These days 'evolution' is usually defined as any change in the relative frequencies of genes in a population over time. This definition and some obvious alternatives are examined and rejected. The criticism of these definitions points out the need for a more holistic analysis of genotypes. I attempt such analysis by introducing measures of similarity of whole genotypes and then by grouping genotypes into similarity classes. Three sorts of measures of similarity are examined: a measure of structural similarity, a measure (...) of functional similarity and one of relational or historical similarity. The functional approach is shown to be superior and a definition of 'evolution' is suggested. (shrink)

Among the liveliest disputes in evolutionary biology today are disputes concerning the role of chance in evolution--more specifically, disputes concerning the relative evolutionary importance of natural selection vs. so-called "random drift". The following discussion is an attempt to sort out some of the broad issues involved in those disputes. In the first half of this paper, I try to explain the differences between evolution by natural selection and evolution by random drift. On some common construals of "natural selection", those two (...) modes of evolution are completely indistinguishable. Even on a proper construal of "natural selection", it is difficult to distinguish between the "improbable results of natural selection" and evolution by random drift. In the second half of this paper, I discuss the variety of positions taken by evolutionists with respect to the evolutionary importance of random drift vs. natural selection. I will then consider the variety of issues in question in terms of a conceptual distinction often used to describe the rise of probabilistic thinking in the sciences. I will argue, in particular, that what is going on here is not, as might appear at first sight, just another dispute about the desirability of "stochastic" vs. "deterministic" theories. Modern evolutionists do not argue so much about whether evolution is stochastic, but about how stochastic it is. (shrink)

There appears to be a wide measure of agreement, both amongst biologists and others, that Darwin's theory of evolution marks a major breakthrough in the science of biology; Darwin has even been called ‘Biology's Newton’, the highest term of praise that could be bestowed on a scientist. A. G. N. Flew, considering the matter from a philosophical point of view, says: ‘Yet one of the most important of all scientific theories is that developed by Darwin in his Origin of Species (...) . Covering the entire range of biological phenomena its scope is enormous. While if any scientific theory is interesting philosophically this one is.’ In spite of the testimony of both biologists and philosophers of science to the importance of the theory, it does not appear to play anything like the same role in biology as does Newton's theory in physics. For modern physics would be. (shrink)

Quine has developed two reasons for thinking that our ontology should not include the ontological category of properties. His first point is that the criterion for individuating properties is unclear, and the second is that postulating the existence of properties would not explain anything. In what follows I critically examine these two themes, which I will call the clarity argument and the parsimony argument. Although I will suggest that these two arguments are defective, I also will try to show that (...) certain related arguments on behalf of the existence of properties are likewise flawed. This will set the stage for the discussion in the fourth section of the perspective provided by evolutionary theory on the question of the ontological status of properties. It will emerge that evolutionary theory provides reason for thinking that properties exist, and, additionally, gives an interesting point of view on the epistemological and metaphysical issues that Quine has addressed. (shrink)

In the insightful and searching paper of Mills and Beatty the following definition of ‘fitness’, as the term figures in the theory of natural selection, is offered:The [individual] fitness of an organism x in environment E equals n =dfn is the expected number of descendants which x will leave in E.

The concept of "fitness" is a notion of central importance to evolutionary theory. Yet the interpretation of this concept and its role in explanations of evolutionary phenomena have remained obscure. We provide a propensity interpretation of fitness, which we argue captures the intended reference of this term as it is used by evolutionary theorists. Using the propensity interpretation of fitness, we provide a Hempelian reconstruction of explanations of evolutionary phenomena, and we show why charges of circularity which have been levelled (...) against explanations in evolutionary theory are mistaken. Finally, we provide a definition of natural selection which follows from the propensity interpretation of fitness, and which handles all the types of selection discussed by biologists, thus improving on extant definitions. (shrink)

A precise formulation of the structure of modern evolutionary theory has proved elusive. In this paper, I introduce and develop a formal approach to the structure of population genetics, evolutionary theory's most developed sub-theory. Under the semantic approach, used as a framework in this paper, presenting a theory consists in presenting a related family of models. I offer general guidelines and examples for the classification of population genetics models; the defining features of the models are taken to be their state (...) spaces, parameters, and laws. The suggestions regarding the various aspects of the characterization of population genetics models provide an outline for further detailed research. (shrink)

Even those generally skeptical of propensity interpretations of probability must now grant the following two points. First, the above single-case propensity interpretation meets recognized formal conditions for being a genuine interpretation of probability. Second, this interpretation is not logically reducible to a hypothetical relative frequency interpretation, nor is it only vacuously different from such an interpretation.The main objection to this propensity interpretation must be not that it is too vague or vacuous, but that it is metaphysically too extravagant. It asserts (...) not only that there are physical possibilities in nature, but further that nature itself contains innate tendencies toward these possibilities, tendencies which have the logical structure of probabilities. Thus the basic dispute between advocates of an actualist relative frequency interpretation and a single-case propensity interpretation is not a matter of epistemology, but metaphysics. The frequency theorist wishes to maintain that claims about physical probabilities are nothing more than claims about relative frequencies that will occur in the actual history of the world, be it infinite or no. It is a substantial, though hardly conclusive, argument for the propensity view that the mathematical structures commonly employed in studies of stochastic processes and statistical inference are richer than can be accommodated by a relative frequency interpretation. Whether it is possible to bridge this gap without going beyond an actualist metaphysics remains to be seen.38. (shrink)

Much if not most recent literature in philosophy of biology concerns the extent to which biological theories conform to what is known as the "received" philosophical view of scientific theories, a descendant of the logical-empiricist view of theories. But the received view currently faces a competitor--a very different view of theories known as the "semantic" view. It is argued here that the semantic view is more sensitive to the nature and limitations of evolutionary theory than is the received view. In (...) particular, the semantic view better accomodates the fact that evolutionary theory is bound to change as a result of the evolutionary process itself. This unusual feature of evolutionary theory provides a good reason for reconsidering the received view and paying close attention to the semantic view. (shrink)

The principle of natural selection is stated. It connects fitness values (actual reproductive success) with expected fitness values. The term 'adaptedness' is used for expected fitness values. The principle of natural selection explains differential fitness in terms of relative adaptedness. It is argued that this principle is absolutely central to Darwinian evolutionary theory. The empirical content of the principle of natural selection is examined. It is argued that the principle itself has no empirical biological content, but that the presuppositions of (...) its applicability are empirical. They form the empirical biological core of evolutionary theory. (shrink)