What leeches and ligers can teach you about evolution
by Maggie Koerth-Baker
If you aren’t totally clear on what constitutes a species, or how scientists draw the line between one species and another, don’t feel bad.
Quite frankly, the scientists are a little shaky on this stuff, as well.
That’s because species aren’t easily defined, and there’s a lot of debate over whether an individual animal, plant, fungus, or bacterium belongs in one species group or another. In fact, if you want to know what a species is, it’s best to not bother trying to grope for a strict definition, taxonomists told me. Instead, every species is really a hypothesis. “It’s a testable conjecture,” said Mark Siddall, curator of the phylums Annelida and Protozoa at the American Museum of Natural History. “It’s a hypothesis about common ancestry, and the recency of that common ancestry.”
But that hasn’t always been the case.
A lot of the language we use to talk about taxonomy today was handed down from the work of 18th-century European scientists. These men, including Carl Linneaus (who is called the father of taxonomy), were working off of a very different understanding of the world. To them, taxonomy was mostly about organizing the natural world that had been given to humanity, in its current form, by God…