Field of Science

What a species is

From now on I'm going to be close to requiring anyone I discuss the concept(s) of species with to have read John Wilkins' post on the subject, How many species concepts are there? Very clear and lucid, really.
What to think? My solution is this:

There is one species concept (and it refers to real species).

There are two explanations of why real species are species (see my microbial paper, 2007): ecological adaptation and reproductive reach.

There are seven distinct definitions of “species”, and 27 variations and mixtures.

And there are n+1 definitions of “species” in a room of n biologists.
I don't mean to say that Wilkins get the final word, but just that his categorizations is most germane to the topic. I, for one, (also) think that Ernst Mayr committed several blunders when emphasizing the Biological Species Concept. And the name itself was one of them. I'm the lone evolutionary biologist in a microbial lab a the moment, and we don't like not talking about different species of bacteria, for example. Sex is great, but not always for everybody.


  1. There are seven distinct definitions of “species”, and 27 variations and mixtures.

    Or, to put it another way: Definitions of "species" are divided into seven distinct genuses, which are further divided into 27 species of "species"?

    Oh noes it's a taxonomy of taxonomies!

  2. Should have noted that myself.

    Also, it's genera, so no degree for you.

  3. Drat. I was pretty sure there was an irregular plural for "genus" but I was too lazy to look it up.

    On a serious note, I really need to take some time and carefully read Wilkins' post. The species concept as it relates to asexual organisms has always troubled me. For sexually-reproducing species, even though you would never do so in practice, it would be possible in principle to create a reasonable yes/no metric for whether two organisms were members of the same species (e.g. set a specific threshold for probability of producing reproductively viable offspring given a particular degree of geographical overlap, extended out over a certain number of generations or something -- never mind the practical impossibility of using such a criterion, my point is that you could define it in principle). But with asexual species, I wouldn't even know where to start.

  4. I'm writing a paper where I use the ecological species concept (Van Vaen, 1976) to define asexual species: ``a lineage which occupies an adaptive zone minimally different from that of any other lineage in its range and which evolves separately from all other lineages outside its range." I have no space in my model, so it ends up being that two subpopulations are different species if they can coexist at zero mutation rate (they do this by using different resources, which results in frequency-dependent selection).


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