Evolution of giraffe neck

Solo disponible en BuenasTareas
  • Páginas : 6 (1464 palabras )
  • Descarga(s) : 0
  • Publicado : 14 de febrero de 2011
Leer documento completo
Vista previa del texto
Evolution of Giraffe Neck
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 ongiraffes 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 theoryby 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 have been present on the African savannas back when the selection took place and that competition was initially tough for food. If food was scarce, it makes sense that the giraffes would evolve to keep their species alive. In order for thistheory to remain true, there should be length increases in limbs in the same proportion as to the increases in their heads and necks.

On the other hand, the proposed theory deals with the notion that the length of the giraffe neck increased because the neck is used as a weapon during intrasexual combat (Simmons 773). The basic idea of this is that during competition two males stand next toeach other and exchange hits by using their necks. The top or back of the skull is actually used to knock the competitor to the ground. It is likely that with a larger neck and head, the giraffe is more destructive. It is also assumed that larger and longer necks would be selected for. The process of necking is unique to giraffes and only male giraffes have ever been viewed doing this.Therefore, it is likely that this action is related to sexual selection. Necking has been observed to be very effective for giraffes to obtain their mates. Often the males are knocked unconscious or even killed during the fighting. The violent nature of these fights is unbelievable. Even when an opponent may be knocked to the ground, that does not stop the fight. They may still be kicked or steppedwhich can eventually lead to death.

"Sexual selection is a special form of natural selection that is responsible for the evolution of traits that promote success in competition for mates" (Kodric-Brown 309). There are two different forms of sexual selection: it can be involved with the evolution of traits or it can be related to the evolution of characteristics which would make the male lookmore appealing. Intrasexual competition is involved more with the evolving traits which than can be used as weapons when fighting each other for the right to mate with the female. One general feature of sexually selected traits is that the trait is often more costly for the individual to produce. This holds true for giraffes. Since their necks and heads have disproportionately evolved...
tracking img