]Alan S. Miller Ph.D., Satoshi Kanazawa Ph.D.
Blond hair is unique in that it changes dramatically with age. Typically, young girls with light blond hair become women with brown hair. Thus, men who prefer to mate with blond women are unconsciously attempting to mate with younger (and hence, on average, healthier and more fecund) women. It is no coincidence that blond hair evolved in Scandinavia and northern Europe, probably as an alternative means for women to advertise their youth, as their bodies were concealed under heavy clothing.