性-人类性的基本层面
Sex - Basic Aspects of Human Sexuality

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次级性征的发育

在青春期，次级性征开始出现，它是性激素刺激的结果。女性的次级性征出现得早，男性则比较晚。到了男女都发育成熟的时候，男性身体和女性身体显露出数个特征性的差别。

青春期的变化可能非常缓慢地发生直到度过十多年的时光，或者这种变化忽然出现，而且就在1年或两年的光景就完成了变化。一般来说，现今的青年人比他们的爷爷奶奶或爷爷奶奶的爷爷奶奶们要较早体验青春期的变化。确确实实，在过去的100年里，世界大多数地区，青春期开始的年龄一直在稳步地降低。社会环境和膳食结构的改变可能在这种变化中扮演了主要的角色。不管怎样说，青春期赋予了男孩和女孩“典型“成年人的体貌。然而，人类是一种多种族的生物，而且具有地域的差异。例如，亚洲男人比欧洲男人的肌肉纤弱和体毛稀少。

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.