Differences among groups of people have been noticed since antiquity. The Greek Philosopher Herodotus (484-425 B.C.) travelled over thousands of miles and recorded his observation of languages, religions, ways of life, laws and government of different people.
Biblical theologists imagined the origin of exotic peoples back in some mythical episode like the dispersion of the three sons of Noah (Sem, meaning ``famous'' went on to Asia and built Salem (Jerusalem); Japheth, meaning ``liberty and freedom'' went on to rule Europe; and Cham, meaning ``subtlety and craft'', though cursed by his father, was allowed to rule Egypt) .
See http://www.write-on.co.uk/history/travels_of_noah.htm for a review of ``The Travels of Noah into Europe'', publ. 1601.
... Or considered dark-skinned people to be the offspring of Adam's banished (to the East!) son Cain whose face had been covered in darkness. American Indians or Arabian nomads were thought to be a ``corrupt'' or ``degenerate'' form in contrast to the ``pure strains'' of white Europeans who were descended directly from Adam or Abraham. In Indian mythology too there are stories about races descended from gods and of the origins of various minor castes.