Throughout time, one theory has remained constant in terms of why giraffes developed longer necks. The idea, which was presented by Charles Darwin states quite simply that giraffes selected for longer necks in order to reach the food that was higher off the ground during the dry season. No one has ever challenged that idea until 1996. Initially, Gould argued that "the story-the giraffe evolved its long neck in competition to reach scare foliage-is supported by no evidence" (18). That's when two scientists, Robert Simmons and Lou Scheepers made the claim that necks evolved for a very different reason: sexual selection. Within this paper, information will be presented that argues both for and against the theories made by Darwin and Simmons and Scheepers.
Giraffes are placed in the family, Giraffidae, separate from other animals such as the camel, deer, and cow. Typically, giraffes are about 19 feet tall and can weigh as much as 4000 pounds. The evolution of modern giraffes began about 1 million years ago from a similar species known as Giraffa jumae. Those species were known for their massive skeletons and antler-like structures, not found on giraffes of today (Simmons 772). Today, there are nine widely excepted subspecies of the giraffes which are differentiated by the spots on the trunks and their geographic region.
In the article, "Winning By a Neck: Sexual Selection in the Evolution of Giraffes," Simmons and Scheepers state their purpose as to evaluate the theory proposed by Darwin as well as present their own. The theory by Darwin known as the Interspecific Feeding Competition has many assumptions that must hold up for it to be true. One assumption is that tall trees must ...
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... This is shown through the way that the animals feed and the disproportionate increase in neck length compared to other components within the giraffe. The evidence presented in this case offers much more support for the idea that sexual selection is responsible. However, much more investigation must take place in order for the theory to be considered acceptable.
Brownlee, A. Evolution of the Giraffe. Nature. Vol. 200:1963.
Gould, Stephen J. The Tallest Tale. Natural History. May 1996.
Kodrick-Brown, A., and J. H. Brown. Truth in Advertising: The
Kinds of Traits Favored by Sexual Selection. The American
Naturalist. Vol. 124:1984. Pp. 309-323.
Simmons, Robert E. Winning By a Neck: Sexual Selection in the
Evolution of Giraffe. The American Naturalist. Vol.
148:1996. Pp. 771-786.
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