Eye color for a plausible argument stating that some eyes can or do change, based on chemical reactions and hormonal changes within the body. Studies on Caucasian twins, both fraternal and identical, have shown that eye color over time can be subject to change, and major demelanization of the iris may also be genetically determined. Most eye-color changes have been observed or reported in the Caucasian population with hazel and amber eyes. Carleton Coon created a chart by the original Martin scale. The numbering is reversed on the scale below in the (later) Martin–Schultz scale, which is (still) used in physical anthropology.
Neoteny in humans and the Red Queen hypothesis. Because men generally exhibit uniform preference for neotenous women's faces, Elia (2013) questioned if women's varying preferences for neotenous men's faces could "help determine" the range of facial neoteny in humans. Trying to rescue Louis Bolk's theory, Stephen Jay Gould objected to the ranking of races as more or less neotenous, but Gould argued that if one used the terms set forth by 1920s proponents of racial neoteny, "Asians" are "clearly" the most neotenized human "race". Ashley Montagu said that the "Mongoloid skull generally, whether Chinese or Japanese, has been rather more neotenized than the