translation.en: In "The Descent of Man," he wrote, "In each great region of the world, the living mammals are closely related to the extinct species of the same region.
translation.zh: 在他的书“人类的起源”中，他写道： “在世界的每个区域，现存的哺乳动物 都和同一区域灭绝的物种紧密相连。