Elder offspring: Do you know why eggs are egg-shaped?
Younger offspring: Because they’re eggs?
Dr. Free-Ride: Indeed, it would probably be surprising if eggs, of all things, weren’t egg-shaped.
Elder offspring: (sighing) What I meant was, do you know why eggs have the particular oval shape that they do, narrower at the top and wider at the bottom?
Younger offspring: Hmm. I think it has to do with the shape of the chicks. Chicks are wider at the bottom than at the top, and they need to fit in eggs to be laid by the chickens, so that’s why eggs need to be that shape.
Dr. Free-Ride: That’s a very interesting explanation. I’m guessing, though, that your sibling has another explanation in mind.
Elder offspring: Yes.
Younger offspring: But why do you think they’re egg-shaped.
Dr. Free-Ride: I have a guess, but I want to wait to see what [Elder offspring]’s explanation is.
Elder offspring: Well, it’s not just chicken eggs that are egg-shaped. Many, many other birds lay eggs that are oval rather than round, and reptiles, too, I think.
Younger offspring: That means I’m wrong about why eggs are egg-shaped.
Dr. Free-Ride:Why is that?
Younger offspring: Alligators come from eggs, and baby alligators aren’t egg-shaped like baby chickens are.
Dr. Free-Ride: Still, it wasn’t a bad guess.
Elder offspring: The shape does have to do with the young in the eggs, though, kind of.
Younger offspring: How?
Elder offspring: Eggs are oval instead of round so they don’t roll out of the nest and break. The eggs of birds that build their nests on high cliffs are the least round, because they’d be in the most trouble if they rolled out. The eggs of creatures that nest on the ground are closer to round, because they don’t have very far to fall.
Dr. Free-Ride: That’s cool. And since you’re explaining it so authoritatively, I’m guessing that you read this in some credible source.
Elder offspring: Uh huh. It was in a Zoobooks I borrowed from the library.
Younger offspring: Can I read it next?
Elder offspring: Sure. What was your idea about why eggs are egg-shaped?
Dr. Free-Ride: It had to do with what would make it easier for the mama critter to lay the eggs.
Elder offspring: Hmm. I hadn’t even thought of that.
Dr. Free-Ride: Sometimes, when you’re a mama critter, it’s hard not to think of things like that.