Maybe you’ve heard this one:
How many legs does a spider have? Eight? Do you really know? I mean have you counted them? In 300 B.C. Aristotle said that spiders had six legs and was classified as an insect. All the world believed him, until finally in the 1400s somebody actually counted and saw they had not six, but eight legs. Aristotle must have been widely respected for no one to question him for 1,700 years. I am sure he was right about a lot of things, but not this time. Finally, somebody counted the legs for themselves instead of just taking Aristotle’s word for it.” —William Earnhardt
Great, right?
Except that—as far as I can tell in a day—Aristotle didn’t claim that spiders had six legs. He did mention spiders quite a bit in his writings on nature. But I couldn’t find anything at all about spider legs, only modern people talking about spider legs and crediting Aristotle for a mistake easy to resolve with observation.
Why didn’t Earnhardt question this story? Perhaps because he’s not alone in telling it. UNESCO’s geologists and evangelists alike have spread this anecdote over the years, and it seems incredibly resistant to correction.1
Twenty-three hundred years ago, Aristotle wrote about some legs: the legs of a particular species of fly. Arachnids aren’t insects, but, like insects, are part of the arthropod family.
How many legs does [Ephemeroptera] have? Well, it is standing on four, because the forelegs are specialised simply to hold onto the female during mating in flight (the sole task of the adult mayfly). Aristotle, who counts legs based on their functionality, is in fact correct, if that is the kind of species he was observing. We say it has six legs because the forelegs are homologous with the hindlegs. He said four because the forelegs aren’t used for walking.” —John S. Wilkins
It’s fascinating how easy it is to lean on short, slick stories that reinforce our ideas about the world or about authorities we’re skeptical of. It’s easy to trust our favorite writers when they pass those stories along, to take the anecdotes for granted because of the function they serve.
But do as Earnhardt says (and not as he does): observe, fact-check, and investigate, even and especially when a story satisfies your assumptions.
There’s no reason to let a good anecdote get between you and the truth.
If you have a direct citation for Aristotle’s writings that would clear up this conundrum for me, please let me know!
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- The article by B. Lukács appears to have been written in a non-English language and later translated.