Christopher D. Horvath

A review is presented of the various alternative conceptual definitions for biological species as well as of the contending theoretical explanations for the origin of species. This critical review elucidates a set of criteria that any adequate species concept must satisfy and a related set that must be satisfied by any adequate explanation of the speciation process. The result of this analysis is an argument that species are the natural products of biological processes and not artificial, human-constructed classes. Species are historical "individuals" with unique evolutionary pasts. These "individuals" consist of lineages of organisms related to one another in an ancestor-descendent relationship, and originating from a single "event" such as the acquisition of some reproductive isolation mechanism or an hybridization event between two local populations. These "individuals" are cladistically monophyletic. The study of the processes by which species originate and are maintained is the study of the biological forces that either keep a particular lineage together as an historical entity with an unique evolutionary identity, and/or that cause such lineages to dissolve and lose that unique identity. ;In addition, it is argued that a satisfactory understanding of the pattern of organization seen in the natural world , and of the processes by which this pattern evolves cannot be obtained independently of one another. Descriptions of dynamic patterns of organization, and explanations of the processes involved in creating and maintaining those patterns must constantly inform one another if a correct account of either is to be had. In order to avoid circularity in such investigations, independent experiments must be performed to verify our understanding of the patterns we are attempting to explain as well as our understanding of the processes hypothesized as explanations for those patterns

Treating species as individuals and not classes has been crucial to the integration of evolutionary theory with modern systematics. Despite the theoretically important role the concept of individuality plays in modern phylogenetic systematics and in evolutionary theory more generally, many have been content to rely on common-sense intuitions about what counts as an individual. One of the most often cited intuitions is that individuals should be defined intrinsically. Unfortunately, common-sense intuitions like this one have proven to be inadequate for identifying and characterizing historical individuals (like species). An examination of real-world biological examples shows that our common-sense intuitions are equally inadequate when applied to at least some biological organisms--the paradigm individuals

Species serve as both the basic units of macroevolutionary studies and as the basic units of taxonomic classification. In this paper I argue that the taxa identified as species by the Phylogenetic Species Concept (Mishler and Brandon 1987) are the units of biological organization most causally relevant to the evolutionary process but that such units exist at multiple levels within the hierarchy of any phylogenetic lineage. The PSC gives us no way of identifying one of these levels as the privileged level on which taxonomic classifications can be based.

While most researchers who use evolutionary theory to investigatehuman nature especially human sexuality describe themselves as ``interactionists'', there is no clear consensus on the meaning of thisterm in this context. By interactionism most people in the fieldmean something like, both nature and nurture ``count'' in thedevelopment of human psychology and behavior. Nevertheless, themultidisciplinary nature of evolutionary psychology results in a widevariety of interpretations of this general claim. Today, mostdebates within evolutionary psychology about the innateness of agiven behavioral characteristic or over its development turn as muchon which conception of ``innateness'' and ``interactionism'' theresearcher holds as on any empirical data they might derive.

Over the past several years, various operational definitions of gender have been used in studies of gender conformity in homosexual males. The goal of these studies is to demonstrate that childhood gender nonconformity (CGN) is either the proximate cause of adult homosexuality or an intermediate step in a biologically mediated process. The hypothesis of a causal connection between the development of gender and sexual orientation is embedded within the context of a biological (evolutionary) understanding of human behavior. Thus, testing the hypothesis of a causal connection between CGN and sexuality requires a concept of gender that is compatible with the basic principles of biological causation and our current understanding of evolutionary processes. I will argue that the concepts of gender used in the attempt to demonstrate a causal connection between CGN and sexual orientation are inappropriate because they provide no uniform, consistent method for identifying and measuring the biologically significant components of gender. I will also argue that the concept of gender that does emerge from these studies suggests an hypothesis about the connection between sexuality and gender that is not consistent with the cross-gendered theory of the etiology of homosexuality.