Are Species Really Individuals?

Abstract

Hull, David L. (Department of Philosophy, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin 53201) 1976. Are species really individuals? Syst. Zool. 25:174-191.The processes which contribute to the evolution of biological species take place at a variety of levels of organization; e.g., genes give rise to other genes, organisms give rise to other organisms, and species give rise to other species. All of these processes require continuity through descent. If species are to be units of evolution, they need not be composed of similar organisms; instead they must be made up of organisms related by descent. Taxonomists do not impose this requirement on the phenomena; rather it follows from the nature of the evolutionary process itself. In addition to spatiotemporal continuity, species must also possess a certain degree of unity-to function as units of evolution. Gene exchange is one means by which such unity can be promoted. The mechanisms by which asexual species maintain a similar unity are problematic; higher taxa pose an even more serious problem. However, if species are chunks of the genealogical nexus, they cannot be viewed as classes. Instead they possess all the characteristics of individuals-that is, if organisms are taken to be paradigm individuals. The major difference between organisms and species as individuals is that organisms possess a largely fixed genetic makeup which constrains their development, whereas species do not. If species are individuals, then their names are most naturally viewed as proper names, names which denote particular individuals but do not possess any intensional meaning. [Species; evolution.] In a series of publications, Ghiselin (1966, 1969, 1974) has argued that species as chunks of the genealogical nexus are individuals, not classes of similar things, and that their names are proper names to be defined ostensively in a manner analogous to a christening (also Lother, 1972; Griffiths, 1974). Ghiselin's argument has two parts. The first is that the basic unit of classification must be some basic unit of evolution. Some biologists maintain that scientific theories are so variable and require data which is so difficult to obtain that classification should be theoretically neutral; no theoretical considerations should ever intrude during the formative stages of classification although theoretical inferences may be drawn from the classification afterwards. For these biologists, Ghiselin's position will seem wrong-headed, but it must be taken seriously by those biologists who believe that biological classifications must be in some sense evolutionary. The second part of Ghiselin's argument depends upon a particular view of meaning and definition. On this view, the names of individuals are proper names and, as such, have no meaning in the sense that terms like triangle, gold, and game do. They are meaningless identification tags and nothing else. They have no verbal definitions, no intensions. The twist which Ghiselin adds to the usual story is that the names of particular species are proper names because species are individuals. On the traditional view, the species category is a class of classes defined in termns of properties which particular species possess (e.g., reproductive isolation), particular species are classes defined in terms of the properties which organisms possess (e.g., pigmented feathers), and particular organisms are individuals (e.g., Gargantua) whose names are not defined at all (Buck and Hull, 1966). The relation between organisms, species, and the species category is membership. An organism is a member of its species and each species is a member of the species category. On the view being urged in this paper, both particular species and the species category itself must be moved down one category level. Organisms remain individuals, but they are no longer members of their species. Instead an organism is part of a more inclu-