Human populations in low-UV environments tend to have more lightly pigmented skin. One explanation is that the selective pressur
e for dark skin decreases as UV intensity decreases. At the same time there is selection for lighter skin to absorb more UV radiation, which is needed for vitamin D production. What evidence supports the vitamin D hypothesis for the evolution of lighter skin tones? a. lightly pigmented people tend to be at higher risk of vitamin D deficiency b. red hair and light skin are typical of people of northern European descent c. lightly pigmented people cannot synthesize vitamin D in high-UV environments, such as equatorial Africa d. indigenous peoples living at high latitudes have darker skin, but they eat foods rich in vitamin D
The evidence that supports the vitamin D hypothesis for the evolution of lighter skin tones is indigenous peoples living at high latitudes have darker skin, but they eat foods rich in vitamin D.
This shows that consuming food rich in Vitamin D is not the only factor that determine the skin color as indigenous people live in high latitude areas and consume food rich in vitamin D and still have darker skin.
The muscular and nervous systems enable the involuntary breathing mechanism. The main muscles in inhalation and exhalation are the diaphragm and the intercostals (shown in blue), as well as other muscles. Exhalation is a passive action, as the lungs recoil and shrink when the muscles relax.
