Biology & Philosophy

, Volume 25, Issue 4, pp 569–588 | Cite as

The myth of bacterial species and speciation

  • Jeffrey G. LawrenceEmail author
  • Adam C. Retchless


The Tree of Life hypothesis frames the evolutionary process as a series of events whereby lineages diverge from one another, thus creating the diversity of life as descendent lineages modify properties from their ancestors. This hypothesis is under scrutiny due to the strong evidence for lateral gene transfer between distantly related bacterial taxa, thereby providing extant taxa with more than one parent. As a result, one argues, the Tree of Life becomes confounded as the original branching structure is gradually superseded by reticulation, ultimately losing its ability to serve as a model for bacterial evolution. Here we address a more fundamental issue: is there a Tree of Life that results from bacterial evolution without considering such lateral gene transfers? Unlike eukaryotic speciation events, lineage separation in bacteria is a gradual process that occurs over tens of millions of years, whereby genetic isolation is established on a gene-by-gene basis. As a result, groups of closely related bacteria, while showing robust genetic isolation as extant lineages, were not created by an unambiguous series of lineage-splitting events. Rather, a temporal fragmentation of the speciation process results in cognate genes showing different genetic relationships. We argue that lineage divergence in bacteria does not produce a tree-like framework, and inferences drawn from such a framework have the potential to be incorrect and misleading. Therefore, the Tree of Life is an inappropriate paradigm for bacterial evolution regardless of the extent of gene transfer between distantly related taxa.


Species Speciation Recombination Gene transfer Tree of Life 



This work was support by grant GM078092 from the National Institutes of Health. The paper was first presented at the workshop, Perspectives on the Tree of Life, sponsored by the Leverhulme Trust and held in Halifax, Nova Scotia, July, 2009.


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Copyright information

© Springer Science+Business Media B.V. 2010

Authors and Affiliations

  1. 1.Department of Biological SciencesUniversity of PittsburghPittsburghUSA

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