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.
Canadian Association for Physical Anthropology mission statement of CAPA/ACAP, as listed on the website, is as follows: "The Canadian Association of Physical Anthropology / L'Association Canadienne D'Anthropologie Physique is a learned society of international scholars and students whose aim is to promote and increase awareness and understanding of physical (biological) anthropology among its membership, as well as to supporting institutions and agencies and the public at large. Physical anthropologists study adaptation, variability and evolution in a biocultural context. Our members recognize and celebrate the geographic and temporal diversity and complexity of ancient and modern humankind, our hominid forebears and our nonhuman primate cousins and their