From the first unicellular life on Earth, living things have had the capacity to sense heat and cold and to avoid extreme temperatures. With the development of a bigger brain and a constant body temperature, mammals were able to change their habitats. The interplay between behavior, body temperature, and ambient temperature may have played a crucial role in human evolution. In this book Carl Gisolfi and Francisco Mora tell the evolutionary story of the brain and thermoregulation, with an emphasis on modern humans.