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Symbiosis, selection, and individuality


A recent development in biology has been the growing acceptance that holobionts, entities comprised of symbiotic microbes and their host organisms, are widespread in nature. There is agreement that holobionts are evolved outcomes, but disagreement on how to characterize the operation of natural selection on them. The aim of this paper is to articulate the contours of the disagreement. I explain how two distinct foundational accounts of the process of natural selection give rise to competing views about evolutionary individuality.

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  1. My use of the term “macrobe” follows Dupré and O’Malley (2012b).

  2. In pointing out the fact that branching cell-level lineages are inevitable I’m not taking sides in the debate about whether the “tree of cells” has some special importance for understanding prokaryotic evolution (see Lerat et al. 2005; Doolittle and Bapteste 2007; Doolittle 2009; Dupré 2012a).

  3. Zilber-Rosenberg and Rosenberg suggest that holobionts play the role of the interactor as well as the role of the replicator in evolution (Zilber-Rosenberg and Rosenberg 2008, 731). Replicators are typically taken to be entities that make high-fidelity copies of themselves (Dawkins 1976); it is hard to see how to make a case that holobionts fit the bill.

  4. It is worth noting the terminological nuances here: Dupré understands the lineage-based category to pick out, “the more traditionally conceived organisms,” whereas Godfrey-Smith understands traditional organismality in terms of metabolism, regardless of a metabolizer’s capacity to form lineages.


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Correspondence to Austin Booth.

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Booth, A. Symbiosis, selection, and individuality. Biol Philos 29, 657–673 (2014).

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  • Biological individuality
  • Units of selection
  • Symbiosis
  • Holobiont
  • Microbe