Final answer:
The number of melanocytes is highly variable irrespective of where people live. Skin color shifts gradually with location, creating a spectrum of change. Hair color is determined by the type and amount of melanin produced.
Step-by-step explanation:
The number of melanocytes, which are responsible for skin color, is highly variable irrespective of where people live. It is higher in warmer climates near the equator and lower in colder climates of the northern hemisphere. Skin color shifts gradually with location, creating a gradual spectrum of change rather than distinct boundaries between groups.
Factors such as exposure to ultraviolet radiation and the need for Vitamin D absorption have influenced the evolution of skin pigmentation. Darker skin protects against UV ray damage and folic acid breakdown, while lighter skin allows for greater exposure to ultraviolet radiation and Vitamin D synthesis.
Similar to skin color, hair color is also determined by the type and amount of melanin produced by melanocytes. As people age, melanin production decreases, leading to gray and white hair.