所有200种左右的灵长类动物都有黑色的眼睛和几乎不可见的巩膜。

All 200 or so species of primates have dark eyes and a barely visible sclera.

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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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康沃耳利斯卡德附近的Commonmoor，这只白化乌鸫雏鸟清晰可见的红眼睛与白化病有关，因为眼睛里缺少一种色素。

This albino blackbird chick at Commonmoor near Liskeard in Cornwall clearly shows the red eyes often associated with albinism due to a lack of pigment in the eyes

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