Essay代写范文-自然选择与证据

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Essay代写

　　Natural Selection and A Piece of Evidence

　　Darwin’s theory of natural selection believes that the natural environment is the selector,the individual organism is the object of choice.The natural selection process is the process by which the natural environment preserves the organisms that are suitable for the environment and the organisms that are not suitable for the environment are eliminated.Through natural selection,the small favorable mutations of organisms are accumulated in each generation.Through natural selection,the direction of biological evolution is determined and biological evolution is realized.

　　Entering the 1930s,genetics made great progress on the basis of the basic laws of genetics established by Mendel,and the development of genetics laid the foundation for humans to further explore biological evolution.Modern Darwinism has been created based on the development of genetics and population genetics.Modern Darwinism believes that the unit of biological evolution is not an individual but a group.Through mutation,selection,and isolation,new biological species can be formed and biological evolution can be realized(Lenski,2017).Because mutations can provide raw materials for biological evolution,adaptive mutations can be retained by selection(natural selection),and adaptive mutations can be consolidated and expanded through isolation,leading to a targeted change in the frequency of genes in a population.

　　Natural selection is a very common phenomenon in the natural world.Whether it is a sophisticated or a simple organism,both the past and the living organism must accept the choice of the natural environment.Due to the complexity of natural selection,it is difficult for humans to give comprehensive and profound explanations in a short period of time.The object of natural selection is the phenotypic trait of the organism.Through the role of phenotypic traits,changes in the frequency of alleles in the population can be caused.Therefore,to understand natural selection,people must not only observe the phenotypic traits of organisms,but also statistically analyze the frequency changes of the corresponding alleles in the population.The phenotypic traits of organisms are controlled by the genetic basis,usually between the higher and lower generations,with little difference.

　　The process of biological evolution is extremely slow.It has been difficult to observe for decades of human life.It is obviously impossible for natural selection and biological evolution to be completely visible in a short period of time.It is only possible with the development of science and the improvement of human understanding.In the article by Richard E.Lenski,microorganisms are proposed as the perfect subject of study.Since microorganisms have shorter generations and larger populations than other living species,it makes them an effective way to perform experimental evolution(Lenski,2017).This solves the biggest problem with the theory of natural selection and evolution,which is the lack of evidence.

　　Lenski has presented the results of a long-term evolution experiment(LTEE)in the paper.In a relatively short period of time,biologists were able to create 66,000 generations of E.coli.From the observation on the dynamics of adaptations,it has been found that rate of genetic improvement that brings positive responses to environment change slows down within the first 2,000 generations.The diminishing rate suggests a stabilizing characteristic of natural selection.After around 50,000 generations,the E.coli.population increased in fitness by 70%compared to their first-generation ancestor(Lenski,2017).Meanwhile,a high degree of variety is observed amount the populations of the same generations,which reaffirms the explanation provided by the natural selection theory on the issue of biodiversity.

　　It turns out that adaptation and natural selection is a mixture of gradual and abrupt changes,as one E.coli.Population developed the ability to live on citrate,which is a highly unfavorable environment for their ancestor.A parallelism between phenotypic and genomic features is also observed,with the help of genome sequencing on some generations of the E.coli.“With over 50%of nonsynonymous mutations that arose in nonhypermutable lineages concentrated in just 2%of the protein-coding genes(Lenski,2017),”it indicates that there almost are designated genes responsible for mutation and responding to the changing environment.Despite the parallelism,there has been very few cases of mutations that are identical to each other.This suggests that while the location of mutation is highly concentrated and predictable,the point mutations themselves are extremely enriched and varied.

　　To support and complement the LTEE results,Lenski has made reference to several significant experiments in the field of microorganism studies.The key features of the natural selection and evolution theory has been addressed in the paper with evidence provided.It has shown the stabilizing nature of mutations in response to the environment.The LTEE has also proofed the genetic origin of biodiversity,which lies in concentrated areas in the genes.However,the mutations themselves are highly unpredictable,with the possible of both gradual and abrupt changes.Overall,microorganism studies have been an important tool for the verification and further development of modern Darwinism.