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Evolution for Third-Graders
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Red Crayfish (Procambarus clarkii) by Pam Corey, via Flickr CC BY-NC-ND 2.0.

It’s early on a Friday morning, and I’m standing in front of a crowd of eight-year-olds holding a fistful of dead crayfish. The mudbugs are a biological supply company purchase sorted into sealed sandwich bags – the subject and substrate for the science project I’ve volunteered to lead today.

The activity I’ve planned is the most basic sort of comparative anatomy: we’re going to dissect crayfish and talk about how their bodies differ from our own. These kids won’t learn about evolution in school for years yet, but I’m hoping to lay some groundwork now that will make it a little less alien when they finally do get to it.

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Before we start, I ask if they can think of any other animals that are related to the crayfish. Hands shoot up. Lobsters, crabs, ants and other insects are named. I add a few other arthropods to the list, then drop the bombshell that makes them really pay attention: biologists think that every one of them is also a very very very distant cousin to those crayfish, the relative we shared probably looked a lot like a worm, and over the next hour I want them to think about how both the crayfish and vertebrates like us have solved the same problems while becoming less wormlike. They put on their gloves, I give them some quick instructions on how to use their dissecting scissors and probes, and at last, I hand out the specimens.

There’s a chorus of ‘eeew’s as the kids dump crayfish onto their dissecting trays and the faint smell of preservative fluid wafts out of the bags. It’s followed by 40 minutes of barely controlled chaos.

We count crayfish legs. We look at the eyes and the antennae. We look for the mouth, and talk about what all the little leg-like structures that surround it are for. We figure out whether each group has a boy crayfish or a girl crayfish. We cut open the thorax and look for gills, heart, and stomach. We open the stomach and poke the hard gastric teeth with our fingers. (The kids are delighted by the very idea of “stomach teeth.”) We find the nerve cord running along the belly and the intestine running along the back of the animal – the exact opposite of our own body plan. Some kids ask what’s inside the eyes. Others ask where the crayfish keeps its brain. I try to find something recognizable to point out inside the specimen that one group has poked to paste. At one table, a dark-haired girl has pushed her body as far away from the crayfish as possible, face twisted in disgust, but still cranes her neck around to see what her partners are doing. At another, a girl and a boy keep repeating to one another, “This is the best day ever!”

After we clean up, the kids ask questions – but very few of them are actually about the dissection. Most of them, it turns out, are about me. What other animals have I dissected? What’s the worst thing I ever smelled? How long does it take to get a Ph.D.? What do I do at work all day? Do I have a dog?

I get it, really. I’m probably the first scientist they’ve met in the flesh. All those questions are just proxies to ask: “If I wanted to, could I be a scientist when I grow up, too?” Hopefully, I was able to let them know that even though it takes a lot of hard work, the answer to that question could be yes.

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