The concept of a species, a distinct type of organism, is associated in the minds of many with Charles Darwin and his seminal work, The Origin of Species; but the concept had been developing for many years before Darwin. Indeed, discussion of the problem of classification of the natural world could be traced back at least to ancient Greece, with Aristotle, in particular, providing detailed work on taxonomy. But for several centuries before Darwin's watershed work on natural selection, modern science had been improving upon Aristotle's work and two of the key figures involved were George-Louis Leclerc (the Comte de Buffon), and Carl Linnaeus.
Buffon was the eighteenth century French naturalist whose work would influence biologists for several generations into the future, including such significant figures as Jean-Baptiste Lamarck and even Charles Darwin himself. Indeed Darwin credited Buffon explicitly in the foreword to The Origin of Species, saying that Buffon was the first modern author to treat evolution in a scientific spirit.
But what was it about Buffon's work that was so significant to the development of the definition of species? At the heart of Buffon's legacy was his huge work, Histoire Naturelle, Generale et Particuliere (1749-1778), weighing in at 36 volumes with another 8 supplementaries. In this, he made a comprehensive account of biological knowledge up to that time. From these studies he developed the idea that different regions, although perhaps having similar environments, have their own distinct plants and animals, a position that would become known as Buffon's law. He drew the conclusion that organisms improved or degenerated after leaving some common centre and that much of this was driven by changes in climate.
Also working in the eighteenth century the Swedish biologist, Carl Linnaeus, performed foundational work in the construction of the binomial system of classification and this earned him the accolade of being the father of modern taxonomy. This binomial nomenclature is still used today and involves the naming of an organism using a Latin name that refers to its genus and species, with the genus being capitalized and the species being lower case. A familiar example of this is Homo sapiens, the scientific name for human beings, with Homo being the genus and sapiens the species.
During the late eighteenth century, Linnaeus played a major part in the massive expansion of biological knowledge during this period. His Linnaean taxonomy system was to be central to these efforts to classify all organisms. This featured a hierarchy of categories with which to classify organisms such as Kingdom, Phylum, Class, Order, Family, Genus, and Species. This system is still widely used today, with embellishments, although recent work by Woese et al (1990), based on new genetic data, sees the top level classification as having Three Domains the Eukaryotes, Archae, and Bacteria.