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1、http:/ 留学生论文专业定制代写网站留学生Essay写作化石是记录进化的证据IntroductionIn general,the termevolutioncan imply a drastic or gradual change from a very broad perspective.Life on earth,the universe,galaxies,as also the earth in general have evolved through millions of years.In this essay we consider only one aspect of evo
2、lution emphasizing on evolution as a biological tool for change among species and consider fossil record as supportive of both evolution theories and also the other theories contrary to evolution.Evolution is the central unifying concept,a theory that successfully connects biology,palaeontology and
3、other branches of science.Evolution is a gradual descent of organisms accompanied by changes that help the organisms to adjust and adapt to the surroundings.Descent with modificationsas Darwin contended implies changes in organisms in successive generations(Mayr,1976).These changes are triggered by
4、the derivation of new species and there is a change in the properties of populations of organisms and these properties tend to transcend the lifetime of any single individual.Newers pecies are modified versions of older species.Although,individual organisms do not biologically evolve,populations evo
5、lve when heritable genetic materials are transmitted from one generation to another.Biological evolution can range from very limited changes to drastic transformations on a large scale changing the entire special together and bringing in new forms.Evolution can thus be defined as inheritable changes
6、 in populations of species that are spread and transmitted over many generations(Zimmer,2002).It is also more scientifically defined as changes in the frequency of alleles within a gene pool carried through different generations as understood in the Darwinian version of the theory(Dawkins,1989).Evol
7、ution studies are supported by detecting changes in gene frequency within a population and the fact that the theory of evolution emphasizes on a common ancestor,only indicates that two or more species show successive heritable changes in populations since they are separated from each other as distin
8、ct forms(Allen and Briggs,1989).Most popular definitions of evolution however highlight not the transmission of heritable traits and changes but the processes of diversity that has given rise to millions of species from the most primitive organisms.Here however we move on to the evidence for and aga
9、inst evolution theories and the role of fossil record in this context.Some researchers claim that the theory of evolution has been supported by four primary sources that serve as evidence(Zimmer,2002;Allenand Briggs,1989):1. The fossil record that tracks changes in early and primitive forms of life2
10、. The anatomical and chemical similarities in the constitutions of different species.3. The genetic changes observed and recorded in several living organisms over several generations4. The geographical spread and distribution of species that seems to suggest a definite pattern,andThe Fossil RecordFo
11、ssils are buried in rock layers as indentations of dead plant and animal materials.The totality of these artefacts and their impressions on the rock formations is considered a fossil record.Fossil record as we have briefly mentioned is the primary source of evidence supporting the theory of evolutio
12、n and the gaps in these records ironically also forms the bone of contention taken up by anti-evolution theorists.Fossil records are used by scientists to understand the process of evolution in general,and the subsequent changes in several species at several times of the earths existence(Donovan and
13、 Paul,1998).The Fossil Record seems to provide an important clue to the changes in primitive and even now extinct species and this definitely helps us to frame a conceptual graph on how evolution has taken shape.Fossil and rock record forms the primary source of evidence collected by scientists for
14、nearly400 years and the consequent database obtained is mainly observational.The fossil record among all other evidence gives a large database of documented changes in past life on earth.The use of Fossil record to study life forms on earth dates back to pre-Darwinian times and the changes in life f
15、orms could be studied from a sequence of layers of sedimentary rocks and fossils of different groups of species were found in each of these successive layers(SA,1982).Sedimentary rocks are found widely across the earths surface and are formed when small particles of sand,mud or gravel,shell or other
16、 materials withered off by water or wind accumulates in sea beds and oceans.As these sediments pileup they bury shells,leaves,bones,and parts of living organisms.Layers of sediments are thus formed for every large period of time and all these layers become subsequently cemented to each other to become different layers of sandstone,limestone,shale and so on.Within these layers of sedimentary rocks the plant and animal remains become buri
