Human variation

Topics: Ultraviolet, Human skin color, Human Pages: 5 (1798 words) Published: November 11, 2013

Human Variation

There are many different types of human variation that are influenced by a population’s geographic location, including skin color, height, and body proportions. Many geographic areas are associated with certain physical characteristics that cause them to be commonly classified as different races, which also include hair color, eye color, and cranial shape. These characteristics are in addition to the physical characteristics listed above that are influenced by the geographic location of the population. In examining which characteristics would be beneficial based on the location of the population, and were selected for or against based on those locations, and which characteristics were likely a result of other evolutionary influences such as genetic drift or bottlenecking; we begin to see how genetic variation within the Homo Sapien species is influenced by both geographic environment and the amount of variation present in the gene pool of the population. Many physical characteristics are polygenic and are influenced by genes at two or more loci, and they can be expressed in both dominant and recessive forms. Because of this, populations within a specific geographic location have more variation when compared among themselves than when compared with other members of the human species as a whole (Jurmain, 309). Populations of certain geographic locations express similar physical characteristics are easily identifiable, such as skin color, hair color, eye color, and body proportions, which has caused these populations to be separated into separate “races” over the years. It is not necessarily beneficial to determine why these physical characteristics exist to separate different regional populations from one another into races or sub-categories, but it can be very beneficial in helping to see how the human species has evolved over time and how certain adaptations are made in response to environment. In first examining physical characteristics of populations in certain geographic areas, and whether or not they are selected in response to environment, we look at which characteristics would provide an advantage to an individual living in the surrounding environment. The predominant environmental influence that may influence physical characteristics appears to be proximity to the sun. There are two main effects that proximity to the sun has on the human body, increased or decreased exposure to UV radiation and climate temperatures. The effects of the sun have different influences on human variation depending where the population is located, with populations closer to the equator having more frequent exposure to UV radiation and warmer temperatures, and populations farther from the equator having less frequent exposure to UV radiation and cooler temperatures. In geographic areas with more frequent exposure to UV rays the populations tend to have darker skin coloration than in areas that have less frequent exposure to UV rays. This appears to have happened because all early hominins originated from an area in Africa. As early hominins evolved, at some point they started losing body hair and started developing sweat glands in response to warmer temperatures. They did not yet wear clothing, spent their days outdoors, and did not frequently live in shelters. This meant that they had frequent exposure to the sun and UV rays. Darker skin would have been selected to help protect the body from the harmful effects of the sun by helping to block UV radiation that can cause cancer, as well the depletion of folate serum levels. Folate deficiencies can cause complications during pregnancy that can prevent successful reproduction, like neural tube defects (Jurmain, 318). Because of this, individuals with darker skin in areas with frequent UV radiation would be more suited to natural selection as they would have had more individuals reach reproductive age than individuals with...

Bibliography: Graves Jr., Joseph L. The Emporer’s New Clothes: Biological Theories of Race at the Millennium. New Brunswick: Rutgers University Press, 2001.
Gugliotta, Guy. The Great Human Migration: Why humans left their African homeland 80,000 years ago to colonize the world. July 2008.
Jurmain, Robert, Lynn Kilgore, Wenda Trevathan. Essentials of Physical Anthropology. Eight Edition. Wadsworth Cengage Learning, 2011.
Wolpoff, Milford, Rachel Caspar. Race and Human Evolution. New York: Simon & Schuster, 1997.
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