The History of the Development of Biological ThoughtThe History of the Development of Biological Thought

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The History of the Development of Biological ThoughtThe History of the Development of Biological Thought

The results of the cladistic analysis are recorded in a cladogram. A cladogram consists of a series of dichotomous branches describing successive divisions of a phyleticline. Two terms in the constituent cladogram are assumed to be completely arbitrary. The first assumes that every existing species is eliminated when a new species appears, and the second assumes that every division is a dichotomous clade. Recognizing that most speciation occurs in isolated, small founder populations, it is clear that such speciation has no effect on the genetics and morphology of parent species. The parent species will remain essentially unchanged for millions of years and new progeny species will be separated from time to time. Strict binary branching is also an unrealistic assumption. When a large taxon reaches a grade-like stage, it may produce several specialized daughter lines, which, although taxonomically sister groups, can develop in their own way and, in addition to similarities derived from the same parent taxon, They have nothing else in common. Some recently constructed cladograms have recognized this,Quercetin Dihydrate Manufacturer, and thus some binary branches have been changed to polytomy (ashlock 1981). For all these reasons, hull (1978) has emphasized that although many cladologists claim that their methods are completely objective and non-arbitrary, they are not based on facts. It is important to keep this in mind in connection with the criticism of cladists of the shortcomings of competing taxonomic approaches. Cladistic classification The difficulties encountered by cladistic analysis are also encountered by traditional taxonomists, but this is not the main reason against cladologists. The main reason is the relationship between cladistic analysis and cladistic classification. As far as a cladologist is concerned,Fungal Chitosan Manufacturer, once the cladistic analysis is over, his task is completed. The reconstructed genealogy represented by the cladogram provides the classification directly. Cladistic classification accurately reflects the branching pattern, and thus the phylogeny of a group can be directly understood. Cladistic classification is the answer if only information on the order of phylogenetic branching points is required to be retrieved from the classification. If more is required, the history of a group reflected in the classification is sought. Species do not entirely ignore the methods of evdutionary divergence and autapomorph characters, that is, the unique features of one of the sister groups. Cladologists disagree with the view that Darwin's genealogy is not itself a classification. Cladologists divide taxa not on the basis of similarity but according to the principle of holography, that is, Glucono Delta Lactone ,Berberine Hydrochloride Factory, all descendants of a common ancestor are United into a single taxon. This leads to an incongruous combination of crocodiles and birds, orangutans and humans as joint taxonomic units. Classification is based entirely on common features, even when, as in the case of birds that evolved from reptiles, the number of unique features greatly exceeds the number of common features. In other words, the cladistic approach ignores that the phylogeny contains two parts: the split of the evolutionary route; and the subsequent evolutionary change of the split branch. The latter part is so important for classification because sister groups tend to have very different evolutionary histories. From two related taxa derived from a most recent common ancestor, one taxa is almost indistinguishable from the ancestral group, while the other may enter a new adaptive zone (adaptive zone) and evolve into an entirely new type. Although they are "sister groups" according to the cladistic nomenclature, taxonomists have traditionally arranged them into different hierarchical levels. There is no better illustration of the difference between cladistics and traditional taxonomy than Henniker's view that sister groups must be arranged at the same level, no matter how different they are from each other in their divergence after separation. For Henniker, cladistic classification is "phylogenetic classification" and seeks to represent phylogenetic evolution in classification (although this method is not suitable for this purpose). But this preoccupation was not shared by some of his followers, who not only opposed the mention of evolution and phylogeny at all, but consciously denied that evolution should be reflected in classification. (michener。 1977;szalay,1977;hull,1979)。 Finally, let me try to make a fair assessment of cladistic classification. The greatest advantage of cladistic analysis is that it is an effective way to test the "naturalness" (that is, monophyletic or monophyletic) of groups that have been previously classified by characterization. Because species and genera can be similar for a variety of reasons, monophyly can only be confirmed by a rigorous analysis of the homology of the characters on which the similarity is based. To understand how fundamental the impact of Henniker's methodology is, one has only to look at recent taxonomic revisions, particularly in relation to fish and certain phyla of insects. Even though some scholars, such as Michener, do not believe that cladogram can be directly translated into classification, they still cautiously try to use the principle of common derivation to divide taxa. Cladistic analysis is particularly effective in situations where the number of characters is extremely large and the existing classification is extremely imperfect. New cladograms formed by cladistic analysis have successfully demonstrated that many previously recognized taxa are actually polyphyletic. However, the translation of detailed analyses into absolutely corresponding classifications, such as Rosen's (1973) classification of higher teleosts, has led to a large number of new usages of previously existing taxonomic names and the creation of many new names,S Adenosyl Methionine, as well as the introduction of many new hierarchical levels. This method was objected to as manifestly inconsistent with the purpose that the classification should be simple, but bonde (1974:567) retorted that it was not a "correct argument against Henniker's theory." It seems that this is not against cladistic analysis, but against cladistic classification. pioneer-biotech.com

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