Melanism
is the development of the dark-colored pigment melanin in the skin and is
considered the opposite of albinism. This normally occurs after sunburn or
during pregnancy. Melanin is the primary determinant of the degree of skin
pigmentation, protects the body from harmful ultraviolet radiation, and helps
our eye function properly (hence why albinos who do not have melanin have
eyesight problems).
Melanism is adaptive. Normally
melanism makes species less conspicuous to predators, while others, such as
black panthers, use it to say less conspicuous to prey while hunting during the
nighttime. Adaptive melanism can also lead to the creation of morphs, one of
the most commonly known examples being the peppered moth.
Industrial melanism is the effect
of pollution on different species. When a species is exposed to an environment
polluted by dark soot from industrial pollution, the individuals with darker
pigmentation are favored by natural selection. One of the most common examples
of this is the peppered moth. To camouflage with trees the moths were
originally very light colored but as pollution occurred the lichen on the trees
began to die, exposing the dark bark of the trees. This made the light colored
moths more vulnerable and slowly altered the population as the dark colored
moths were able to survive and reproduce easier than the light colored moths.
One
interesting question that comes to mind is how albino people exist but
melanistic people do not seem to exist. Technically melanistic people do exist,
as melanistic people just have unusually high amounts of melanin. For example,
Addison's disease is characterized by a bronze discoloration of the skin due to
the inadequate secretion of melanin by the adrenal cortex. Another example is melasma, a discoloration of the skin normally
experienced by pregnant women. However, some may wonder why some people are not
born with very dark skin. The difference between albinism and melanism is that
there are a lot of possible inhibitors for gene production of melanism while
there are far fewer ways for genes to produce excessively large amounts of
melanin. There are lots of ways for the melanin gene to not be activated,
however there are fewer ways for the melanin gene to be activated to
overproduce melanin.
PoS
Industrial melanism is the effect
of pollution on different species. When a species is exposed to an environment
polluted by dark soot from industrial pollution, the individuals with darker
pigmentation are favored by natural selection. One of the most common examples
of this is the peppered moth. To camouflage with trees the moths were
originally very light colored but as pollution occurred the lichen on the trees
began to die, exposing the dark bark of the trees. This made the light colored
moths more vulnerable and slowly altered the population as the dark colored
moths were able to survive and reproduce easier than the light colored moths. 
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