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The Concept and Causes of Microbial Species

Wilkins, John S. (2007) The Concept and Causes of Microbial Species. [Preprint]

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    Abstract

    Species concepts for bacteria and other microbes are contentious, because they are often asexual. There is a Problem of Homogeneity: every mutation in an asexual lineage forms a new strain, of which all descendents are clones until a new mutation occurs. We should expect that asexual organisms would form a smear or continuum. What causes the internal homogeneity of asexual lineages, if they are in fact homogeneous? Is there a natural “species concept” for “microbes”? Two main concepts devised for metazoans and metaphytes have been applied to bacteria. One is the Recombination Concept, a revised form of the Biological Species Concept in which the homogenizing mechanism is the sharing of genome fragments, somewhat akin to sexual recombination. The other is the Ecological Species Concept, in which the ecological niche is that which maintains lineages as cohesive. In this paper I will discuss these two concepts, and offer an underlying model that conjoins them, and consider the implications for species concepts in general. In short, my argument is that asexual species are instances of the most primitive and underived notion of species, which I will call “quasispecies”, following Eigen, and that sexual species are merely one derived kind of species. Moreover, I will argue that there is a continuum of recombination from simple viral models in which each strain is a clone, through to obligate recombination of 50% of the parents’ genome, and that consequently there is no sharp division between “microbial” and more familiar species.


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    Item Type: Preprint
    Additional Information: Forthcoming in History and Philosophy of the Life Sciences
    Keywords: species concept, microbes, later genetic transfer, quasispecies
    Subjects: Specific Sciences > Biology > Systematics
    Specific Sciences > Biology
    Depositing User: John S Wilkins
    Date Deposited: 09 Jul 2007
    Last Modified: 07 Oct 2010 11:15
    Item ID: 3426
    URI: http://philsci-archive.pitt.edu/id/eprint/3426

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