Political arguments about biodiversity and the preservation of endangered species generally assume we know what a species is. Yet answering the question of what constitutes a "good" species has long been a confusing and controversial exercise. Within ornithological circles, the debate over the "species question" has often been described as being between population in which members share a distinctive, genetically traceable feature that distinguishes it from other populations.
The late Charles G. Sibley, a prominent ornithologist and one of the fomenters of a controversial revolution in avian taxonomy, could be called a splitter. He used a process known as DNA-DNA hybridization—which compares DNA from different species—to determine the relationships of the various families of birds. From his studies he concluded vultures, and that loons and grebes, which many taxonomists had argued were closely related, were not.
Sibley's work has not been widely accepted. "What the DNA data can give you is an approximation of how different the genes of two isolated populations are," one critic has written, "but how you interpret those differences is basically arbitrary, as arbitrary as any decision made in any species concept." Sibley might examples in nature of populations that refuse to fit our limited set of definitions and names."
Whatever the merits of each position, the species question undoubtedly has political and economic stakes. For example, increasing the number of species would needing protection as well.
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