[kridsdale1]

Some of us have partially evolved for that environment. My ancestors eyes turned blue to see in the dim light and their hair and skin changed from Ethiopian Black to pale and blonde af.

Seems reasonable to expect some degree of genetic drift in sleep regulation as well, but I know of no data on this.

[absolutelastone]

A bigger pupil would work better for dim light vision. Light through the iris would sacrifice daylight vision. The light skin on the other hand does have an obvious benefit in that climate for Vitamin D.