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.
Ecological anthropology to study a wide range of human responses to environmental problems. In the 1960s, ecological anthropology first appeared as a response to cultural ecology, a sub-field of anthropology led by Julian Steward. Steward focused on studying different modes of subsistence as methods of energy transfer and then analyzed how they determine other aspects of culture. Culture became the unit of analysis. The first ecological anthropologists explored the idea that humans as ecological populations should be the unit of analysis, and culture became the means by which that population alters and adapts to the environment. It was characterised by systems theory,