THE ORIGIN OF SPECIOUS:

There are species today that will be two totally distinct animals a hundred years from now. But at what point in the process do they become different enough for us to treat them as such?

A new study by a group of French biologists highlights just how much trouble this question poses. They found what they call a "grey zone" in which different populations of animals are starting to diverge into two separate populations, but aren't yet so distinct that they are obviously different species. Their study, published on Tuesday in PLOS Biology, looked at 61 pairs of populations or species to see how much they were sharing genetic information, and found that the line between distinct groups of animals was pretty fuzzy. When animals diverged genetically by 0.5 to 2 percent, it was hard to tell whether the pairs of animals were one species or two.

That might not seem like it matters. Why should we care about a tiny minority of organisms that are in the process of evolving? Either they'll become separate species, at which point we'll give them different names, or they won't and it'll all be a moot point anyway.

But of course it matters. Because if we can't decide when a species becomes a species, it means we don't have a very useful definition of "species." 

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