Why be shaped like a snake? (Also, weasels)

Here’s a puzzle: you’ve gone to all the bother to evolve fins, then limbs, and then even limbs with all these complicated joints and toes and whatnot—and then you lose them. Limbs all gone.

You're just a head and a tail now. Why, corn snake, why?

You’re just a head and a tail now. Why, corn snake, why?

This seems counterproductive, to say the least. Yet it isn’t just the snakes going in for the serpentine body plan: caecilians, amphisbaenians, and legless lizards lost their legs, too, and they aren’t evolved from snakes—these limbless animals all lost their limbs independently.

To understand how being snake-shaped might be adaptive, we’ll also consider some animals that are almost—but not exactly—snake-shaped: the mustelids, or weasels.

Least weasel. Photo by Sergey Yeliseev*

Least weasel. Photo by Sergey Yeliseev*

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Think like a scientist: sample size

Science is not just for scientists. The methods of thought that underlie science are useful in all sorts of everyday contexts. Most obviously, everyone needs to be able to think like a scientist in order to interpret scientific results—you know, those newspaper headlines like “PAPER CLIP USE MAY LOWER IQ IN PREGNANT WOMEN!!” In that spirit, I’m going to write about some key concepts for thinking like a scientist. Today: sample size.

Pop quiz! You read this (totally made up) report: “Two groups of ten age- and health-matched men were monitored for heart disease. One group was given pet ferrets, while the other was not. The ferret-owning men were 8% less likely to develop heart disease over a five year period.” So: is it time to run out and get a ferret for the sake of your heart health?

You should get a ferret regardless, because ferrets are wonderful. This is my awesome old ferret Zap.

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