] However, Piaget, attributed this stage in development with greatly increased cognitive abilities; at this stage of life the individual's thoughts start taking more of an abstract form and the egocentric thoughts decrease, hence the individual is able to think and reason in a wider perspective.[11] Positive psychology is sometimes brought up when addressing adolescent psychology as well. This approach towards adolescents refers to providing them with motivation to become socially acceptable and notable individuals, since many adolescents find themselves bored, indecisive and/or unmotivated.[12] Adolescents may be subject to peer pressure within their adolescent time span, consisting of the need to have sex, consume alcoholic beverages, use drugs, defy their parental figures, or commit any activity in which the person who is subjected to may not deem appropriate, among other things. Peer pressure is a common experience between adolescents and may result briefly or on a larger scale. It should also be noted that adolescence is the stage of a psychological breakthrough in a person's life when the cognitive development is rapid[13] and the thoughts, ideas and concepts developed at this period of life greatly influence the individual's future life, playing a major role in character and personality formation.[14] Struggles with adolescent identity and depression usually set in when an adolescent experiences a loss. The most important loss in their lives is the changing relationship between the adolescent and their parents. Teen depression can be extremely intense at times because of physical and hormonal changes but emotional instability is part of being a teenager. Their changing mind, body and relationships often present themselves as stressful and that change, they assume, is something to be feared.[15] Views of family relationships during adolescence are changing. The old view of family relationships during adolescence put an emphasis on conflict and disengagement and thought storm and stress was normal and even inevitable. However, the new view puts emphasis on transformation or relationships and maintenance of connectedness. Adolescent sexuality refers to sexual feelings, behavior and development in adolescents and is a stage of human sexuality. Sexuality and sexual desire usually begins to appear along with the onset of puberty. The expression of sexual desire among adolescents (or anyone, for that matter), might be influenced by family values and influences, the culture and religion they have grown up in social engineering, social control, taboos, and other kinds of social mores. The risks of adolescent sexual activity is sometimes associated with: emotional distress (fear of abuse or exploitation), sexually transmitted diseases (including HIV/AIDS) and pregnancy through failure or non-use of contraceptives. In terms of sexual identity, sexual orientation among adolescents may vary greatly across the spectrum from heterosexuality and LGBT orientations to pansexuality and sexual fetishism. According to anthropologist Margaret Mead and psychologist Albert Bandura, the turmoil found in adolescence in Western society has a cultural rather than a physical cause; they reported that societies where young women engaged in free sexual activity had no such adolescent turmoil, (that is until more recently, when information about the most dangerous STDs was made publicly accessible.) The age of consent to sexual activity varies widely between international jurisdictions, ranging from 12 to 21 years, although some governments, such as Canada's, are planning to raise the age to at least 16 in an effort to reduce the incidence of the most serious STD's, pregnancy among teenage girls, and the sexual abuse and exploitation of younger teens. In commerce, this generation is seen as an important target. Mobile phones, contemporary popular music, movies, television programs, sports, video games and clothes are heavily marketed and often popular amongst adolescents. In the past (and still in some cultures) there were ceremonies that celebrated adulthood, typically occurring during adolescence. Seijin shiki (literally "adult ceremony") is a Japanese example of this. Upanayanam is a coming of age ceremony for males in the Hindu world. In Judaism, 12 year old girls and 13-year-old boys become Bat or Bar Mitzvah, respectively, and often have a celebration to mark this coming of age. Among some denominations of Christianity, the rite or sacrament of Confirmation is received by adolescents and may be considered the time at which adolescents become members of the church in their own right. African boys also have a coming of age ceremony in which, upon reaching adolescence, the males state a promise to never do anything to shame their families or their village. This was also continued among African-American slaves in the early days of slavery before the practice was outlawed. In United States, girls will often have a "sweet sixteen" party to celebrate turning the aforementioned age, a tradition similar to the quinceañera in Latin culture. In modern America, events such as getting your first driver's license, high school and later on college graduation and first career related job are thought of as being more significant markers in transition to adulthood. Adolescents have also been an important factor in many movements for positive social change around the world. The popular history of adolescents participating in these movements may perhaps start with Joan of Arc, and extend to present times with popular youth activism, student activism, and other efforts to make the youth voice heard. Internationally, those over a certain age (often 18, though this varies) are legally considered to have reached the age of majority and are regarded as adults and are held to be responsible for their actions. People below this age are considered minors and are children. A person below the age of majority may gain adult rights through legal emancipation. Teenagers may be rebellious because they want to have the same rights and freedoms as adults. As a result some of those teens may obtain counterfeit ID/licenses which allow them to partake of those privileges. On the other hand, many teens are in no particular hurry to abandon their younger years, and enjoy their childhood. Those who are under the age of consent, or legal responsibility, may be considered too young to be held accountable for criminal action. This is called the defense of infancy. The age of criminal responsibility varies from 7 in India to 18 in Belgium. After reaching the initial age, there may be levels of responsibility dictated by age and type of offense, and crimes committed by minors may be tried in a juvenile court. The legal working age in Western countries is usually 14 to 16, depending on the number of hours and type of employment. In the United Kingdom and Canada, for example, young people between 14 and 16 can work at certain types of light work with some restrictions to allow for schooling; while kids over 16 can work full-time (excluding night work). Many countries also specify a minimum school leaving age, ranging from 10 to 18, at which a person is legally allowed to leave compulsory education. The age of consent to sexual activity varies widely between jurisdictions, ranging from 12 to 21 years, although 14 to 16 years is more usual. Sexual intercourse with a person below this age is treated as the crime of statutory rape. Some jurisdictions allow an exemption where both partners are close in age - for example, two 15 year olds. The age at which people are allowed to marry also varies, from 9 in Yemen to 22 for males and 20 for females in China. In Western countries, people are typically allowed to marry at 18, although they are sometimes allowed to marry at a younger age with parental or court consent. In developing countries, the legal marriageable age does not always correspond with the age at which people actually marry; for example, the legal age for marriage in Ethiopia is 18 for both males and females, but in rural areas most girls are married by age 16. In most democratic countries, a citizen is eligible to vote at 18. For example, in the United States, the Twenty-sixth amendment decreased the voting age from 21 to 18. In a minority of countries, the voting age is 17 (for example, Indonesia) or 16 (for example, Brazil). By contrast, some countries have a minimum voting age of 21 (for example, Singapore) whereas the minimum age in Uzbekistan is 25. Age of candidacy is the minimum age at which a person can legally qualify to hold certain elected government offices. In most countries, a person must be 18 or over to stand for elected office, but some countries such as the United States and Italy have further restrictions depending on the type of office. The sale of selected items such as cigarettes, alcohol, and videos with violent or pornographic content is also restricted by age in most countries. In the U.S, the minimum age to buy an R-rated movie, M-rated game or an album with a parental advisory label is 17 (in some states 18). In practice, it is common that young people engage in underage smoking or drinking, and in some cultures this is tolerated to a certain degree. In the United States, teenagers are allowed to drive between 14-18 (each state sets its own minimum driving age of which a curfew may be imposed), in the US, adolescents 17 years of age can serve in the military. The age at which teens are allowed to serve in the military is generally younger than the legal drinking age. In Europe it is more common for the driving age to be higher (usually 18) while the drinking age is lower than that of the US (usually 16 or 18). In Canada, the drinking age is 18 in some areas and 19 in other areas. In Australia, universally the minimum drinking age is 18, unless a person is in a private residence or is under parental supervision in a licensed premises. The driving age varies from state to state but the more common system is a graduated system of "L plates" (a learning license that requires supervision from a licensed driver) from age 16, red "P plates" (probationary license) at 17, green "P plates" at 18 and finally a full license, i.e. for most people around the age of 20. The legal gambling age also depends on the jurisdiction, although it is typically 18. The minimum age for donating blood in the U.S is 17 although it may be 16 with parental permission in some states such as New York.[citation needed] A number of social scientists, including anthropologist Margaret Mead and sociologist Mike Males, have noted the contradictory treatment of laws affecting adolescents in the United States. As Males has noted, the US Supreme Court has, "explicitly ruled that policy-makers may impose adult responsibilities and punishments on individual youths as if they were adults at the same time laws and policies abrogate adolescents’ rights en masse as if they were children." The issue of youth activism affecting political, social, educational, and moral circumstances is of growing significance around the world. Youth-led organizations around the world have fought for social justice, the youth vote seeking to gain teenagers the right to vote, to secure more youth rights, and demanding better schools through student activism. Since the advent of the Convention on the Rights of the Child in 1989 (children defined as under 18), almost every country (except the U.S. & Somalia) in the world has become voluntarily legally committed to advancing an anti-discriminatory stance towards young people of all ages. This is a legally binding document which secures youth participation throughout society while acting against unchecked child labor, child soldiers, child prostitution, and pornography.