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10/29/2007: "BadScience.net commits bad science"

Oliver has perhaps not been to Brazil, where black African, white European, and Amerindian have lived side by side and bred together for many centuries. The Brazilians have not gone coffee coloured, they in fact still show a wide range of skin pigmentation, from black to tan. This is because skin pigmentation seems to be coded for by a fairly small number of genes and probably doesn.t blend and even out as Oliver - a political theorist, not a scientist - suggests.

http://www.badscience.net/?p=316

Skin reflectance was measured on the inner upper arm and forehead of a sample of 209 Mestizos ranging in age from 2 to 64 years living in the town of Lamas in the Eastern Peruvian Lowlands. The sample consisted of 43 father-son, 42 father-daughter, 62 mother-son, and 70 mother-daughter pairs. The sample also consisted of 57 brother-brother, 60 sister-sister and 139 brother-sister pairs. The reflectance measurements were made with a Photovolt Reflection Meter, model 670. Stepwise polynomial regression techniques were used to derive standardized residual values. Then using these residual values parent-offspring, sibling intraclass correlations and components of the phenotypic expression of skin reflectance were calculated. The study indicates that 1) the parent-offspring and sibling correlation coefficients conformed with the theoretical correlations expected assuming polygenic inheritance; 2) the husband-wife correlations indicate a high degree of assortative mating for skin color, but despite this effect the parent-offspring and sibling correlation coefficients are lower than the values expected under the influence of autosomal genes; 3) estimates of heritability and components of phenotypic expression indicate that about 55% of the total variability in skin reflectance could be attributed to the influence of additive genetic factors; and 4) there is no evidence of X-linkage in the inheritance of skin color.

http://www3.interscience.wiley.com/cgi-bin/abstract/110483224/ABSTRACT?CRETRY=1&SRETRY=0

[ Skin color is mostly determined by degree of mixture, in contrast to what the bad science guy says. Further, the bad science guy's assumption is that ethnic mixing was mathematically uniform, for which there's no evidence and plenty of counter-evidence, given the "racism" (preference for breeding among one's genetic proximates) we hear decried in Brazil. ]