Thread: Species

How do you define a species for asexual animals?

I'd say it depends on similarity in DNA. Am I correct?

*This came up in a debate with a Creationist*

Originally Posted by scientstphilosophertheist

How do you define a species for asexual animals?

I'd say it depends on similarity in DNA. Am I correct?

*This came up in a debate with a Creationist*

In general, yes, though it's important to remember that the designation of "species" is much more of a human organizational idea that it is a concrete natural entity. And cases like asexually reproducing organisms are ones where applying the species label is definitely more difficult.

anyway, as far as multicellular organisms is concerned, asexual reproduction is the exception rather than the rule

...the designation of "species" is much more of a human organizational idea that it is a concrete natural entity...

That's a needlessly careful statement. "Species" is nothing but a human concept, of course, just like all of Linnaeus' taxonomy. It's an attempt to describe a complex reality by simple categories. Any categorization uses generalizations to some extent, and needs to be re-defined when deemed incomplete or inconsistent. How or whether the species concept applies to organisms which exclusively reproduce asexually is simply a question of definition. Categories and their definitions are arbitrary. To re-iterate marnixR's question: Does the "species" concept, by its modern definition, apply to asexually reproducing organisms? If yes, how so (by DNA similarity)?

[quote="M"]

Does the "species" concept, by its modern definition, apply to asexually reproducing organisms? If yes, how so (by DNA similarity)?

I find it doubtful that the modern concept of species can be used for asexually reproducing organisms. Even if DNA similarity were the criterion used there would be an unfortunately arbitrary point at which we decide that there is or isn't 'enough' similarity. Talk of 'lineages' as a substitute (for bacteria, for example) may be slightly better, but is still not great.

Having said which, I think the species notion is still very useful, just one which like Wittgenstein's games, may not be capable of a single unambiguous definition.

Originally Posted by scientstphilosophertheist

How do you define a species for asexual animals?

I'd say it depends on similarity in DNA. Am I correct?

*This came up in a debate with a Creationist*

You could use 'organisms' instead on animals and expand he definition even further.

I worked with a crusty old doctor emeritus when graduating university and first doing paleontology. Throughout my studies everyone praised ad nauseum Linnaeus and his framework for genus and species . So it was refreshing when this seasoned old fellow used to declare that Linnaeus did more to muddle taxonomy than anyone else. Old Doc would rant that Linnaeus created a subjective construct 'the species' and left future generations floundering around using equally subjective taxonomy to build houses of cards around questionable species and pushing too much equivalence of apples and oranges. Binomial taxonomy survived Darwinism but, thankfully, doesn't have the prominence it did a few decades ago. It's becoming more of a 'tool' of organization and recognized as such rather than a 'chart' of life. More functional than descriptive and thus open to change and less revered.

So, as you say, one could say that there is a similarity of DNA when defining a species but a word like 'similarity' is subjective. How similar? More similar than...? most biological disciplines govern themselves. 'Species' as a definition is less important than consistency within the discipline. Entymologists who study flies (diptera) usually don't study ants or butterflies. A taxonomy of flies isn't necessarily the same equivalency as one on butterflies. The species definition might be broader or more restrained and so are each of the uses of genus, family and order. The 'species' level is more of a tool for study rather than an absolute as it was treated before Darwinism and especially before knowledge of genetics based on DNA.