The goal of a phylogenetic species concept is to reveal the smallest units that are analysable by cladistic methods and interpretable as the result of phylogenctic history. We define species as the smallest aggregation of populations (sexual) or lineagcs (asexual) diagnosable by a unique combination of character states in comparable individuals (semaphoronts). A character state is an inherited attribute distributed among all comparable individuals (semaphoronts) of the same historical population, clade, or terminal lineage. This definition of species is character-based and (...) pattern oriented. Evolutionary explanations of phylogenetic species are consistent with contemporary explanations of processes of speciation, but require only the assumption of nested hierarchical pattern. We discuss the compatibility of the phylogenetic species concept with various biological needs for species and justify its use at the exclusion of alternative species concepts. (shrink)

In both folk taxonomy and science, the idea of species is based on the observation that phenotypic variation is discrete and not continuous. The definition of the species category, the "what," must therefore be restricted to these empirically demonstrable facts. To avoid circularity, concepts about the biological nature of species, the "whys," must be kept separate from the criteria by which individual species are circumscribed. Such ideas are models and can only be judged in terms of their capacity to bring (...) observations into a meaningful context. The Biological Species Concept (BSC), the Evolutionary Species Concept (EvSC) and the Ecological Species Concept (EcSC) are models, not definitions. The BSC has its principal flaw in its inability to deal with uniparentally reproducing organisms. It fails to identify the driving force of speciation. It therefore fails to predict diversity and to explain why different species have different reproductive strategies. The EvSC fails to explain why different lineages are phenetically different. It fails, therefore, to explain why species arise, and why there are differences in diversity and reproductive strategies. The EcSCh as the potential to make a direct connection between environment and phenetic variation patterns. It provides a useful conceptual framework for experimentation and observation at the interface between taxonomy and ecology and has the potential to explain on a universal basis variation in diversity and reproductive patterns. In some taxonomically difficult cases it also sheds light on the nature of variation patterns and might therefore help in taxonomic judgment where the BSC is conceptually inapplicable and the EvSC fails to provide useful concepts. (shrink)

The so-called ‘‘species problem’’ has plagued evolution- ary biology since before Darwin’s publication of the aptly titled Origin of Species. Many biologists think the problem is just a matter of semantics; others complain that it will not be solved until we have more empirical data. Yet, we don’t seem to be able to escape discussing it and teaching seminars about it. In this paper, I briefly examine the main themes of the biological and philosophical liter- atures on the species problem, (...) focusing on identifying common threads as well as relevant differences. I then argue two fundamental points. First, the species problem is not primarily an empirical one, but it is rather fraught with philosophical questions that require—but cannot be settled by—empirical evidence. Second, the (dis-)solution lies in explicitly adopting Wittgenstein’s idea of ‘‘family resemblance’’ or cluster concepts, and to consider spe- cies as an example of such concepts. This solution has several attractive features, including bringing together apparently diverging themes of discussion among bio- logists and philosophers. The current proposal is con- ceptually independent (though not incompatible) with the pluralist approach to the species problem advocated by Mishler, Donoghue, Kitcher and Dupre ́, which implies that distinct aspects of the species question need to be emphasized depending on the goals of the researcher. From the biological literature, the concept of species that most closely matches the philosophical discussion pre- sented here is Templeton’s cohesion idea. (shrink)

_Naming and Necessity_ has had a great and increasing influence. It redirected philosophical attention to neglected questions of natural and metaphysical necessity and to the connections between these and theories of naming, and of identity. This seminal work, to which today's thriving essentialist metaphysics largely owes its impetus, is here reissued in a newly corrected form with a new preface by the author. If there is such a thing as essential reading in metaphysics, or in philosophy of language, this is (...) it. (shrink)

A transcript of three lectures, given at Princeton University in 1970, which deals with (inter alia) debates concerning proper names in the philosophy of language.

Oaks exemplify problems with the reproductive species concept which motivate a reconsideration of the use and nature of species. Ecology is important in the reconsideration. The species level is usually overemphasized in evolutionary thought; selection acts on phenotypes and any mutualistic units. Standard definitions tend to inhibit free conceptual progress. Multispecies, sets of broadly sympatric species that exchange genes, may occur among animals as well as plants and may conceivably bridge kingdoms. This phenomenon can be adaptively important. There may be (...) taxa without species. The degree of modality of adaptive zones can be investigated empirically. (shrink)

Interprets biological theory while looking at work done on genetics, systematics and selection.