Psychology Today has an excerpt from the book Why Beautiful People Have More Daughters, by Alan S. Miller and Satoshi Kanazawa, which explores "Ten Politically Incorrect Truths About Human Nature," including the mystery of the "blonde bombshell":
Long before TV—in 15th- and 16th- century Italy, and possibly two millennia ago—women were dying their hair blond. Women's desire to look like Barbie—young with small waist, large breasts, long blond hair, and blue eyes—is a direct, realistic, and sensible response to the desire of men to mate with women who look like her. There is evolutionary logic behind each of these features.The article also explains why men prefer women with small waists and large breasts (both are correlated with levels of estrogen and progesterone, indicating greater fecundity), why beautiful people have more daughters (physical attractiveness is more important for girls than boys, and parents can bias the sex ratio depending on the traits they can offer), why men sexually harass women (it's about respect), and why most suicide bombers are Muslim (the 72 virgins waiting patiently in heaven aren't trivial). Some of the hypotheses are a little dubious to me, but it's an interesting read nonetheless.
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.
Women with blue eyes should not be any different from those with green or brown eyes. Yet preference for blue eyes seems both universal and undeniable—in males as well as females. One explanation is that the human pupil dilates when an individual is exposed to something that she likes. For instance, the pupils of women and infants (but not men) spontaneously dilate when they see babies. Pupil dilation is an honest indicator of interest and attraction. And the size of the pupil is easiest to determine in blue eyes. Blue-eyed people are considered attractive as potential mates because it is easiest to determine whether they are interested in us or not.
The irony is that none of the above is true any longer. Through face-lifts, wigs, liposuction, surgical breast augmentation, hair dye, and color contact lenses, any woman, regardless of age, can have many of the key features that define ideal female beauty. And men fall for them. Men can cognitively understand that many blond women with firm, large breasts are not actually 15 years old, but they still find them attractive because their evolved psychological mechanisms are fooled by modern inventions that did not exist in the ancestral environment.
Link to the article.