skin pigmentation, which acted as a mech-
anism of natural selection against folate
depletion, and to a lesser extent, DNA dam-
age. The primary factor contributing to the
evolution of dark skin pigmentation was the
breakdown of folate in reaction to ultraviolet
radiation; the relationship between folate
breakdown induced by ultraviolet radiation
and reduced fitness as a failure of normal
embryogenesis and spermatogenesis led to
the selection of dark skin pigmentation. By
the time modern Homo sapiens evolved, all
humans were dark-skinned.
Humans with dark skin pigmentation have
skin naturally rich in melanin (especially eu-
melanin), and have more melanosomes which
provide a superior protection against the del-
eterious effects of ultraviolet radiation. This
helps the body to retain its folate reserves and
protects against damage to the DNA.
D
ark-skinned people
who live in high
latitudes with mild
sunlight are at an
increased risk – espe-
cially in the winter
– of vitamin D defi-
ciency. As a conse-
quence of vitamin D
deficiency, they are at
a higher risk of de-
veloping rickets, and
numerous types of cancers, and possibly car-
diovascular disease and low immune system
activity. However, some recent studies have
questioned if the thresholds indicating Vita-
min D deficiency in light-skinned individuals
are relevant for dark-skinned individuals, as
they found that, on average, dark-skinned in-
dividuals have higher bone density and lower
risk of fractures than lighter-skinned individ-
uals with the same levels of Vitamin D. This is
attributed as, possibly, due to lower presence
of Vitamin D binding agents (and thus higher
72 | Colossium . March 2019
bioavailability) in dark-skinned individuals.
The global distribution of generally dark-
skinned populations is strongly correlated
with the high ultraviolet radiation levels of
the regions inhabited by them. These popula-
tions, almost-exclusively, live near the equa-
tor, in tropical areas with intense sunlight:
Australia, Melanesia, New Guinea, South
Asia and, Africa. Studies into these popula-
tions indicates dark skin is a retention of the
pre-existing high UV adapted state of modern
humans before the out of Africa
migration and not a later evo-
lutionary adaptation. Due
to mass migration and
increased mobility
of people between
geographical
regions in the re-
cent past, dark-
skinned popula-
tions today are
found all over
the world.