这种情况就是说黑色素细胞因遭到免疫系统攻击而变得虚弱，从而无法产生黑素。
There is an autoimmune condition called vitiligo in which melanocytes are attacked by the immune system and become too weak to produce melanin.
实力虚弱者会避免引发一场不能取胜的争斗，攻击性强者在没有受伤风险的情况下可以因此而取胜。
Potential victims avoid starting fights they cannot win, while the aggressive get their way without risking injury.
大约二百万年以前，我们虚弱而且易受攻击的祖先居住着山洞里，他们面临大自然的严峻考验，很容易生病。
About 2 million years ago, our feeble and bulnerable (susceptable) ancestors dwelled in the cavities and they were exposed to grim hardships in nature so as to be prone to diseases.
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