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Evolution under our feet: Anthony David Bradshaw (1926-2008) and the rise of ecological genetics

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How fast is evolution? In this dissertation I document a profound change that occurred around the middle of the 20th century in the way that ecologists conceptualized the temporal and

How fast is evolution? In this dissertation I document a profound change that occurred around the middle of the 20th century in the way that ecologists conceptualized the temporal and spatial scales of adaptive evolution, through the lens of British plant ecologist Anthony David Bradshaw (1926–2008). In the early 1960s, one prominent ecologist distinguished what he called “ecological time”—around ten generations—from “evolutionary time”— around half of a million years. For most ecologists working in the first half of the 20th century, evolution by natural selection was indeed a slow and plodding process, tangible in its products but not in its processes, and inconsequential for explaining most ecological phenomena. During the 1960s, however, many ecologists began to see evolution as potentially rapid and observable. Natural selection moved from the distant past—a remote explanans for both extant biological diversity and paleontological phenomena—to a measurable, quantifiable mechanism molding populations in real time.

The idea that adaptive evolution could be rapid and highly localized was a significant enabling condition for the emergence of ecological genetics in the second half of the 20th century. Most of what historians know about that conceptual shift and the rise of ecological genetics centers on the work of Oxford zoologist E. B. Ford and his students on polymorphism in Lepidotera, especially industrial melanism in Biston betularia. I argue that ecological genetics in Britain was not the brainchild of an infamous patriarch (Ford), but rather the outgrowth of a long tradition of pastureland research at plant breeding stations in Scotland and Wales, part of a discipline known as “genecology” or “experimental taxonomy.” Bradshaw’s investigative activities between 1948 and 1968 were an outgrowth of the specific brand of plant genecology practiced at the Welsh and Scottish Plant Breeding stations. Bradshaw generated evidence that plant populations with negligible reproductive isolation—separated by just a few meters—could diverge and adapt to contrasting environmental conditions in just a few generations. In Bradshaw’s research one can observe the crystallization of a new concept of rapid adaptive evolution, and the methodological and conceptual transformation of genecology into ecological genetics.

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  • 2015

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Advancing the causal theory of natural selection

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The Modern Synthesis embodies a theory of natural selection where selection is to be fundamentally understood in terms of measures of fitness and the covariance of reproductive success and trait

The Modern Synthesis embodies a theory of natural selection where selection is to be fundamentally understood in terms of measures of fitness and the covariance of reproductive success and trait or character variables. Whether made explicit or left implicit, the notion that selection requires that some trait variable cause reproductive success has been deemphasized in our modern understanding of exactly what selection amounts to. The dissertation seeks to advance a theory of natural selection that is fundamentally causal. By focusing on the causal nature of natural selection (rather than on fitness or statistical formulae), certain conceptual and methodological problems are seen in a new, clarifying light and avenues toward new, interesting solutions to those problems are illustrated. First, the dissertation offers an update to explicitly causal theories of when exactly a trait counts as an adaptation upon fixation in a population and draws out theoretical and practical implications for evolutionary biology. Second, I examine a case of a novel character that evolves by niche construction and argue that it evolves by selection for it and consider implications for understanding adaptations and drift. The third contribution of the dissertation is an argument for the importance of defining group selection causally and an argument against model pluralism in the levels of selection debate. Fourth, the dissertation makes a methodological contribution. I offer the first steps toward an explicitly causal methodology for inferring the causes of selection—something often required in addition to inferring the causes of reproductive success. The concluding chapter summarizes the work and discusses potential paths for future work.

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  • 2016