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A boy is a young malehuman. The term is usually used for a child or an adolescent. When a male human reaches adulthood, he is described as a man.
Definition, etymology, and use
According to the Merriam-Webster Dictionary, a boy is "a male child from birth to adulthood".
The word "boy" comes from Middle Englishboi, boye ("boy, servant"), related to other Germanic words for boy, namely East Frisianboi ("boy, young man") and West Frisianboai ("boy"). Although the exact etymology is obscure, the English and Frisian forms probably derive from an earlier Anglo-Frisian *b?-ja ("little brother"), a diminutive of the Germanic root *b?- ("brother, male relation"), from Proto-Indo-European *bh?-, *bh?t- ("father, brother"). The root is also found in Norwegian dialectalboa ("brother"), and, through a reduplicated variant *b?-b?-, in Old Norsebófi, Dutchboef "(criminal) knave, rogue", GermanBube ("knave, rogue, boy"). Furthermore, the word may be related to B?ia, an Anglo-Saxon personal name.
Poor Neapolitan children
Tanzanian boy transporting fodder
Historically, in the United States and South Africa, "boy" was not only a "neutral" term for domestics but also a disparaging term towards black men; the term implied a subservient status. Thomas Branch, an early African-American Seventh-day Adventist missionary to Nyassaland (Malawi) referred to the native students as "boys":
There is one way by which we judge many of our present boys to be quite different from some of those who were here long ago: those that are married have their wives here with them, and build their own houses, and all are busy making their gardens. I have told all the boys that if they wished to stay here and learn, those that had wives must bring them.
Multiple politicians - including New Jersey Governor Chris Christie and former Kentucky Congressman Geoff Davis - have been criticized publicly for referring to a black man as "boy."
Some boys defy traditional gender expectations. Boys who do so may face social stigma from parents  and peers.  Boys who defy gender norms face a higher risk of abuse, and may experience more depression than gender-conforming peers.  Gender-expansive[a] and transgender boys can face bullying and pressure to conform to traditional expectations. Some intersex children and some transgender children who were assigned female at birth may self-identify as boys.
Human sex is determined at fertilization when the geneticsex of the zygote has been initialized by a spermcell containing either an X or Y chromosome. If this sperm cell contains an X chromosome, it will coincide with the X chromosome of the ovum and a girl will develop. A sperm cell carrying a Y chromosome results in an XY combination, and a boy will develop.
In male embryos at six to seven weeks' gestation, "the expression of a gene on the Y chromosome induces changes that result in the development of the testes". At approximately nine weeks' gestation, the production of testosterone by a male embryo results in the development of the male reproductive system.
Puberty is the process by which children's bodies mature into adult bodies that are capable of reproduction. On average, boys begin puberty at ages 11-12 and complete puberty at ages 16-17.
In boys, puberty begins with the enlargement of the testicles and scrotum. The penis also increases in size, and a boy develops pubic hair. A boy's testicles also begin making sperm. The release of semen, which contains sperm and other fluids, is called ejaculation. During puberty, a boy's erect penis becomes capable of ejaculatingsemen and impregnating a female. A boy's first ejaculation is an important milestone in his development. On average, a boy's first ejaculation occurs at age 13. Ejaculation sometimes occurs during sleep; this phenomenon is known as a nocturnal emission.
When a boy reaches puberty, testosterone triggers the development of secondary sex characteristics. A boy's muscles increase in size and mass, his voice deepens, his bones lengthen, and the shape of his face and body changes. The increased secretion of testosterone from the testicles during puberty causes the male secondary sexual characteristics to be manifested. Male secondary sex characteristics include:
^The source defines gender-expansive as: "Children who do not conform to their culture's expectations for boys or girls. Being transgender is one way of being gender-expansive, but not all gender-expansive children are transgender."
^Differences, Institute of Medicine (US) Committee on Understanding the Biology of Sex and Gender; Wizemann, Theresa M.; Pardue, Mary-Lou (November 28, 2001). "Sex Begins in the Womb". National Academies Press (US) – via www.ncbi.nlm.nih.gov.
Allen, Edward A. (1982). "Public School Elites in Early-Victorian England: The Boys at Harrow and Merchant Taylors' Schools from 1825 to 1850". Journal of British Studies. 21 (2): 87-117. doi:10.1086/385791.
Liu, Fengshu (2006). "Boys as only-children and girls as only-children--parental gendered expectations of the only-child in the nuclear Chinese family in present-day China". Gender and Education. 18 (5): 491-505. doi:10.1080/09540250600881626.
Powell, Sacha; Smith, Kate, eds. (2017). An introduction to early childhood studies. Sage. from a variety of disciplines and international perspectives.
Rose, Clare (2016). Making, selling and wearing boys' clothes in late-Victorian England. Routledge.
Theriault, Daniel (2018). "A Socio-Historical Overview of Black Youth Development in the United States for Leisure Studies". International Journal of the Sociology of Leisure. 1 (2): 197-213. doi:10.1007/s41978-018-0013-y.
Wainman, Ruth (2017). "'Engineering for Boys': Meccano and the Shaping of a Technical Vision of Boyhood in Twentieth-Century Britain". Cultural and Social History. 14 (3): 381-396.
Wolff, Larry (1996). "The Boys Are Pickpockets, and the Girl Is a Prostitute": Gender and Juvenile Criminality in Early Victorian England from Oliver Twist to London Labour". New Literary History. 27 (2): 227-249. JSTOR20057349.