Onset of Puberty
Puberty is a short-term event of the central nervous system, which re-initiates positive feedback within the hypothalamic-pituitary-gonadal (HPG) axis and promotes sexual maturation. In the anthropoid primates, sexual maturation proceeds during fetal and early post-natal life, but then the HPG axis is dominated by negative feedback during the juvenile life history stage. The negative feedback delays or suspends sexual maturation for months or years. In humans, the negative feedback begins at about two years after birth. At about nine years of age the HPG axis reverts to positive feedback. The chimpanzee seems to follow a similar age pattern of negative feedback, but re-initiates positive feedback between 6-7 years of age. In most species of primates, puberty is followed within a few months or a year by reproduction. Chimpanzee females in captivity have first birth at about 9 years of age, showing a delay of two years from puberty. In the wild the delay is longer (average first birth at age 13 years). In humans, there is a greater delay between puberty and first reproduction, usually on the order of 5 to 10 years. This is the human adolescent growth stage.
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