Race and physical attractiveness
The relationship between race and physical attractiveness have between investigated in empirical research and analyzed in theoretical arguments.
National Longitudinal Study of Adolescent Health
The National Longitudinal Study of Adolescent Health (Add Health) is "a longitudinal study of a nationally representative sample of adolescents in grades 7-12 in the United States during the 1994-95 school year. The Add Health cohort has been followed into young adulthood with four in-home interviews, the most recent in 2008, when the sample was aged 24-32". Among other variables it has measured the physical attractiveness of the participants. 3 different interviewers have rated the physical attractiveness of each participant on 3 different occasions over 7 years.
Psychologist Satoshi Kanazawa in a 2011 article analyzed the data. Women were generally more physically attractive than men. White men and White women were rated the most physically attractive. The statistically significant racial difference was the lower physically attractiveness for Black women than for other women. The average results for the different races and sexes are presented below with 0 as the average result for the whole group and 1 as one standard deviation. Higher values indicate higher physical attractiveness.
- Men: White -0.17, Black -0.23, Asian -0.19, Native American -0.31
- Women: White 0.23, Black -0.04, Asian 0.19, Native American 0.15
In contrast, when the participants were asked to judge their own individual physical attractiveness, both Black men and Black women rated themselves as far more physically attractive than men and women of other races. The self-reported average physical attractiveness score for Blacks were about double those of other races.
Kanazawa argued that the White and Black men in the studied group did not differ significantly on BMI which is a measure of obesity. Black and White women differed somewhat with average BMIs of 28.5 and 26.1. However, the Black women were still less physically attractive after controlling for this difference.
Higher IQ has a relationship with higher physical attractiveness which could be an explanation due to the differences regarding race and intelligence. However, Black women were still less physically attractive after controlling for both BMI and intelligence. On the other hand, after controlling for intelligence, Black men were significantly more attractive than non-Black men.
Kanazawa argued that Africans have higher levels of testosterone than other races. Persons with higher levels of testosterone have higher levels of masculine features which may make men more physically attractive but women less so. This would explain the generally lower physical attractiveness of Black women and the higher physical attractiveness of Black men after controlling for intelligence. See also Other race differences: Femininity vs. masculinity.
The not politically correct article caused a firestorm of outrage. The article was retracted. The largest student organization in London demanded that Kanazawa should be fired. Various scientific criticisms were also raised.
An analysis of data on replies to contact attempts on the OKCupid dating service stated among other results that "Black women reply the most, yet get by far the fewest replies. Essentially every race—including other blacks—singles them out for the cold shoulder", "White women prefer white men to the exclusion of everyone else—and Asian and Hispanic women prefer them even more exclusively. These three types of women only respond well to white men. More significantly, these groups’ reply rates to non-whites is terrible", and " Whatever it is, white males just get more replies from almost every group." However, the examined groups had been selected to have equal physical attractiveness as determined by a "picture-rating utility" which may have ruled out physical attractiveness as an explanation except for the possible effect of skin color.
Several other studies of dating services have found a strong preference for white males on the part of white females. According to a 2011 study by Gerald Mendelsohn on over a million dating website profiles "more than 80 percent of the online dating contacts initiated by whites were to other whites, with only 3 percent going to blacks. This trend held for both men and women, young and old. Although black participants initiated contact to members of their own race more than to whites, they were ten times more likely to contact whites than vice versa, according to the study."  Another massive study of online daters found that "Over 90% of white women who state a racial preference prefer not to date East Indians, Middle Easterners, Asians, and blacks. White men with stated racial preferences, in contrast, only prefer not to date one group at levels above 90%: black women." Furthermore, "One of the most striking findings is that white women who describe themselves as slim, slender, athletic, fit or average are nearly seven times as likely to exclude black men as dates as women who describe themselves as thick, voluptuous, a few extra pounds, or large." 
Studies of speed dating events have found similar results. According to a 2006 study, "Women strongly discriminate on the basis of race. They are more than 14 percentage points more likely to accept a partner of their own race. Given the underlying Yes Rate of 38 percent, this is a large effect. Men, on the other hand, do not exhibit a significant racial preference."  Another study found "While men at HurryDate events are strongly attracted to women who are thin, young, attractive, and of a similar race, women strongly prefer men who are physically attractive, tall, young, of medium build, and of a similar race. Women’s preferences are not strongly determined by a single trait, but, collectively, their preferences are driven by appearance." 
Skin color and facial studies
Several studies have examined reactions to differences in skin color and facial features. Some have used opinion surveys. Others have examined how facial photographs are rated for physical attractiveness. Such studies may be less affected by other factors such as differences in intelligence or personality that may be demonstrated by the subject in an interview situation such as in the National Longitudinal Study of Adolescent Health.
A 1978 survey of 1000 White college students found that "Males indicated somewhat greater preference for lighter female coloration, while females indicated somewhat greater preference for darker male coloration".
A 1986 study using a cross-cultural survey found that lighter skin was more strongly preferred for women than for men in all culture areas.
A 2004 study by T. Joel Wade found drawings of faces with white characteristics were rated significantly more attractive than black male faces by a group of 38 white females and 5 black females.  A 2008 study by the same researcher, looking at female facial attractiveness by males found Asian female faces to be least attractive, white female faces most attractive and black female intermediate.
A 2011 study examined the ratings of photographs of Black, White, and mixed-race faces. White females faces were rated the most attractive as were Black male faces. White skin color increased attractiveness for females as did black skin color for males. These results were somewhat different from earlier studies were, while a somewhat darker male complexion was preferred, this was only relative to the local population so that the darkest male complexion was not seen at the most attractive. It has been suggested that this extreme preference for Black male faces, even stated by White males, was influenced by increasing political correctness. In the paper, Lewis admits that "One explanation for the results found in the current experiment is that they represent an over-compensation as a result of prejudice avoidance. The participants may wish to avoid appearing prejudiced and so rate other-race faces as being more positive." According to Peter Frost "Because the white British participants had to choose among very divergent skin colors, their responses were almost certainly contaminated by ‘prejudice avoidance’, i.e., they avoided giving low ratings to non-white faces for fear of seeming prejudiced. Since anti-white prejudice is not stigmatized, the tendency would be to overcompensate—to err on the safe side." This same study found white males rated "mixed-race" females higher than white females, and a statistically insignificant difference between ratings of black and white females, further suggesting the influence of political correctness
A 2012 study examined facial attractiveness for Whites, Black, and East Asians. For females the East Asian faces were rated the most attractive while for males the Black faces were rated the most attractive. An observation here is that East Asians do not have the whitest skin color. As for the 2011 study, there is the possibility of increasing political correctness affecting the results.
Both of these studies (by Michael B. Lewis) suffer from very small sample sizes and poor experiment design.
These differences in physical attractiveness may explain differences in interracial marriages such as Black men much more often marrying White and Chinese women than Black women marrying White and Chinese men as well as White men much more often marrying Chinese women than White women marrying Chinese men.
Skin whitening products
In many countries skin whitening products are very popular among women despite sometimes containing toxic ingredients such as mercury. For example, the World Health Organization in 2012 stated that in India 61% of the dermatological market consisted of skin lightening products with mercury being a common ingredient.
A politically correct explanation for preference for whiter skin color in women is that White women are favored as the beauty ideal in various media such as advertising and movies. However, this preference may also be explained as the media having to adapt to what their consumers actually prefer. The politically correct explanation have difficulty explaining why (somewhat) darker skin in men have been seen as more attractive in the studies mentioned above.
In the same race females have somewhat lighter skin color than males. Skin color is thus one of the sexually differentiating characteristics. This may explain why (somewhat) whiter females are seen as more attractive as are (somewhat) darker males (if intelligence is controlled for).
There are several theories regarding the evolutionary origins of the racial differences in skin color and facial features. One starts with the argument that survival in colder climate was more difficult which caused females to be more dependent on males for support than in warmer climates. Consequently, in colder climates there would be relatively more competition for males among females. This would favor the evolutionary development of characteristics which males would find preferable. This evolution would to some degree affect both sexes. In Europeans this is argued to have contributed to the development of whiter skin color and in East Asians to the development of more feminine facial features. The opposite is argued to have occurred in warmer climates.
Another approach focuses on the health effect of skin color. Darker skin may protect against skin cancers from sunlight exposure, sunstroke, and folate degradation to toxic products due to ultraviolet radiation. These factors would favor a darker skin near the equator. On the other hand, vitamin D can be gained from food sources but is also metabolized in the skin with the help of sunlight. This process is helped by a lighter skin color. This could explain why populations generally have a lighter skin color the further they are from the equator. However, this does not explain why Europeans have whiter skins than other populations that live equally far from the equator. An explanation for this is that Europeans after the introduction of agriculture received relatively little vitamin D from animal food sources which would have made metabolism using sunlight more important. This theory would mean that the white skin of Europeans is a relatively new development that occurred after the introduction of agriculture in Europe. This is supported by research finding that the light skin of Europeans developed as short time as 3.000 to 12.000 years ago.
- Add Health. Carolina Population Center. University of North Carolina . http://www.cpc.unc.edu/projects/addhealth
- Satoshi Kanazawa. Why Are Black Women Less Physically Attractive Than Other Women? May 15, 2011. Psychology Today. http://www.quora.com/What-makes-Why-Are-Black-Women-Less-Physically-Attractive-Than-Other-Women-unscientific
- Scott Barry Kaufman and Jelte Wicherts. Black Women Are Not (Rated) Less Attractive! Our Independent Analysis of the Add Health Dataset. May 21, 2011. Psychology Today. http://www.psychologytoday.com/blog/beautiful-minds/201105/black-women-are-not-rated-less-attractive-our-independent-analysis-the-a
- Khadijah Britton. The Data Are In Regarding Satoshi Kanazawa. May 23, 2011. Scientific American. http://blogs.scientificamerican.com/guest-blog/2011/05/23/the-data-are-in-regarding-satoshi-kanazawa/
- Criminal Victimization in the United States, 2008. Bureau of Justice Statistics. http://www.bjs.gov/content/pub/pdf/cvus08.pdf
- How Your Race Affects The Messages You Get, October 5th, 2009 by Christian Rudder, http://blog.okcupid.com/index.php/your-race-affects-whether-people-write-you-back/
- In Online Dating, Blacks More Open to Romancing Whites Than Vice Versa, Study Finds February 12, 2011 Science Daily, http://www.sciencedaily.com/releases/2011/02/110211183853.htm
- Gendered Racial Exclusion among White Internet Daters, 2006, Cynthia Feliciano et. al, http://paa2008.princeton.edu/papers/80046
- GENDER DIFFERENCES IN MATE SELECTION:EVIDENCE FROM A SPEED DATING EXPERIMENT, 2006, Fisman et. al, http://qje.oxfordjournals.org/content/121/2/673.full.pdf
- HurryDate: Mate preferences in action, 2004, Kurzban & Weeden, http://www.sas.upenn.edu/psych/PLEEP/pdfs/2005%20Kurzban%20&%20Weeden%20EHB.pdf
- Feinman, Saul; Gill, George W.. Sex differences in physical attractiveness preferences. The Journal of Social Psychology, Vol 105(1), Jun 1978, 43-52. http://psycnet.apa.org/doi/10.1080/00224545.1978.9924089
- Peter Frost. Sex, ethnicity, and facial skin perception. Sunday, December 10, 2010. Evo and Proud. http://evoandproud.blogspot.se/2010/12/sex-ethnicity-and-facial-skin.html
- Wade, T. Joel et. al Racial characteristics and individual differences in women's evaluations of men's facial attractiveness and personality http://www.sciencedirect.com/science/article/pii/S0191886903002022
- Michael B. Lewis, Who is the fairest of them all? Race, attractiveness and skin color sexual dimorphism, Personality and Individual Differences, Volume 50, Issue 2, January 2011, Pages 159-162, ISSN 0191-8869, http://dx.doi.org/10.1016/j.paid.2010.09.018.
- Michael B. Lewis. A Facial Attractiveness Account of Gender Asymmetries in Interracial Marriage. PLoS One. 2012; 7(2): e31703. Published online 2012 February 9. http://dx.doi.org/10.1371/journal.pone.0031703
- Kounteya Sinha. WHO warns against mercury-laced cosmetics. Times of India. Jun 5, 2012. 04.30AM http://articles.timesofindia.indiatimes.com/2012-06-05/health/32055036_1_mercury-salts-creams-soaps
- The evolution of different skin colours. Arnfinn Hykkerud Steindal and Johan Moan. Solar Radiation and Human Health. Espen Bjertness, editor. The Norwegian Academy of Science and Letters, 2008. http://www.dnva.no/geomed/solarpdf/Nr_9_Hykkerud_Stendal.pdf