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Divergent evolution is the accumulation of differences between groups which can lead to the formation of new species, usually a result of diffusion of the same species to different and isolated environments which blocks the gene flow among the distinct populations allowing differentiated fixation of characteristics through genetic drift and natural selection. Primarily diffusion, the basis of molecular division, can be seen in some higher-level characters of structure and function that are readily observable in organisms. For example, the vertebrate limb is one example of divergent evolution. The limb in many different species has a common origin, but has diverged somewhat in overall structure and function. Alternatively, "divergent evolution" can be applied to molecular biology characteristics. This could apply to a pathway in two or more organisms or cell types, for example. This can apply to genes and proteins, such as nucleotide sequences or protein sequences that derive from two or more homologous genes. Both orthologous genes (resulting from a speciation event) and paralogous genes (resulting from gene duplication within a population) can be said to display divergent evolution. Because of the latter, it is possible for divergent evolution to occur between two genes within a species. In the case of divergent evolution, similarity is due to the common origin, such as divergence from a common ancestral structure or function has not yet completely obscured the underlying similarity. In contrast, convergent evolution arises when there are some sort of ecological or physical drivers toward a similar solution, even though the structure or function has arisen independently, such as different characters converging on a common, similar solution from different points of origin. This includes analogous structures. == Usage == J. T. Gulick (1832-1923) founded the usage of the term "divergent evolution"〔 〕 and of other related terms, which can vary slightly in usage from one researcher to the next. Furthermore, the actual relationships might be more complex than the simple definitions of these terms might imply. "Divergent evolution" most commonly applies when someone invokes evolutionary relationships; whereas "convergent evolution" refers to cases which evolve independently but result in similar structures and functions. Some scholars use the term "parallel evolution" to describe the appearance of a similar structure in closely related species, whereas "convergent evolution" primarily refers to similar structures in much more distantly related clades. For example, some might regard the modification of the vertebrate limb to become a wing in bats and birds as an example of parallel evolution. Vertebrate forelimbs have a common origin and thus, in general, show divergent evolution. However, the modification to the specific structure and function of a wing evolved independently and in parallel within several different vertebrate clades. Divergent evolution has much to do with humans and with the way they function from day to day. In complex structures, cases may occur where some aspects of the structures result from divergence and other aspects have their origins in convergence or in parallelism. In the case of the eye, researchers initially thought that different clades had different origins of the eye, but some now question this interpretation. It is possible that induction of the light-sensing eye during development might have diverged from a common ancestor across many clades, but the details of how the eye is constructed—and in particular of the structures that focus light in cephalopods and vertebrates, for example—might have some convergent or parallel aspects to it, as well. Darwin's finches provide a good example of divergent evolution. They have over 80 varieties which all diverged from one original species of finch.〔 John Barnes〕 For another example of divergent evolution, note the organisms having 5-digit pentadactyle limbs - like humans, bats, and whales. They have evolved from a common ancestor but have become different due to environmental pressures. The divergent evolution of wolves and domesticated dogs from a common ancestor - presumably the grey wolf - provides another example.〔http://www.biomedcentral.com/1741-7007/8/20/〕 Recent studies of the mitochondrial DNA of wolves and of domesticated dogs have found great divergence while also supporting the hypothesis that dogs descend from wolves.〔 http://www.sciencemag.org/content/276/5319/1687.abstract 〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Divergent evolution」の詳細全文を読む スポンサード リンク
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