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Biologically, an adult is a human being or other organism that has reached sexual maturity. In human context, the term ''adult'' additionally has meanings associated with social and legal concepts. In contrast to a "minor", a legal adult is a person who has attained the age of majority and is therefore regarded as independent, self-sufficient, and responsible. Human adulthood encompasses psychological adult development. Definitions of adulthood are often inconsistent and contradictory; a person may be biologically an adult, and have adult behavior but still be treated as a child if they are under the legal age of majority. Conversely, one may legally be an adult but possess none of the maturity and responsibility that may define an adult character. In different cultures there are events that relate passing from being a child to becoming an adult or coming of age. This often encompasses the passing a series of tests to demonstrate that a person is prepared for adulthood, or reaching a specified age, sometimes in conjunction with demonstrating preparation. Most modern societies determine legal adulthood based on reaching a legally specified age without requiring a demonstration of physical maturity or preparation for adulthood. ==Biological adulthood== Historically and cross-culturally, adulthood has been determined primarily by the start of puberty (the appearance of secondary sex characteristics such as menstruation in women, ejaculation in men, and pubic hair in both sexes). In the past, a person usually moved from the status of child directly to the status of adult, often with this shift being marked by some type of coming-of-age test or ceremony. After the social construct of adolescence was created, adulthood split into two forms: ''biological adulthood'' and ''social adulthood.'' Thus, there are now two primary forms of adults: biological adults (people who have attained reproductive ability, are fertile, or who evidence secondary sex characteristics) and social adults (people who are recognized by their culture and/or law as being adults). Depending on the context, ''adult'' can indicate either definition. Although few or no established dictionaries provide a definition for the two word term biological adult, the first definition of adult in multiple dictionaries includes "the stage of the life cycle of an animal after reproductive capacity has been attained".〔''International Dictionary of Medicine and Biology'' (1986)〕〔''Churchill’s Medical Dictionary'' (1989)〕 Thus, the base definition of the word adult is the period beginning at puberty. Although this is the primary definition of the base word adult, the two word term ''biological adult'' stresses or clarifies that the original definition, based on the beginning of puberty, is being used. Puberty generally begins around 10 or 11 years of age for girls and 11 or 12 years of age for boys, though this will vary from person to person.〔(Chumlea, 1982).〕〔"For girls, puberty begins around 10 or 11 years of age and ends around age 16. Boys enter puberty later than girls-usually around 12 years of age-and it lasts until around age 16 or 17." 〕 Because the term adult is most often used without the adjective social or biological, and since the term is frequently used to refer to social adults, some writers have taken the meaning of the two word phrase biological adult to begin at the end of physical maturation rather than the onset of puberty. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「adult」の詳細全文を読む スポンサード リンク
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