People often kill each other. In wars, millions of people may be killed by other humans. But animals rarely kill their own kind. Male wolves, for example, may have a bloody fight to decide who will lead the pack. But the loser just lies down on his back and surrenders. The loser is not killed.

人类经常会互相残杀。在战争中，数以百万计的人有可能被他人杀掉。但动物很少会杀死自己的同类。比如，公狼可能要靠一场惨烈的打斗来决定谁是领头，可失败的狼也只是躺倒投降。输掉的狼不会被杀。