Organism Physiology Evolution of Organisms for Millions Essay

Excerpt from Essay :

Organism Physiology

Evolution of Organisms

For millions of years earth has gone under tremendous changes. This rapid change in environment, landscape and temperature alters the intact system and for surviving this change, a steady modification in living organisms occurs for adaption to surrounding environment. This change is never over night nor does it occur suddenly in newborns, it takes generations to evolve a new feature or characteristic. This adaption is not only in mammals but can also occur in plants and microscopic organisms; plants developed the process of photosynthesis in order to survive in oxygen abundant environment and micro-organisms being not used to access of oxygen either went extinct or formed symbiotic association with oxygen for survival.

The rule of survival of the fittest as determined by nature also applies to all living beings inhabiting earth. A simple example would be a breed of heavy coated sheep living in extreme hot conditions can either migrate to higher lands or be susceptible to resulting diseases that can wipe out an entire colony. Overtime this change can result in to newborns having a thinner coat for survival but such a change occurs over considerable time.

The most quoted example of a living thing adapting to changing environment is giraffe and through transformation of horse like neck into a long neck for survival.

An evolutionary theorist Jean-Baptist Lamarck described giraffe's evolution as a habit of reaching for tall trees to get fresher food (leaves) that resulted in longer forelegs then hind legs as consistently reaching for leaves high in the trees exerted more pressure on hind legs and kept forelegs hanging which resulted in longer forelegs. Similarly keeping its neck stretched upwards in order to have the freshest leaves high up in the trees evolved its neck to a point where a standing giraffe can be measured up to six meters or more. Another reason for giraffe's reaching up for food was the lower vegetation eaten by other animals. Lamarck also suggested that in the time drought when vegetation lacked in dry regions giraffe's had the advantage of being the only four legged mammal that can reach up to trees (Gould, 2002).

Charles Darwin in his book origin of species also supports the view point of Lamarck and further explains that such a change is generated through inheritance and that the most suited feature with respect to nature and effects of more used parts in a body would prevail in coming generations. Darwin also suggests that original group having variety of neck lengths existed but since natural selection favored longer necks for feeding purpose the favored characteristic prevailed in the coming generation and hence after many generations the neck length of the whole group has increased at an average but variation still exists (Darwin, 1872). See figure 1.

A different descriptive attempts made by Pincher (1949), was related to giving more importance to giraffe's forelegs then its long neck; i.e. The long legs give giraffe a longer stride hence increased speed which only makes it vulnerable to loins as hunters. The evolution of long legs could have come as a natural selection resulting in a heavier leaner…

Sources Used in Document:


Darwin, C.R. 1872. The origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. 6th ed. London: John Murray.

Gould, S.J. (2002). The Structure of Evolutionary Theory. Cambridge, MA: Belknap Press.

Pincher, C. (1949). "Evolution of the Giraffe," Nature, 164, pp. 29-30.

Simmons, R. & Scheepers, L. (1996). "Winning by a Neck: Sexual Selection in the Evolution of the Giraffe," The American Naturalist, 148, pp. 771-786.

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