[21]　一个“切达人”已经拥有了“深到近乎黑色的皮肤”：‘First Modern Britons Had “Dark to Black” Skin', Guardian,7 Feb. 2018.
[22]　用于进行分析的DNA分解得太厉害：New Scientist, 3 March 2018, p. 12.
[23] 我们其实跟猿类表亲们一样毛发丛生：Jablonski, Skin, p. 19.
[24] 我们估计有500万根毛发：Linden, Touch, p. 216.
[25]　能提供保暖、缓冲和伪装：It provides warmth, cushioning, and camouflage: ‘The Naked Truth', Scientific American, Feb. 2010.
[26]　哺乳动物有毛，使得毛发和皮肤之间增加了一层有用的绝缘空气：Ashcroft, Life at the Extremes, p. 157.
[27]　鸡皮疙瘩也能让哺乳动物的毛发直立：Baylor University Medical Center Proceedings, July 2012, p. 305.