Two sociologists argue that blonde women are inherently more attractive than non-blonde women, because blonde hair is a biological marker of youth. The book is called Why Beautiful People Have More Daughters by Alan S. Miller and Satoshi Kanazawa, and an excerpt was featured in a Psychology Today article in 2007. Here is part of the excerpt:
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.
Light-coloured hair among children is a characteristic of Europeans, and is not universal. Babies of Asian and African descent almost always have black hair.
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.
Since light-coloured hair among youth is not universal among humans, the argument that heterosexual male humans are attracted to blondes because of genetics is absurd. Have Asian and African men evolved to prefer blondes as well? How would this occur, if blond hair was a rather late mutation in human evolution, confined to Northern Europe? Light-coloured hair in non-Caucasian Asian and African populations before contact with Northern European genes were markers of albinism.
However, perhaps the authors were not making this argument, and were merely arguing that contemporary males find blonde females more attractive because blonde hair is still correlated with youth, among Caucasians. That is, perhaps contemporary heterosexual males see or meet a large sample of Caucasians throughout their lives, and unconsciously extrapolate the correlation between blonde hair and youth. Perhaps the blonde-youth correlation is a result of exposure to Caucasians, rather than hard-wired. This interpretation is more reasonable, given that the authors were trained in sociology rather than biology.
Unfortunately, the full title of the book is Why Beautiful People Have More Daughters: From Dating, Shopping, and Praying to Going to War and Becoming a Billionaire– Two Evolutionary Psychologists Explain Why We Do What We Do and is an evolutionary psychology book.