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Divergent Evolution

Divergent evolution occurs when a group from a specific population develops into a new species. In order to adapt to various environmental conditions, the two groups develop into distinct species due to differences in the demands driven by the environmental circumstances. A good example of how divergent evolution occurs is in comparing how a human foot evolved to be very different from a monkey's foot, despite their common primate ancestry. It is speculated that a new species (humans) developed because there was no longer was a need for swinging from trees. Upright walking on the ground required alterations in the foot for better speed and balance. These differing traits soon became characteristics that evolved to permit movement on the ground. Although humans and monkeys are genetically similar, their natural habitat required different physical traits to evolve for survival.

If different selective pressures are placed on a particular organism, a wide variety of adaptive traits may result. If only one structure on the organism is considered, these changes can either add to the original function of the structure, or they can change it completely. Divergent evolution leads to speciation, or the development of a new species. Divergence can occur when looking at any group of related organisms. The differences are produced from the different selective pressures. Any genus of plants or animals can show divergent evolution. An example can involve the diversity of floral types in the orchids. The greater the number of differences present, the greater the divergence. Scientists speculate the greater that two similar species diverge indicates a longer length of time that the divergence originally took place.

There are many examples of divergent evolution in nature. If a freely-interbreeding population on an island is separated by a barrier, such as the presence of a new river, then over time, the organisms may start to diverge. If the opposite ends of the island have different pressures acting upon it, this may result in divergent evolution. Or, if a certain group of birds in a population of other bird of the same species varies from their migratory track due to abnormal wind fluctuations, they may end up in new environment. If the food source is such that only birds of the population with a variant beak are able to feed, then this trait will evolve by virtue of its selective survival advantage. The same species in the original geographical location and having the original food source do not require this beak trait and will, therefore, evolve differently.

Divergent evolution has also occurred in the red fox and the kit fox. While the kit fox lives in the desert where its coat helps disguise it from its predators, the red fox lives in forests, where the red coat blends into its surroundings. In the desert, the heat makes it difficult for animals to eliminate body heat. The ears of the kit fox have evolved to have greater surface area so that it can more efficiently remove excess body heat. Their different evolutionary fates are determined primarily on the different environmental conditions and adaptation requirements, not on genetic differences. If they were in the same environment, it is likely that they would evolve similarly. Divergent evolution is confirmed by DNA analysis where the species that diverged can be shown to be genetically similar.

Resources

Books

Merrell, David J. The Adaptive Seascape: The Mechanism of Evolution. Minneapolis: University of Minnesota Press, 1994.

Gould, Stephen Jay. The Structure of Evolutionary Theory. Cambridge, MA: Harvard University Press, 2002.

Ridley, Mark. Evolution. Cambridge, MA: Blackwell Scientific Publications, 1993.

Other

University of California at Berkeley. "Welcome to the Evolution Wing." UCMP exhibit halls. November 15, 2002 [cited January 13, 2003]. <http://www.ucmp.berkeley.edu/history/evolution.html>.

BioWeb. "Divergent and Convergent Evolution." Earlham. [cited January 14, 2003]. <http://bioweb.cs.earlham.edu/9-12/evolution/HTML/converge.html>.


Bryan Cobb

Additional topics

Science EncyclopediaScience & Philosophy: Evolution to Ferrocyanide