If 90% of the people on this planet sport the usual primate pattern of dark hair and dark eyes, then why do some people come in paler shades?
Consider a simple experiment:
Place a photo of a fair skinned redhead with blue eyes among 3 photos of brunettes who have darker skin and brown eyes. Place that same redhead among larger crop of brunettes. Is the same woman rated more attractive when she's seen with a larger number of brunettes?
Yes, that's exactly what happened when Thomas Thelen conducted the experiment. He found the reverse too - when the brunette was rare, she was more attractive.
Sexual selection, in addition to natural selection, provides a mechanism by which organisms can change over time. Sexual selection involves two parts: 1) outcompeting same-sex rivals for mates and 2) being selected as a mate - often in that order.
So, what's exotic is erotic.
A Persian immigrant in a sea of Scandanavian blonds will be able to attract attention away from her fair haired rivals, all other things being equal.
Those other things?
Healthy skin & hair, symmetrical face and body, hourglass shape, and - KINDNESS!
For all of the EP talk about the importance of physical beauty for women in the mating game, we rarely hear about personality.
Personality goes a long way.
What do you think this "rarity principle" has to say about the evolution of personality?