Biological Species Concept: The Most Widely Accepted Concept of Species

The term species is a Latin word meaning kinds. Species is a basic unit of biological classification as well as taxonomic rank. The scientific system of giving names to kinds of plants and animals revolves around the level of species. Early Greek philosophers such as Hippocrates, Plato and Aristotle also emphasized on the biological classification. Aristotle was considered as father of biological classification and he emphasized that all the parts of the body and activity should be considered during classification. As far as species is considered his idea was basically of essentialism or typological. Later on, in eighteenth century, the typological species concept also called as essentialism was elaborated by Linnaeus who was considered as father of taxonomy and proposed binomial nomenclature. In eighteenth century, a new concept of species called as Nominalistic species concept was suggested by Occam and his followers which was very popular in France. It states that nature produces individuals and nothing else. Species has no real existence in nature and it is only a mental concept. In seventeenth century, a new species concept began to emerge and it was Ray who believed in morphological species concept, but his species characteristics also contained the germ of biological species concept because he considered the reproductive relationship to be a principal species criterion. As early as 1760, Koelreutier also emphasized that all the individuals which are able to interbreed and produce fertile offspring belong to the same species. Other naturalists and taxonomists of nineteenth century such as Buffon, Merrem, Voigt, Walsh, and many others prepared the way for development of biological species concept. Charles Darwin who proposed the theory of origin of species by means of natural selection, appeared to have a morphological concept of species which was central to his theory of natural selection. However, later he gave importance to reproductive isolation and hence biological species concept. In his transmutation notebooks, Darwin realized the reality of species on the basis of criterion of non-interbreeding. As a consequence of this, biological species concept, Darwin recognized that acquisition of reproductive isolation was the mark of completion of transformation of permanent variety to the status of good species. Later on, biological species concept was emphasized and developed by Jordan, Mayr and Dobzhansky in the twentieth century. However, it has certain difficulties in its applications. According to this species concept, species is defined as a group of potentially or actually interbreeding natural populations which are reproductively isolated from other such groups. It was accepted as a most widely accepted definition of species. However, recently it has been criticized by molecular evolutionary biologists stating that “It is the time to abandon the biological species concept”. At the same time, it is also said that “No, it is not the time to abandon the BSC. The genic concept proposed by Wu goes against BSC but at the same time it has also been argued that none whole heartedly embraced the new genic concept of species. Recently, based on the work done on bacteria and viruses, it has been suggested that a single biological species definition once thought to be limited to sexually reproducing organisms, is applicable across all cellular and acellular life forms. Thus, there is a single universal definition of species across Life’s domain