Adventures in Ethics and Science

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.


  1. #1 Laelaps
    February 1, 2008

    This one reminded me of Ken Carpenter’s book Eggs, Nests, and Baby Dinosaurs, especially on the topic of how eggs can show a wide array of shapes and constructions.

    It also reminded me of something I had just read from Darwin;

    “Now, if nature had to make the beak of a full-grown pigeon very short for the bird’s own advantage, the process of modification would be very slow, and there would be simultaneously the most rigorous selection of the young birds within the egg, which had the most powerful and hardest beaks, for all with weak beaks would inevitably perish: or, more delicate and more easily broken shells might be selected, the thickness of the shell being known to vary like every other structure.”

  2. #2 Larry Ayers
    February 1, 2008

    Another wonderful sprogalogue! Something I look forward to every week, and I hope you someday compile these exchanges into a book.

  3. #3 Scotty B
    February 1, 2008

    I’ve got a great book at home called Chickens Aren’t The Only Ones that is a great book about the different eggs laid by different animals. I think its by a woman named Ruth Heller?

  4. #4 Uncle Fishy
    February 1, 2008

    Ah, but why are fish eggs round (and in some cases delicious)? You can get right into differential calculus if you play your cards right. Except for the delicious part.

  5. #5 KeithB
    February 1, 2008

    If you ever get down to the Aquarium of the Pacific in Long Beach, CA, they have an exhibit comparing the shape of clif-dwelling birds eggs to regular eggs. They have a tilting table to show how far the eggs can roll. The highly conical cliff-dwelling egg (from a murren?) quickly rolls in a circle and does not go very far.

  6. #6 OmegaMom
    February 1, 2008

    Hah! As a woman, my immediate response was also “so it’s easier to lay the damned things!” But, since the idea of “shaped to not fall” is raised, would this mean that animals that lay eggs in ground-based nests (on flat terrain, as opposed to the cliffdwellers referenced above) would in general tend to have oval/round eggs versus “egg-shaped”?

  7. #7 Alan Kellogg
    February 1, 2008

    One thing to note here is that one animal with (nearly) perfectly round eggs is a mammal, the platypus. :)

  8. #8 Eva
    February 2, 2008

    My absolute favourite part of this exchange is this:

    “That means I’m wrong about why eggs are egg-shaped.”

    Realizing you’re wrong and correcting yourself based on new information is exactly what makes someone a good researcher/thinker/generally-smart-person and many adults can’t even do this!

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