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Theory Of Evolution Essay, Research Paper

Theory of Evolution What is Evolution? Evolution is the process by which all living thingshave developed from primitive organisms through changes occurring overbillions of years, a process that includes all animals and plants. Exactly howevolution occurs is still a matter of debate, but there are many differenttheories and that it occurs is a scientific fact. Biologists agree that all livingthings come through a long history of changes shaped by physical andchemical processes that are still taking place. It is possible that all organismscan be traced back to the origin of Life from one celled organims. The most direct proof of evolution is the science of Paleontology, orthe study of life in the past through fossil remains or impressions, usually inrock. Changes occur in living organisms that serve to increase theiradaptability, for survival and reproduction, in changing environments.Evolution apparently has no built-in direction purpose. A given kind oforganism may evolve only when it occurs in a variety of forms differing inhereditary traits, that are passed from parent to offspring. By chance, somevarieties prove to be ill adapted to their current environment and thusdisappear, whereas others prove to be adaptive, and their numbers increase.The elimination of the unfit, or the “survival of the fittest,” is known asNatural Selection because it is nature that discards or favors aarticular being. Evolution takes place only when natural selectionoperates on apopulation of organisms containing diverse inheritable forms. HISTORY Pierre Louis Moreau de Maupertuis (1698-1759) was the firsttopropose a general theory of evolution. He said that hereditary material,consisting of particles, was transmitted from parents to offspring. Hisopinionof the part played by natural selection had little influence on othernaturalists. Until the mid-19th century, naturalists believed that eachspecies wascreated separately, either through a supreme being or throughspontaneousgeneration the concept that organisms arose fully developed from soil orwater. Thework of the Swedish naturalist Carolus Linnaeus in advancing theclassifying ofbiological organisms focused attention on the close similarity betweencertainspecies. Speculation began as to the existence of a sort of bloodrelationshipbetween these species. These questions coupled with the emergingsciences ofgeology and paleontology gave rise to hypotheses that the life-forms ofthe dayevolved from earlier forms through a process of change. Extremelyimportant wasthe realization that different layers of rock represented different timeperiods andthat each layer had a distinctive set of fossils of life-forms that hadlived in the past. Lamarckism Jean Baptiste Lamarck was one of several theorists whoproposed anevolutionary theory based on the “use and disuse” of organs. Lamarckstated thatan individual acquires traits during its lifetime and that such traitsare in some wayput into the hereditary material and passed to the next generation. Thiswas an attempt to explain how a species could change gradually overtime.According to Lamarck, giraffes, for example, have long necks because formanygenerations individual giraffes stretched to reach the uppermost leavesof trees, ineach generation the giraffes added some length to their necks, and theypassed thison to their offspring. New organs arise from new needs and develop in the extent that they are used, disuse of organs leads totheir disappearance. Later, the science of Genetics disprovedLamarck’s theory, itwas found that acquired traits cannot be inherited. Malthus Thomas Robert Malthus, an English clergyman, through hiswork An Essayon the Principle of Population, had a great influence in directingnaturalists towarda theory of natural selection. Malthus proposed that environmentalfactors such asfamine and disease limited population growth. Darwin After more than 20 years of observation and experiment,Charles Darwinproposed his theory of evolution through natural selection to theLinnaean Societyof London in 1858. He presented his discovery along with another Englishnaturalist, Alfred Russel Wallace, who independently discovered naturalselection atabout the same time. The following year Darwin published his fulltheory,supported with enormous evidence, in On the Origin of Species. Genetics The contribution of genetics to the understanding ofevolution hasbeen the explanation of the inheritance in individuals of the samespecies. GregorMendel discovered the basic principles of inheritance in 1865, but hiswork wasunknown to Darwin. Mendel’s work was “rediscovered” by other scientistsaround1900. From that time to 1925 the science of genetics developed rapidly,and manyof Darwin’s ideas about the inheritance of variations were found to beincorrect.Only since 1925 has natural selection again been recognized as essentialin evolution. The modern theory of evolution combines the findings ofmoderngenetics with the basic framework supplied by Darwin and Wallace,creating thebasic principle of Population Genetics. Modern population genetics wasdevelopedlargely during the 1930s and ’40s by the mathematicians J. B. S. Haldaneand R. A.Fisher and by the biologists Theodosius Dobzhansky , Julian Huxley,Ernst Mayr ,George Gaylord SIMPSON, Sewall Wright, Berhard Rensch, and G. LedyardStebbins. According to the theory, variability among individuals in apopulation ofsexually reproducing organisms is produced by mutation and geneticrecombination. The resulting genetic variability is subject to naturalselection in theenvironment. POPULATION GENETICS The word population is used in a special sense to describeevolution. Thestudy of single individuals provides few clues as to the possibleoutcomes ofevolution because single individuals cannot evolve in their lifetime. Anindividualrepresents a store of genes that participates in evolution only whenthose genes arepassed on to further

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