“在进化过程中，因为人体必须承受这些微生物，以此激活人体免疫系统的承受能力，”Rook说。

"What has happened over the course of evolution is, because these bugs had to be tolerated, they came to activate the tolerance of the immune system, " Rook said.

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一般对这一问题的回答是：大多数的太阳光都是可见光，所以我们的眼睛在进化过程中已经形成了选择性偏好。

The traditional answer to this question was that most of the sun's radiation is visible light, so our eyes evolved to see those wavelengths.

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一些具有差异化的表现形式但对功能影响不大的特征- - -比如头盖骨的形状，在进化过程中可能起着比自然选择更重要的作用。

With features that can vary somewhat in form without greatly affecting function, such as the shape of the skull, chance might play a bigger role in their evolution than natural selection.

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