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在青春期，次級性徵開始出現，它是性激素刺激的結果。女性的次級性徵出現得早，男性則比較晚。到了男女都發育成熟的時候，男性身體和女性身體顯露出數個特徵性的差別。

青春期的變化可能非常緩慢地發生直到度過十多年的時光，或者這種變化忽然出現，而且就在1年或兩年的光景就完成了變化。一般來說，現今的青年人比他們的爺爺奶奶或爺爺奶奶的爺爺奶奶們要較早體驗青春期的變化。確確實實，在過去的100年裏，世界大多數地區，青春期開始的年齡一直在穩步地降低。社會環境和膳食結構的改變可能在這種變化中扮演了主要的角色。不管怎樣說，青春期賦予了男孩和女孩“典型“成年人的體貌。然而，人類是一種多種族的生物，而且具有地域的差異。例如，亞洲男人比歐洲男人的肌肉纖弱和體毛稀少。

Development of secondary sexual characteristics

The secondary sexual characteristics begin to appear during puberty as a result of hormonal stimulation. They become apparent first in females, a little later in males. By the time their physical growth is completed, the bodies of men and women show several marked differences.

The changes of puberty may occur very slowly and extend over a period of more than a decade, or they may appear rather suddenly and be completed within one or two years. In general, young people today experience the changes earlier than their grandparents or great-grandparents. Indeed, within the last hundred years, the age of puberty has been steadily lowering in most parts of the world. Changing social conditions and changing diets may play a role in this development. In any case, puberty gives female and male bodies their "typical" adult appearance. However, humans are a varied species, and there are regional differences. For example, Asian men usually remain less muscular and develop less facial and body hair than European men.