Skin

Mostly naked, potentially sweaty, and variably colored skin is a hallmark of modern human beings. Skin is often overlooked in discussions of human evolution because it is rarely preserved in the fossil record. But because of its central role as an interface between the outside world and the body, it is essential that we study the evolution of skin and, specifically, how our skin differs from that of our ape relatives. We evolved mostly naked skin early in the evolution of the genus Homo for reasons of temperature regulation. Naked skin with lots of sweat glands makes it possible for people to stay cool while they are physically active in hot environments. The loss of hair meant that we lost important protection against the environment, especially strong sunlight. This is when our ancestors evolved permanently dark skin, rich in the natural sunscreen, eumelanin. Eumelanin absorbs much of the harmful ultraviolet radiation that falls on the Earth's surface, and is widely used in nature because of its protective properties and its color. Our ancestors living in equatorial Africa had dark skin and little body hair. This was the universal human condition for a long time for all ancient people living in Africa, including the earliest members of our own species, Homo sapiens. When some people left equatorial Africa and moved to less intensely sunny places, like southern Africa, northern and eastern Asia, and Europe, changes occurred in their skin color. This is because people actually needed to have less eumelanin sunscreen in the skin in order to make it possible for some UV rays to penetrate the skin and make vitamin D. As people moved around early in prehistory, their skin color changed according to the intensity of the sunlight under which they lived. Many aspects of our skin are different from those in apes, and have come to be of great interest and social importance. We pay a lot of attention to skin, we show important emotions through our skin, and we spend a lot of time and effort caring for and decorating our skin. So, it's high time we celebrate its remarkable evolution!