From Nietzsche's Daybreak , Book IV, Aphorism 241:
Fear and intelligence . - If it is true, as is now most definitely asserted,
that the cause of black skin pigmentation is not to be sought in the
action of light, could it perhaps not be the ultimate effect of frequent
attacks of rage (and undercurrents of blood beneath the skin)
accumulated over thousands of years? While with the other, more
intelligent races an equally frequent terror and growing pallid has
finally resulted in white skin? - For degree of timidity is a measure of
intelligence, and frequently to give way to blind rage a sign that
animality is still quite close and would like to take over again. - Thus
the original colour of man would probably have been a brownish
grey - somewhat like the ape and the bear, as seems proper.
This must not be dismissed out of hand...