形成头发颜色差异的根本原因是在于人类的进化和遗传因素，这与肤色不同的道

形成头发颜色差异的根本原因是在于人类的进化和遗传因素，这与肤色不同的道理是一样的。因为，黄种人长期生活在阳光充足的热带和亚热带地区，较强的紫外线照射使用权欠祖先的皮肤及毛发中黑色素含量增多，以对自身进行保护。这样，一代一代地遗传下来，头发就是黑色的了。

西方人多生活在目光稀少的寒带地区，紫外线较少，皮肤和毛发内黑色素含量较少，久而久之便形成了金黄色的头发。这是人类进化、适应自然的结果。

結果 (中文) 3:

The root cause of the hair color difference is that human evolution and genetic factors, which is different from the color of the truth is the same. Because the yellow people long-term living in sunny tropical and subtropical regions, increase the melanin content of skin and hair strong ultraviolet radiation under the right to the use of ancestors, in order to protect their own. In this way, generation by generation, the hair is black.Westerners living in the eyes of rare cold regions and less UV, melanin content of skin and hair less, in the course of time will form a golden yellow hair. This is the result of human evolution and adaptation to nature.