Contemplating imaginary scenarios that evoke certain sorts of quasi-sensory intuitions may bring us to new beliefs about contingent features of the natural world. These beliefs may be produced quasi-observationally; the presence of a mental image may play a crucial cognitive role in the formation of the belief in question. And this albeit fallible quasi-observational belief-forming mechanism may, in certain contexts, be sufficiently reliable to count as a source of justification. This sheds light on the central puzzle surrounding scientific thought experiment, which is how contemplation of an imaginary scenario can lead to new knowledge about contingent features of the natural world.

Thought experiment acquires evidential significance only on particular metaphysical assumptions. These include the thesis that science aims at uncovering “phenomena”—universal and stable modes in which the world is articulated—and the thesis that phenomena are revealed imperfectly in actual occurrences. Only on these Platonically inspired assumptions does it make sense to bypass experience of actual occurrences and perform thought experiments. These assumptions are taken to hold in classical physics and other disciplines, but not in sciences that emphasize variety and contingency, such as Aristotelian natural philosophy and some forms of historiography. This explains why thought experiments carry weight in the former but not the latter disciplines.

Sewall Wright's adaptive landscape is the most influential heuristic in evolutionary biology. Wright's biographer, Provine, criticized Wright's adaptive landscape, claiming that its heuristic value is dubious because of deep flaws. Ruse has defended Wright against Provine. Ruse claims Provine has not shown Wright's use of the landscape is flawed, and that, even if it were, it is heuristically valuable. I argue that both Provine's and Ruse's analyses of the adaptive landscape are defective and suggest a more adequate understanding of it.

Ernst Mayr has criticised the methodology of population genetics for being essentialist: interested only in “types” as opposed to individuals. In fact, he goes so far as to claim that “he who does not understand the uniqueness of individuals is unable to understand the working of natural selection” (1982, 47). This is a strong claim indeed especially since many responsible for the development of population genetics (especially Fisher, Haldane, and Wright) were avid Darwinians. In order to unravel this apparent incompatibility I want to examine the possible sources and implications of essentialism in this context and show why the kind of mathematical analysis found in Fisher's work is better seen as responsible for extending the theory of natural selection to a broader context rather than inhibiting its applicability.

The recent literature in philosophy of biology has drawn attention to the different sorts of explanations proffered in the biological sciences—we have molecular, biomedical, and evolutionary explanations. Do these explanations all have a common structure or relation that they seek to capture? This paper will answer in the negative. I defend a pluralistic and pragmatic approach to explanation. Using examples from classical population genetics, I argue that formal demonstrations, and even strictly “mathematical truths,” may serve as explanatory in different historical contexts.

This paper analyzes the development of evolutionary theory in the period from 1918 to 1932. It argues that: (i) Fisher's work in 1918 constituted a not fully satisfactory reduction of biometry to Mendelism; (ii) there was a synthesis in the 1920s but that this synthesis was mainly one of classical genetics with population genetics, with Haldane's The Causes of Evolution being its founding document; (iii) the most important achievement of the models of theoretical population genetics was to show that natural selection sufficed as a mechanism for evolution; and (iv) Haldane formulated a prospective evolutionary theory in the 1920s whereas Fisher and Wright formulated retrospective theories of evolutionary history.

Given its importance in modern physics, philosophers of science have paid surprisingly little attention to the subject of symmetries and invariances, and they have largely neglected the subtopic of symmetry breaking. I illustrate how the topic of laws and symmetries brings into fruitful interaction technical issues in physics and mathematics with both methodological issues in philosophy of science, such as the status of laws of physics, and metaphysical issues, such as the nature of objectivity.