Dispersion of Humans

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Biology 103

2005 Second Paper

On Serendip

Dispersion of Humans

Iris Mejia

Segregation has been, and can be, seen occurring wherever from lunch tables to areas in cities. Understanding why this occurs is highly complicated due to the many factors that lead to people living in the midst of others like themselves. Among these factors are externalities that have caused certain people to be found in a given area. This reasoning can account for what looks like global segregation. It is obvious that people in a given geographic area have a set of characteristics that differentiates them from other parts of the world. What factors have caused these differences? In order, to understand the factors that may have influenced human variation a look at Homo sapien evolution is the first step.

The origin of the modern humans is a topic that has been looked at by scientist in many fields, such as molecular biologists and anthropologists. These scientists have come up with differing time lines on human evolution. Molecular biologists believe that "modern humans evolved in Africa about 200,000 years ago, from where they migrated throughout the rest of the world."(1) On the other hand, Anthropologists believe "modern humans evolved on a broad geographic front, absorbing rather than replacing" (1) primitive humans. Therefore, without any intermediary theories if one group of scientists is right then the second is found in error so intensive research has been done on this matter. In 1987, a conference took place at the University Of Cambridge, England to discuss evolutionary theory. A population geneticist, a demographer and an ecologist all supported the molecular biologists statement. Why does it matter how humans evolved? Because depending on the theory believed, there are implications about human dispersal across the globe.

Let us begin by looking at the molecular biologists' theory. Their statement suggests that humans all came from Africa and replaced other humans as we dispersed across the globe. There is only one point of origin and so extensive migration would have ensued for the present distribution of humans. Evidence of this possibility was seen at Klasies River Mouth where human fossils where found to be between 115,000 and 80,000 years old (1). Assuming this, we all come from the same root and so have similar genes. Then why do we differ so much in characteristics? The factors that can explain this comes from the separation of peoples carrying along certain genes that continued to be passed down along the given lineage. Even though, the same genes were present certain genes were manifested more often and thereby some genes may have been turned off. Natural selection played a major role as well; because some people are unable to survive the changes in their environment as they move across different terrain, therefore, certain genes die along with them. An example of this is melanin, which "play a major role in the quenching of free radicals produced by ultraviolet radiation" (2). It is manifested in the color of our skin. Africans have dark complexions since they are where sun exposure is greatest. This suggests that as populations moved from Africa their bodies adapted to less sun exposure for survival.

Before the evidence at Klasies River Mouth, anthropologists believed that humans
across the globe independently evolved at the same time without interactions with one another. The best fossil records were found throughout the eastern hemisphere of the world, evidence that showed modern humans had many points of origins. Assuming this theory, we cannot talk about dispersal or movement as the reasoning for the striking variation between people in the world. In this case, each group evolved on its own with its own gene pool in given locations so the disparity is best explained by the isolation of these groups for a large number of years.

The theories mentioned give us a good idea as to some of the factors that have
affected human differences in the world. They include humans carrying certain genes and
moving with them in a group, natural selection, genes being turned off or not recurring in a given population, and human isolation.


[1] Lewin, Roger. Africa: Cradle of Modern Humans, Science, New Series, Vol.237, No. 4820.
[2] Cesarini, J.P. M.D. Melanins and their possible roles through biological evolution, Advances in Space Research, Vol. 18, Issue 12, 1996.
Campbell, Neil and Reece, Jane. Biology. Benjamin Cummings San Francisco, CA, 2002.
Pritchard, Jonathan. Genetic Data and the African Origin of Humans, Science, New Series, Vol. 274, No. 5292.

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