Human Evolution, Climate, Diet, and Migration
what respects do the old large-scale dread diseases, like
small pox, cholera, plague, and typhoid differ from large-scale
diseases of today, like heart disease, diabetes, depression
is the result of the 2 million year history of the hominid species. The
hominid species is a family of the “superfamily” of apes and
contains orangutans, African apes, and humans. The superfamily of apes
is of the larger order called primates. The hominid family has two subfamilies:
(1) ponginae, consisting of orangutans and gibbons, and (2) Homininae,
consisting of the African apes (gorillas and chimpanzees) and humans.
The relationship between the members of the hominid family is close. Enzymes
and other proteins of man and chimpanzee are identical.
million years ago, the hominid species split off from the chimpanzees.
Two million years ago, there were several vegetarian and meat-eating hominid
species in Africa. For the last 30,000 or so years, the only remaining
hominid species is the Homo sapiens, which originally emerged around 80,000
years ago in Africa and then slowly spread world wide. See http://www.becominghuman.org
for more information about human evolution.
1: The major dispersal routes by the modern human species
Homo sapiens during the past (approximately) 75,000 years. The sea
level was 100-140 metres lower during the most recent (Wurm) glaciation,
which extended from around 85,000 to 15,000 years ago. Dispersal
dates are only approximate, and derive from studies of fossil humans
and stone tools. The dates shown here are averaged from several
sources. (Image and caption from Human Frontiers, Environments,
and Disease: Past Patterns, Uncertain Futures, by Tony McMichael;
Cambridge University Press, 2001.)
most fundamental level, we can think of health as proper biological functioning.
An important aspect of health often not recognized in the technological
paradigm is that good health or "normal" health is a product
of evolutionary biology. The natural environment in which we evolved over
millennia has provided for each of us a set of conditions requisite or
at least most desirable for our well-being. These environmental factors
have predisposed our physiology to function best under certain types of
conditions, such as climate and food. Even our genetics which determine
some of these predispositions and susceptibilities have been subject to
natural selection over hundreds of thousands of years. For example, people
in sunny and hot climates have developed darker skins because of an abundance
of melanin in their skins, giving it a darker coloring. Melanin is a pigment
that helps absorb sunlight without burning the skin, and particularly
the ultraviolet from causing skin cancer. Thus the dark pigmentation of
people living in equatorial regions has a positive effect. This pigmentation
also plays a role in moderating the necessary absorption of ultraviolet
by our skin. Ultraviolet radiation converts 7-dehydrocholestorol, a compound
made by the liver and brought near the skin through the blood, into Vitamin
D. Vitamin D is necessary for healthy bones as it helps the absorption
of calcium produced in the intestines during digestion. So pigmentation,
like many other features of nature, has a dual function.
happens when people move from equatorial regions to higher latitudes?
Dark-skinned immigrant children living at high latitudes and in dark urban
areas develop Vitamin D deficiency. Prehistoric bones recovered from Norway
and Denmark show evidence of a large rate of rickets. Thus early populations
show deviations from good health resulting from the migration. As time
goes on, the people with less susceptibility to that disease survive and
reproduce. Thus natural selection eventually restores the population to
a smaller equilibrium rate of that defect or with only the non-susceptible
surviving, with very little of the defect in the populations. Certain
diseases—especially the auto-immune diseases—therefore show
a difference in rates depending on latitudes, reflecting the fact that
humans originally evolved in the equatorial region. Auto-immune diseases
are those caused when the body reacts to suppress its own immune system.
Examples are child-onset (Type 1) diabetes, rheumatoid arthritis, and