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Definitely directed evolution (1890-1926): the importance of variation in major evolutionary works by Theodor Eimer, Edward Drinker Cope, and Leo Berg

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This dissertation shows that the central conceptual feature and explanatory motivation of theories of evolutionary directionality between 1890 and 1926 was as follows: morphological variation in the developing organism limits the possible outcomes of evolution in definite directions. Put broadly,

This dissertation shows that the central conceptual feature and explanatory motivation of theories of evolutionary directionality between 1890 and 1926 was as follows: morphological variation in the developing organism limits the possible outcomes of evolution in definite directions. Put broadly, these theories maintained a conceptual connection between development and evolution as inextricably associated phenomena. This project develops three case studies. The first addresses the Swiss-German zoologist Theodor Eimer's book Organic Evolution (1890), which sought to undermine the work of noted evolutionist August Weismann. Second, the American paleontologist Edward Drinker Cope's Primary Factors (1896) developed a sophisticated system of inheritance that included the material of heredity and the energy needed to induce and modify ontogenetic phenomena. Third, the Russian biogeographer Leo Berg's Nomogenesis (1926) argued that the biological world is deeply structured in a way that prevents changes to morphology taking place in more than one or a few directions. These authors based their ideas on extensive empirical evidence of long-term evolutionary trajectories. They also sought to synthesize knowledge from a wide range of studies and proposed causes of evolution and development within a unified causal framework based on laws of evolution. While being mindful of the variation between these three theories, this project advances "Definitely Directed Evolution" as a term to designate these shared features. The conceptual coherence and reception of these theories shows that Definitely Directed Evolution from 1890 to 1926 is an important piece in reconstructing the wider history of theories of evolutionary directionality.

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Date Created
2014

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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 spatial scales of adaptive evolution, through the lens of British

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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Date Created
2015

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Evolutionary Genetics of CORL Proteins

Description

Transgenic experiments in Drosophila have proven to be a useful tool aiding in the

determination of mammalian protein function. A CNS specific protein, dCORL is a

member of the Sno/Ski family. Sno acts as a switch between Dpp/dActivin signaling.

dCORL is involved in

Transgenic experiments in Drosophila have proven to be a useful tool aiding in the

determination of mammalian protein function. A CNS specific protein, dCORL is a

member of the Sno/Ski family. Sno acts as a switch between Dpp/dActivin signaling.

dCORL is involved in Dpp and dActivin signaling, but the two homologous mCORL

protein functions are unknown. Conducting transgenic experiments in the adult wings,

and third instar larval brains using mCORL1, mCORL2 and dCORL are used to provide

insight into the function of these proteins. These experiments show mCORL1 has a

different function from mCORL2 and dCORL when expressed in Drosophila. mCORL2

and dCORL have functional similarities that are likely conserved. Six amino acid

substitutions between mCORL1 and mCORL2/dCORL may be the reason for the

functional difference. The evolutionary implications of this research suggest the

conservation of a switch between Dpp/dActivin signaling that predates the divergence of

arthropods and vertebrates.

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Date Created
2019