Final answer:
The adaptive coloration of the skin when oxidized by UVR is provided by melanin, a natural pigment that increases following UV exposure as a protective defense mechanism.
Step-by-step explanation:
When oxidized by UVR (ultraviolet radiation), the adaptive coloration of the skin is provided by the pigment known as melanin. During the Neolithic era, humans displayed a variety of skin pigments as an adaptation to different levels of UVR exposure. Melanin plays a crucial role in absorbing UVR, which protects the skin from potential damage. The more melanin present in the skin, the darker the skin tone, and this increased melanin provides a natural defense against the harmful effects of UV exposure including skin cancer. In response to UV-B radiation, which can excite DNA molecules and potentially cause mutations leading to cancer, our bodies increase melanin production through a tanning response as a defense mechanism. This process allows the inert skin layers to absorb future UVR exposure and reduce the risk to living cells below.