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.
Biological anthropology trait. However, scientific racism still persisted in biological anthropology, with prominent figures such as Earnest Hooton and Aleš Hrdlička promoting theories of racial superiority and a European origin of modern humans. In 1951 Sherwood Washburn, a former student of Hooton, introduced a "new physical anthropology." He changed the focus from racial typology to concentrate upon the study of human evolution, moving away from classification towards evolutionary process. Anthropology expanded to include paleoanthropology and primatology. The 20th century also saw the modern synthesis in biology: the reconciling of Charles Darwin’s theory of evolution and Gregor Mendel’s research on heredity. Advances in