August Weismann is famous for having argued against the inheritance of acquired characters. However, an analysis of his work indicates that Weismann always held that changes in external conditions, acting during development, were the necessary causes of variation in the hereditary material. For much of his career he held that acquired germ-plasm variation was inherited. An irony, which is in tension with much of the standard twentieth-century history of biology, thus exists – Weismann was not a Weismannian. I distinguish three (...) claims regarding the germ-plasm: (1) its continuity, (2) its morphological sequestration, and (3) its variational sequestration. With respect to changes in Weismann’s views on the cause of variation, I divide his career into four stages. For each stage I analyze his beliefs on the relative importance of changes in external conditions and sexual reproduction as causes of variation in the hereditary material. Weismann believed, and Weismannism denies, that variation, heredity, and development were deeply intertwined processes. This article is part of a larger project comparing commitments regarding variation during the latter half of the nineteenth century. (shrink)

Ernst Mayr''s distinction between ultimate and proximate causes is justly considered a major contribution to philosophy of biology. But how did Mayr come to this philosophical distinction, and what role did it play in his earlier scientific work? I address these issues by dividing Mayr''s work into three careers or phases: 1) Mayr the naturalist/researcher, 2) Mayr the representative of and spokesman for evolutionary biology and systematics, and more recently 3) Mayr the historian and philosopher of biology. If we want (...) to understand the role of the proximate/ultimate distinction in Mayr''s more recent career as a philosopher and historian, then it helps to consider hisearlier use of the distinction, in the course of his research, and in his promotion of the professions of evolutionary biology and systematics. I believe that this approach would also shed light on some other important philosophical positions that Mayr has defended, including the distinction between essentialism: and population thinking. (shrink)

I have argued elsewhere that scientific realism is most significantly challenged neither by traditional arguments from underdetermination of theories by the evidence, nor by the traditional pessimistic induction, but by a rather different historical pattern: our repeated failure to conceive of alternatives to extant scientific theories, even when those alternatives were both (1) well-confirmed by the evidence available at the time and (2) sufficiently scientifically serious as to be later embraced by actual scientific communities. Here I use August Weismann's defense (...) of his influential germ-plasm theory of inheritance to support my claim that this pattern characterizes the history of theoretical scientific investigation generally. Weismann believed that the germ-plasm must become disintegrated into its constituent elements over the course of development, I argue, only because he failed to conceive of any possible alternative mechanism of ontogenetic differentiation. This and other features of the germ-plasm theory, I suggest, reflect a still more fundamental failure to imagine that the germ-plasm might be a productive rather than expendable resource for the cell. Weismann's case provides impressive support for the problem of unconceived alternatives while rendering its challenge to scientific realism deeper and sharper in a number of important ways. (shrink)

The Philosophy of Science, if the phrase were to be understood in the comprehensive sense which most naturally offers itself to our thoughts, ...