The use of the word "Caucasian" to denote the "race" of
Europeans and those of European ancestry dates to the late 18th century, when
German naturalist Johann Friedrich Blumenbach wrote
On the Natural Variety of Mankind, dividing the human species into five races: Caucasian, Mongolian, Ethiopian, American, and Malay.
Blumenbach declared that Europeans were the most beautiful people in the world, and that the most beautiful Europeans were to be found in the Caucasus mountains of what is now Georgia. His racial categorizations were based on skull measurements, however, rather than skin color, a fact which seriously undermines the validity of using Caucasian as a synonym for "white." The skull that led him to his questionable epiphany had been of a woman from the Caucusus region.
Blumenbach believed that the human species had begun in the Caucusus as well. His reasoning, which eludes my comprehension, led him to conclude that the location of the most aesthetically appealing (to him) humans must also be that of the species' origin.