Thermoregulation in mice, rats and humans: An insight into the evolution of human hairlessness

The thermoregulation system in animals removes body heat in hot temperatures and retains body heat in cold temperatures. The better the animal removes heat, the worse the animal retains heat and visa versa. It is the balance between these two conflicting goals that determines the mammal's size, heart rate and amount of hair. The rat's loss of tail hair and human's loss of its body hair are responses to these conflicting thermoregulation needs as these animals evolved to larger size over time.