Date of this Version
EVOLUTION 3: 369-373. December, 1949.
In some respects, it is extremely unfortunate that names are ever attached either to ideas or objects. The false attachment of names to ideas or objects similar but not identical with the original can work harm far exceeding the benefits conferred by having a convenient label. The name "species" has come to such a state. As we shall see, a species, be it plant or animal, is a fiction, a mental construct without objective existence. Animal, and plant, lines of descent exist in a four-dimensional continuum. To set up species in this continuous line of descent, we must chop it into units, and in any such process the divisions are purely arbitrary. Available information makes such a view more or less self-evident. What, then, is a "species"? Instead of starting with an evolutionary line and dealing with it on the basis of preconceived concepts, working from the top down, so to speak, let us work from the bottom up.
Our contention is that "species" have only a subjective existence. Our real biological unit is the breeding population, since it is through this ever-changing unit that the germ-plasm is passed. Taxonomy takes no notice of the breeding population, but any permanently useful taxonomic system must take account of its existence and its significance. Species and subspecies are the units with which the taxonomist deals, but they are merely convenient labels for arbitrary groupings and have only a minimum of biological meaning.
With a reply by Ernst Mayr, American Museum of Natural History, and a rejoinder by Prof. Burma.