Answer 1:
There are many different human skin colors around
the world. Before the mass global migrations of
people during the last 500 years, dark skin color
was mostly concentrated near the equator, living
mostly within 20 degrees of the equator. Lighter
skin pigmented people lived progressively further
away mostly in the northern hemisphere north of 20
latitude.Skin color varies from a very dark brown
to yellow-pink. Researchers know today that skin
color is determined by a complex structure of
multiple genes.
Encoded in the genes are
the pigments responsible for different color
range:Carotene, Hemoglobin, and most importantly
Melanin. Skin color is due mainly to the presence
of melanin which comes in two forms: Pheomelanin
produced by people with light complexioned skin,
and Eumelanin produced by people with dark
colored skin. In lighter skin, color is also
affected by hemoglobin in theblood flowing close
to the skin. Skin color is also affected by the
presencecarotene.More importantly in determining
skin color, people differ in the number and size
of melanin particles in their skin.
The
development of different skin pigmentation in
evolutionary and is part of natures natural
selection. Nature has selected for people with
darker skin in tropical latitudes, where
ultraviolet radiation from the sun is the most
intense. Melanin acts as a protective biological
shield against ultraviolet radiation. Melanin in
the skin helps prevent sunburn and skin damage
that could cause DNA changes and skin cancer. But
melanin must not shield the skin completely. A
certain amount of ultraviolet radiation (UVB) must
penetrate the skin in order for the body to
produce vitamin D, which is very important for our
body. It is needed for the absorption of calcium
for bone growth in order to maintain normal heart
action and a healthy nervous system. Nature
selects for less melanin when ultraviolet
radiation is weak. This is why people who live in
far northern latitudes have lighter skin. Having
dark skin in this environment, is a disadvantage
because it can prevent the body from producing
enough vitamin D. |
