Making the most of clade selection

Clade selection is unpopular with philosophers who otherwise accept multilevel selection theory. Clades cannot reproduce, and reproduction is widely thought necessary for evolution by natural selection, especially of complex adaptations. Using microbial evolutionary processes as heuristics, I argue contrariwise, that (1) clade growth (proliferation of contained species) substitutes for clade reproduction in the evolution of complex adaptation, (2) clade-level properties favoring persistence – species richness, dispersal, divergence, and possibly intraclade cooperation – are not collapsible into species-level traits, (3) such properties can be maintained by selection on clades, and (4) clade selection extends the explanatory power of the theory of evolution

Microbial Evolution: Stalking the Wild Bacterial Species

SummaryA recent report suggests that, when habitats are disturbed, bacterial populations that would be considered to be separate species can merge, reversing the process of speciation. But, for bacteria, ‘species’ remains undefined and undefinable

Population Genomics: How Bacterial Species Form and Why They Don't Exist

SummaryTwo processes suggested to drive bacterial speciation — periodic selection and recombination — are generally thought to be mutually opposed. Recent work shows that data taken as evidence supporting the former may be explained by the latter, raising further problems for the idea of bacterial ‘species’

Speciation without Species: A Final Word

Here I present the several models currently popular for understanding speciation in prokaryotes, in particular bacteria. I will argue that “speciation”, as a process or collection of independent but interacting processes sometimes serving to form genotypic and/or phenotypic clusters, can be studied effectively without any definition of “species” or any requirement that all prokaryotic lineages match such a definition. This has always been so, but formal acknowledgement would have a freeing effect

Philosophy, who needs it? Philosophy of Biology Peter Godfrey-Smith (Princeton University Press, Princeton, New Jersey; 2013) ISBN: 9780691140018

Unknow

Archaea

SummaryA headline on the front page of the New York Times for November 3, 1977, read “Scientists Discover a Way of Life That Predates Higher Organisms”. The accompanying article described a spectacular claim by Carl Woese and George Fox to have discovered a third form of life, a new ‘domain’ that we now call Archaea. It’s not that these microbes were unknown before, nor was it the case that their peculiarities had gone completely unnoticed. Indeed, Ralph Wolfe, in the same department at the University of Illinois as Woese, had already discovered how it was that methanogens (uniquely on the planet) make methane, and the bizarre adaptations that allow extremely halophilic archaea (then called halobacteria) and thermoacidophiles to live in the extreme environments where they do were already under investigation in many labs. But what Woese and Fox had found was that these organisms were related to each other not just in their ‘extremophily’ but also phylogenetically. And, most surprisingly, they were only remotely related to the rest of the prokaryotes, which we now call the domain Bacteria (Figure 1)

Eukaryotes first: how could that be?

In the half century since the formulation of the prokaryote : eukaryote dichotomy, many authors have proposed that the former evolved from something resembling the latter, in defiance of common (and possibly common sense) views. In such ‘eukaryotes first’ (EF) scenarios, the last universal common ancestor is imagined to have possessed significantly many of the complex characteristics of contemporary eukaryotes, as relics of an earlier ‘progenotic’ period or RNAworld. Bacteria and Archaea thus must have lost these complex features secondarily, through ‘streamlining’. If the canonical three-domain tree in which Archaea and Eukarya are sisters is accepted, EF entails that Bacteria and Archaea are convergently prokaryotic.We ask what this means and how it might be tested