What accounts for the markedly lower average level of physical attractiveness among black women? Black women are on average much heavier than nonblack women. The mean body-mass index (BMI) at Wave III is 28.5 among black women and 26.1 among nonblack women. (Black and nonblack men do not differ in BMI: 27.0 vs. 26.9) However, this is not the reason black women are less physically attractive than nonblack women. Black women have lower average level of physical attractiveness net of BMI. Nor can the race difference in intelligence (and the positive association between intelligence and physical attractiveness) account for the race difference in physical attractiveness among women. Black women are still less physically attractive than nonblack women net of BMI and intelligence. Net of intelligence, black men are significantly more physically attractive than nonblack men.
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The only thing I can think of that might potentially explain the lower average level of physical attractiveness among black women is testosterone. Africans on average have higher levels of testosterone than other races, and testosterone, being an androgen (male hormone), affects the physical attractiveness of men and women differently. Men with higher levels of testosterone have more masculine features and are therefore more physically attractive. In contrast, women with higher levels of testosterone also have more masculine features and are therefore less physically attractive. The race difference in the level of testosterone can therefore potentially explain why black women are less physically attractive than women of other races, while (net of intelligence) black men are more physically attractive than men of other races.

http://www.huffingtonpost.com/2011/05/17/satoshi-kanazawa-black-women-less-attractive_n_863327.html