Dr. Levy talks about cold adaption in ancient and modern populations. She explains the three-part system that helps keep us warm: cultural adaptions, short-term changes in the body, and evolutionary changes to the body's structures. Along the way, we discuss Bergmann's Rule and Allen's Rule. Both help to explain why groups living in certain climates have the proportions they do. Dr. Levy also shares her innovative methodology to help measure brown fat deposits that aid in non-shivering thermogenesis.