One Mammalian characteristic is that the body is covered by hair or fur. Humans have hair which serves many purposes. The hair on the head keeps us warm. The body loses a great deal of heat through the head and hair helps to regulate the temperature of the body by providing insulation on cold days. When it is hot, if your head becomes sweaty, as it evaporates, this removes heat from the body causing a cooling effect. Eyelashes and eyebrows help prevent dust from entering the eyes. On hot days, muscles in the skin make hair lie flat which helps to release heat. On cold days, erector muscles cause goosebumps on the skin and hairs on the skin stand up which helps to insulate the body and keep it warm. Perhaps hair can be attractive to the opposite sex. Hairs can sense air currents and movement due to the fact that they are connected to nerve endings. Hair also protects parts of the body.