Running head: GEOGRAPHICAL ORIGIN & PHYSICAL VARIATIONS IN HUMANS
Does Geographical Origin Account for the Physical Variations in Modern Humans?
Victoria A. Malone
Salt Lake Community College
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GEOGRAPHICAL ORIGIN & PHYSICAL VARIATIONS IN HUMANS
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Does Geographical Origin Account for the Physical Variations in Modern Humans?
The Origin of Modern Humans
Humans, apes and monkeys are all members of the Primate order, sharing many traits,
characteristics and common ancestors. The earliest primates evolved about 65 million years ago
in the epoch referred to as the Paleocene Epoch. Fossil evidence indicates that they were smallbrained arboreal fruit eaters, comparable to modern tree shrews today. Primates of the Eocene
epoch, which was 56 to 33 million years ago (mya) were similar and ancestral to contemporary
lemurs, and tree shrews, and are classified as early primates. The branching of Old World
monkeys and hominoids occurred around 33-23 mya, as the Oligocene Epoch was ending and
the Miocene Epoch was just beginning (23-5 mya). Speciation followed when the apes and
hominoids diverged from their fellow primate Infraorder members; the Old World and New
World monkeys, who both belong to the Taxonomic Family. Speciation continued, separating the
Asian great apes (the orangutan being the only surviving descendant) from the African
hominoids (of which modern humans are descendant from), about 15 to 10 million years ago.
Genetic evidence suggests that the ancestral lines of gorillas diverged about 8 million years ago
and that chimpanzees and hominids diverged about 5 million years ago (fig. 1a)
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(Figure 1a) Figure
Dispersal of Modern Humans
By the time Homo erectus was discovered, a major expansion into new environments was
already under way. Populations of Homo erectus were not only living in Africa (where believed
to have primarily originated), but fossils were also found in Southeast Asia, Europe and China.
Just as the differentiation of animal life through the Pleistocene differed from one region to
another and coupled with different selective pressures, were geographical features, which
restricted or prevented gene flow between populations of different faunal regions.
To explain the dispersal of Modern Humans, there are two main hypotheses, but
according to the various replacement models, suggest that Modern Humans originated in Africa
and migrated to other parts of the world, and interbred with pre-modern human groups, so as not
completely replace the existing pre-modern human populations indigenous to the area, (this
emphasizes the partial replacement theory).
Human Variations.
The many different variations of modern humans or Homo sapiens today are variations
are known as races. Different races come from different parts of the world, the differences
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between races are largely due to the environmental factors of the region that our ancestor Homo
erectus Skin color for example can mainly be attributed to the amount of sunlight his or her
ancestors were exposed to millions of years ago creating allele frequencies visible in DNA.
Many behavioral traits are learned or acquired by living in a society; other characteristics,
such as blue eyes, are passed on physically by heredity. Environment affects both. The physical
characteristics of both populations, and individuals are a product of the interaction between
genes and environments.
A species faced with changing environmental conditions has within its gene pool the
possibility of producing individuals with traits appropriate to its altered life. Many may not
achieve reproductive success, but those whose physical characteristics enable them to do well in
the new environment will usually reproduce, so that their genes will become more common in
subsequent generations. Thus, humankind has been able to survive and thrive in a variety of
environments.
Physical Characteristics & Geographical Locations.
Modern human’s genes have a predisposition to a particular skin color, but the skin color
one actually has is strongly affected by environmental factors such as the amount of solar
radiation. Genetic variants will be expressed in different frequencies in these geographically
dispersed populations. In the Old World, populations of Homo sapiens living in the tropics have
a higher frequency of genes for dark skin than do those living in more northerly regions.
For most characteristics, they are within the gene pool of Homo sapiens variant forms of
genes, known as alleles. In the color of an eye, shape of a nose, the texture of skin, many
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variations can occur. This kind of variability, found in many animal species, signifies a rich
potential for new combinations of characteristics in future generations.
The Meaning of Race.
Early anthropologists tried to explore the nature of human species by systematically
classifying H. sapiens into subspecies or races, based on geographic location and physical
features such as skin color, body size, head shape and hair texture. Such classifications were
continually challenged by the presence of individuals who did not fit the categories.
The fact is, generalized references to human types such as "Asiatic" or "Mongoloid", "European"
or "Caucasoid", and "African" or "Negroid" were at best mere statistical abstractions about
populations in which certain physical features appeared in higher frequencies than in other
populations.
Race as a Biological concept.
To understand why the racial approach to human variation has been so unproductive, we
must first understand the race concept in strictly biological terms.
In biology, a race is defined as a population of a species that differs in the frequency of different
variants of some gene or genes from other populations of the same species. Three important
things to note about this definition:
Physical Variables.
Not only have attempts to classify people into races proven counterproductive, it has also
become apparent that the amount of genetic variation in humans is relatively low, compared to
that of other primate species. Nonetheless, biological variation is a fact of life. Physical
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anthropologists have learned a great deal about variation, much of it is related to climatic
adaptation. A correlation has been noted between body build and climate:
Generally, people native to regions with cold climates tend to have greater body bulk (not to be
equated with fat) relative to their extremities (arms and legs) than do people native to regions
with hot climates, who tend to be long and slender. Interestingly, these differences show up as
early as the time of Homo erectus.
Certain body builds are better suited to particular living conditions than others: People with
larger body bulk and shorter extremities may suffer more from summer heat than someone
whose extremities are long and whose body is slender. But they will conserve needed body heat
under cold conditions. The reason is that a bulky body tends to conserve more heat than a less
bulky one, since it has less surface relative to volume. People living in hot, open country, by
contrast, benefit from a body build that can get rid of excess heat quickly so as to keep from
overheating; for this, long extremities and a slender body, which increase surface area relative to
volume, are advantageous.
Anthropologists have also studied such body features as nose, eye shape, hair texture and
skin color in relation to climate. Skin color in modern humans exhibit tremendous variations.
This is a function of four factors: transparency or thickness of the skin, distribution of blood
vessels, and amount of carotene and melanin in a given area of skin. Exposure to sunlight
increases the amount of melanin, darkening the skin. Natural selection has favored heavily
pigmented skin as protection against the strong solar radiation of equatorial latitudes. In northern
latitudes, natural selection has favored relatively de-pigmented skins, which can utilize relatively
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weak solar radiation in the production of Vitamin D. Selective mating, as well as geographical
location, plays a part in skin color distribution.
Human Biological Evolution
In the course of their evolution, humans in all parts of the world came to rely on cultural
rather than biological adaptation for their survival. Nevertheless, as they spread beyond their
tropical homeland into other parts of the world, they did develop considerable physical variation
from one population to another. Human genetic variation generally is distributed in such a
continuous range, with varying clusters of frequency. For example our hair is curly or straight,
our skin is lightly to heavily pigmented, and in height we range from short to tall. The
significance we give our variations and the way we perceive them is strongly determined by our
culture.
Variations of the Future
Although many of our physical variations are still apparent in human populations today, the
increasing effectiveness of cultural adaptation has reduced its importance. Cultural practices
today are affecting the human organism in important, often surprising, ways.
The probability of alterations in human biological makeup induced by culture raises a number of
important questions. By trying to eliminate genetic variants, are we weakening the gene pool by
allowing people with hereditary diseases and defects to reproduce? Are we reducing chances for
genetic variation by trying to control population size? We are not sure of the answers to these
questions.
GEOGRAPHICAL ORIGIN & PHYSICAL VARIATIONS IN HUMANS
References
http://vicinvictopia.weebly.com/
Jurmain, R., Kilgorer, L., & Trevathan, W. (2013). Human origins, evolution and diversity. (9th
ed.). Mason: Cengage Learning.
Platter, B. (n.d.). Retrieved from http://www.lurj.org/article.php/vol4n1/genome.xml
Kramer/Pearson, A. (n.d.). The Natural History and Evolutionary Fate of Homo erectus.
Retrieved from www.pearsonhighered.com/assets/hip/us/hip_us.../0205158803.pdf
Modern Human Variation: Models of Classification. (n.d.). Retrieved from
http://anthro.palomar.edu/vary/vary_2.htm
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