Marc Ereshefsky

The issue of whether species are individuals is now an old one; the literature abounds with arguments, counter-arguments and counter-counter-arguments for their individuality. The question I want to take up in this paper is not whether species are indeed individuals, but what ramifications their alleged individuality has for macroevolutionary theory.According to those biologists who argue for a new theory of macroevolution, the individuality of species is one of the fundamental premises of that theory. For example, Joel Cracraft writes of himself and others thatThe issue of individuality… is at the heart of arguments of those evolutionary biologists who see a need to view the patterns and processes of evolution as being hierarchically arranged into microevolutionary and macroevolutionary levels (1987, p. 332).

This paper examines David Hull’s and Peter Godfrey-Smith’s accounts of biological individuality using the case of biofilms. Biofilms fail standard criteria for individuality, such as having reproductive bottlenecks and forming parent-offspring lineages. Nevertheless, biofilms are good candidates for individuals. The nature of biofilms shows that Godfrey-Smith’s account of individuality, with its reliance on reproduction, is too restrictive. Hull’s interactor notion of individuality better captures biofilms, and we argue that it offers a better account of biological individuality. However, Hull’s notion of interactor needs more precision. We suggest some ways to make Hull’s notion of interactor and his account of individuality more precise. Generally, we maintain that biofilms are a good test case for theories of individuality, and a careful examination of biofilms furthers our understanding of biological individuality

Homeostatic Property Cluster (HPC) theory suggests that species and other biological taxa consist of organisms that share certain similarities. HPC theory acknowledges the existence of Darwinian variation within biological taxa. The claim is that “homeostatic mechanisms” acting on the members of such taxa nonetheless ensure a significant cluster of similarities. The HPC theorist’s focus on individual similarities is inadequate to account for stable polymorphism within taxa, and fails properly to capture their historical nature. A better approach is to treat distributions of traits in species populations as irreducible facts, explained in terms of selection pressures, genealogy, and other evolutionary factors. We call this view Population Structure Theory (PST). PST accommodates the view, implicit in biological systematics, that species are identified by reference to particular historical populations.

Richard Boyd’s Homeostatic Property Cluster Theory is becoming the received view of natural kinds in the philosophy of science. However, a problem with HPC Theory is that it neglects many kinds highlighted by scientific classifications while at the same time endorsing kinds rejected by science. In other words, there is a mismatch between HPC kinds and the kinds of science. An adequate account of natural kinds should accurately track the classifications of successful science. We offer an alternative account of natural kinds that better recognizes the diversity of epistemic aims scientists have for constructing classifications. That account introduces the idea of a classificatory program and provides criteria for judging whether a classificatory program identifies natural kinds.

Non-epistemic values play important roles in classificatory practice, such that philosophical accounts of kinds and classification should be able to accommodate them. Available accounts fail to do so, however. Our aim is to fill this lacuna by showing how non-epistemic values feature in scientific classification, and how they can be incorporated into a philosophical theory of classification and kinds. To achieve this, we present a novel account of kinds and classification, discuss examples from biological classification where non-epistemic values play decisive roles, and show how this account accommodates the role of non-epistemic values.

We introduce a dynamic model for evolutionary games played on a network where strategy changes are correlated according to degree of influence between players. Unlike the notion of stochastic stability, which assumes mutations are stochastically independent and identically distributed, our framework allows for the possibility that agents correlate their strategies with the strategies of those they trust, or those who have influence over them. We show that the dynamical properties of evolutionary games, where such influence neighborhoods appear, differ dramatically from those where all mutations are stochastically independent, and establish some elementary convergence results relevant for the evolution of social institutions.

How should we define ‘health’ and ‘disease’? There are three main positions in the literature. Naturalists desire value-free definitions based on scientific theories. Normativists believe that our uses of ‘health’ and ‘disease’ reflect value judgments. Hybrid theorists offer definitions containing both normativist and naturalist elements. This paper discusses the problems with these views and offers an alternative approach to the debate over ‘health’ and ‘disease’. Instead of trying to find the correct definitions of ‘health’ and ‘disease’ we should explicitly talk about the considerations that are central in medical discussions, namely state descriptions and normative claims . This distinction avoids the problems facing the major approaches to defining ‘health’ and ‘disease’, and it more clearly captures what matters in medical discussions

Environmental philosophers spend considerable time drawing the divide between humans and the rest of nature. Some argue that humans and our actions are unnatural. Others allow that humans are natural, but maintain that humans are nevertheless distinct. The motivation for distinguishing humans from the rest of nature is the desire to determine what aspects of the environment should be preserved. The standard view is that we should preserve those aspects of the environment outside of humans and our influence. This paper examines the standard view by asking two questions. First, are the suggested grounds for distinguishing humans from the rest of the environment viable? Second, is such a distinction even needed for determining what to preserve? The paper concludes that debates over whether humans are natural and whether humans are unique are unhelpful when deciding what to preserve.

A standard requirement on natural kinds is that they be mind independent. However, many kinds in the human and social sciences, even the natural sciences, depend on human thought. This article suggests that the mind independence requirement on natural kinds be replaced with the requirement that natural kind classifications be defeasible. The defeasibility requirement does not require that natural kinds be mind independent, so it does not exclude mind dependent scientific kinds from being natural kinds. Furthermore, the defeasibility requirement captures the idea that natural kind classifications are tools for investigating the empirical world.

Traditionally, species have been treated by biologists and philosophers as natural kinds. However, this conception of species has posed several problems for evolutionary theory. For example, biologists have been hard pressed to find traits had by all and only the members of a species. This has caused some philosophers to doubt that evolutionary theory is a scientific theory. ;In an effort to resolve such problems, Michael Ghiselin and David Hull have argued that species are not kinds but individuals. A number of authors have adopted this conclusion. Some have even gone on to argue that besides showing that species are not kinds, the thesis that species are individuals has other ramifications for evolutionary theory. For example, the thesis is said to lend support to the Theory of Punctuated Equilibrium. ;In my dissertation, I argue that while species are not kinds, most species are not individuals either. Furthermore, even if all species were individuals, the alleged ramifications are not forthcoming. ;More specifically, in Chapter One I review the arguments against species being kinds and the recent replies to those arguments. I also examine the nature of kinds and contend that the original arguments against species being kinds still stand. ;In Chapter Two, I turn to the metaphysics of individuality. I argue that mere spatiotemporal continuity and a rough similarity among the constituents of an entity are insufficient for it to be an individual. The constituents of an individual must be appropriately causally connected as well. ;With this requirement, I return to species in Chapter Three. Most species consist of subpopulations which are not causally connected in any biological fashion. Because of this, and other reasons, I argue that most species are not individuals. ;In the final chapter, I point out that the result of the previous chapter goes against the claim that what distinguishes species from higher taxa is that species and not higher taxa are individuals. I also argue that even if all species were individuals, their individuality does not support the Theory of Punctuated Equilibrium. Finally, some authors maintain that a unit of selection must be an individual. I argue that there is no such requirement on units of selection

This paper clarifies the historical nature of species by showing that species are path-dependent entities. A species’ identity is not determined by its intrinsic properties or its origin, but by its unique evolutionary path. Seeing that species are path-dependent entities has three implications: it shows that origin essentialism is mistaken, it rebuts two challenges to the species-are-historical-entities thesis, and it demonstrates that the identity of a species during speciation depends on future events

This paper examines the species problem in microbiology and its implications for the species problem more generally. Given the different meanings of ‘species’ in microbiology, the use of ‘species’ in biology is more multifarious and problematic than commonly recognized. So much so, that recent work in microbial systematics casts doubt on the existence of a prokaryote species category in nature. It also casts doubt on the existence of a general species category for all of life (one that includes both prokaryotes and eukaryotes). Prokaryote biology also undermines recent attempts to save the species category, such as the suggestion that species are metapopulation lineages and the idea that ‘species’ is a family resemblance concept.

Paul Thompson, John Beatty, and Elisabeth Lloyd argue that attempts to resolve certain conceptual issues within evolutionary biology have failed because of a general adherence to the received view of scientific theories. They maintain that such issues can be clarified and resolved when one adopts a semantic approach to theories. In this paper, I argue that such conceptual issues are just as problematic on a semantic approach. Such issues arise from the complexity involved in providing formal accounts of theoretical laws and scientific explanations. That complexity is due to empirical and pragmatic considerations, not one's adherence to a particular formal approach to theories. This analysis raises a broader question. How can any formal account properly represent the complex nature of empirical phenomena?

Several authors have argued for taxonomic pluralism in biology -the position that there is a plurality of equally legitimate classifications of the organic world. Others have objected that such pluralism boils down to a position of anything goes. This paper offers a response to the anything goes objection by showing how one can be a discerning pluralist. In particular, methodological standards for choosing taxonomic projects are derived using Laudan's normative naturalism. This paper also sheds light on why taxonomic pluralism occurs in biology as well as illustrates the usefulness of normative naturalism

A number of authors have argued that the thesis that species are individuals has important implications for macroevolutionary theory. More specifically, some authors claim that the thesis lends support to the Theory of Punctuated Equilibrium and indicates the existence of species selection. In this paper, I argue that the alleged individuality of species is neither necessary nor sufficient for the truth of that theory or for the existence of species selection. I also argue, contrary to the claims of some, that the individuality of a group is not a necessary requirement for a group to be a unit of selection.

The received view in the philosophy of biology is that biological taxa (species and higher taxa) do not have essences. Recently, some philosophers (Boyd, Devitt, Griffiths, LaPorte, Okasha, and Wilson) have suggested new forms of biological essentialism. They argue that according to these new forms of essentialism, biological taxa do have essences. This article critically evaluates the new biological essentialism. This article’s thesis is that the costs of adopting the new biological essentialism are many, yet the benefits are none, so there is no compelling reason to resurrect essentialism concerning biological taxa.

A number of authors argue that while species are evolutionary units, individuals and real entities, higher taxa are not. I argue that drawing the divide between species and higher taxa along such lines has not been successful. Common conceptions of evolutionary units either include or exclude both types of taxa. Most species, like all higher taxa, are not individuals, but historical entities. Furthermore, higher taxa are neither more nor less real than species. None of this implies that there is no distinction between species and higher taxa; the point is that such a distinction is more subtle than many authors have claimed.

Darwin offered an intriguing answer to the species problem. He doubted the existence of the species category as a real category in nature, but he did not doubt the existence of those taxa called ‘‘species’’. And despite his scepticism of the species category, Darwin continued using the word ‘‘species’’. Many have said that Darwin did not understand the nature of species. Yet his answer to the species problem is both theoretically sound and practical. On the theoretical side, DarwinÕs answer is confirmed by contemporary biology, and it offers a more satisfactory answer to the species problem than recent attempts to save the species category. On the practical side, DarwinÕs answer frees us from the search for the correct theoretical definition of ‘‘species’’. But at the same time it does not require that we banish the word ‘‘species’’ from biology as some recent sceptics of the species category advocate. Ó The Willi Hennig Society 2010