Molts that take place during development are also very common. In modern mammals, hair serves to insulate, to conceal, to signal, to protect, and to sense the immediate surroundings. Insulation serves to conserve heat, but also, as in the case of diurnal desert animals such as the camel, to protect against excessive heat. The color of most species is probably cryptic, matching the animal's background. In some cases, such as the dramatic stripes of zebras or tigers, cryptic coloration can only be properly evaluated when the animal is seen against its natural background.
Many mammals are dark dorsally and relatively pale ventrally, a pattern called countercoloration.
Its role is less clear in the case of the many countercolored terrestrial and nocturnal rodents. The pelage also serves to protect the skin from abrasion and from excessive UV radiation. And, through specialized vibrissae, it provides a tactile sense, used, for example, to locate prey or to navigate in total darkness. We do not know when hair evolved, as it is usually not preserved in fossils. Insulation is the most conspicuous and perhaps the most universal function of hair in modern mammals, but hair doesn't serve as effective insulation until it is fairly well developed as pelage.