Confusion On The Meaning of "Species"
Species is one of several ranks in the hierarchical system of scientific classification, called taxonomic ranks.
Even though it is not disputed that species is a taxonomic rank, this does not prevent disagreements when particular species are discussed. Consider the case of the Baltimore Oriole and Bullock's Oriole, two similar species of birds that have sometimes in the past been considered to be one single species, the Northern Oriole. Currently, biologists agree that these are actually two separate species, but in the past this was not the case.
Disagreements and confusion happen over just what the best criteria are for identifying new species. In 1942, Ernst Mayr wrote that, because biologists have different ways of identifying species, they actually have different species concepts. Mayr listed five different species concepts, and since then many more have been added. The question of which species concept is best has occupied many printed pages and many hours of discussion.
The debates are philosophical in nature. One common disagreement is over whether a species should be defined by the characteristics that biologists use to identify the species, or whether a species is an evolving entity in nature. Every named species has been formally described as a type of organism with particular defining characteristics. These defining traits are used to identify which species an organism belongs to. For many species, all of the individuals that fit the defining criteria also make up a single evolving unit, but it might not be known whether that is the case. These two different ways of thinking about species, as a category or as an evolving population, may be quite different from each other.
Read more about this topic: Species Problem
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