Human behavior is the joint product of (i) contingencies of survival responsible for natural selection, and (ii) contingencies of reinforcement responsible for the repertoires of individuals, including (iii) the special contingencies maintained by an evolved social environment. Selection by consequences is a causal mode found only in living things, or in machines made by living things. It was first recognized in natural selection: Reproduction, a first consequence, led to the evolution of cells, organs, and organisms reproducing themselves under increasingly diverse (...) conditions. The behavior functioned well, however, only under conditions similar to those under which it was selected.Reproduction under a wider range of consequences became possible with the evolution of processes through which organisms acquired behavior appropriate to novel environments. One of these, operant conditioning, is a second kind of selection by consequences: New responses could be strengthened by events which followed them. When the selecting consequences are the same, operant conditioning and natural selection work together redundantly. But because a species which quickly acquires behavior appropriate to an environment has less need for an innate repertoire, operant conditioning could replace as well as supplement the natural selection of behavior.Social behavior is within easy range of natural selection, because other members are one of the most stable features of the environment of a species. The human species presumably became more social when its vocal musculature came under operant control. Verbal behavior greatly increased the importance of a third kind of selection by consequences, the evolution of social environments or cultures. The effect on the group, and not the reinforcing consequences for individual members, is responsible for the evolution of culture. (shrink)

An examination of the post-Darwinian history of biological taxonomy reveals an implicit assumption that the definitions of taxon names consist of lists of organismal traits. That assumption represents a failure to grant the concept of evolution a central role in taxonomy, and it causes conflicts between traditional methods of defining taxon names and evolutionary concepts of taxa. Phylogenetic definitions of taxon names (de Queiroz and Gauthier 1990) grant the concept of common ancestry a central role in the definitions of taxon (...) names and thus constitute an important step in the development of phylogenetic taxonomy. By treating phylogenetic relationships rather than organismal traits as necessary and sufficient properties, phylogenetic definitions remove conflicts between the definitions of taxon names and evolutionary concepts of taxa. The general method of definition represented by phylogenetic definitions of clade names can be applied to the names of other kinds of composite wholes, including populations and biological species. That the names of individuals (composite wholes) can be defined in terms of necessary and sufficient properties provides the foundation for a synthesis of seemingly incompatible positions held by contemporary individualists and essentialists concerning the nature of taxa and the definitions of taxon names. (shrink)

An examination of the post-Darwinian history of biological taxonomy reveals an implicit assumption that the definitions of taxon names consist of lists of organismal traits. That assumption represents a failure to grant the concept of evolution a central role in taxonomy, and it causes conflicts between traditional methods of defining taxon names and evolutionary concepts of taxa. Phylogenetic definitions of taxon names (de Queiroz and Gauthier 1990) grant the concept of common ancestry a central role in the definitions of taxon (...) names and thus constitute an important step in the development of phylogenetic taxonomy. By treating phylogenetic relationships rather than organismal traits as necessary and sufficient properties, phylogenetic definitions remove conflicts between the definitions of taxon names and evolutionary concepts of taxa. The general method of definition represented by phylogenetic definitions of clade names can be applied to the names of other kinds of composite wholes, including populations and biological species. That the names of individuals (composite wholes) can be defined in terms of necessary and sufficient properties provides the foundation for a synthesis of seemingly incompatible positions held by contemporary individualists and essentialists concerning the nature of taxa and the definitions of taxon names. (shrink)

Classifying is a fundamental operation in the acquisition of knowledge. Taxonomic theory can help students of cognition, evolutionary psychology, ethology, anatomy, and sociobiology to avoid serious mistakes, both practical and theoretical. More positively, it helps in generating hypotheses useful to a wide range of disciplines. Composite wholes, such as species and societies, are “individuals” in the logical sense, and should not be treated as if they were classes. A group of analogous features is a natural kind, but a group of (...) homologous features is not. Imposing hypotheses justified only on the basis of nominalist, realist, phenomenalist, or conceptualist metaphysics upon the neurophysiology of organisms or upon the causes of behavior exemplifies the “psychologist's fallacy” of William James. Levels should be distinguished from their members and from classes of levels, and the ontological status of entities ranked at levels should be made clear. It is important not to confuse such categories as substance and process with one another. Several genetical terms, such as “gene” and chromosome,” are even more equivocal than has been realized. Discussions about units of selection, behavior, and thinking suffer from the ambiguity of a “unit of” an entity. An important source of misunderstanding about natural selection is the habit of treating it as an “agent”: in an important sense, natural selection does not “act” at all. (shrink)

Numerous concepts exist for biological species. This diversity of ideas derives from a number of sources ranging from investigative study of particular taxa and character sets to philosophical aptitude and world view to operationalism and nomenclatorial rules. While usually viewed as counterproductive, in reality these varied concepts can greatly enhance our efforts to discover and understand biological diversity. Moreover, this continued "turf war" and dilemma over species can be resolved if the various concepts are viewed in a hierarchical system and (...) each evaluated for its inherent level of consilience. Under this paradigm a theoretically appropriate, highly consilient concept of species capable of colligating the abundant types of species diversity offers the best guidance for developing and employing secondary operational concepts for identifying diversity. Of all the concepts currently recognized, only the non-operational Evolutionary Species Concept corresponds to the requisite parameters and, therefore, should serve as the theoretical concept appropriate for the category Species. As operational concepts, the remaining ideas have been incompatible with one another in their ability to encompass species diversity because each has restrictive criteria as to what qualifies as a species. However, the operational concepts can complement one another and do serve a vital role under the Evolutionary Species Concept as fundamental tools necessary for discovering diversity compatible with the primary theoretical concept. Thus, the proposed hierarchical system of primary and secondary concepts promises both the most productive framework for mutual respect for varied concepts and the most efficient and effective means for revealing species diversity. (shrink)

Taxonomies of living things and the methods used to produce them changed little with the institutionalization of evolutionary thinking in biology. Instead, the relationships expressed in existing taxonomies were merely reinterpreted as the result of evolution, and evolutionary concepts were developed to justify existing methods. I argue that the delay of the Darwinian Revolution in biological taxonomy has resulted partly from a failure to distinguish between two fundamentally different ways of ordering identified by Griffiths : classification and systematization. Classification consists (...) of ordering entities into classes, groups defined by the attributes of their members; in contrast, systematization consists of ordering entities into systems, more inclusive entities whose existence depends on some natural process through which their parts are related. Evolutionary, or phylogenetic, systematics takes evolutionary descent to be the natural process of interest in biological taxonomy. I outline a general framework for a truly phylogenetic systematics and examine some of its consequences. (shrink)