Whether you’re whipping up an omelet or baking a batch of cookies, one of the great joys of childhood cooking is the cracking of the eggs. Every once in a while, however, Mother Nature has a surprise up her sleeve — or in this case — hidden inside a shell.

Whether you prefer yours scrambled, hard-boiled or baked in a chocolate cake, take your little one for a journey down on the farm to do some egg-sploring and crack one of the great mysteries of the egg.

Known by some as “the food with a heart of gold,” the egg received its nickname thanks to its sunny, golden center — the yolk! What eggsactly is a yolk, you may wonder?

In a fertilized egg the yolk provides a source of food for the developing embryo. As the chick matures, it pulls nutrients from the yolk until it is strong enough to break through and join its peeps on the farm.

Have you and your child ever cracked open an egg to find two golden yolks snuggled inside the same shell? A common misconception is that a double-yolk comes from a “twin egg.” It may be possible for a fertilized double-yolk egg to produce twin chicks, but the eggs we purchase at the grocery store are not fertilized.

While there are some breeds of hens capable of producing double yolks, most double-yolked eggs we discover inside the cartons on our refrigerator shelves are simply biological practice swings. The majority of these double-yolk eggs are produced when a hen is still quite young and her body is adapting to egg laying.

Once in a while, hens may even produce an egg with no yolk at all. These rare eggs are known as “wind eggs” and usually occur during a hen’s first egg-laying effort.


19 Join the Discussion

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  1. Yep – I have 5 (had six but a hawk got one). Its really easy – give ‘em a place to sleep that predators can’t invade and just keep them fed and watered and “presto” you get eggs! Funny thing is they all tend to want to lay in the same place even if you give them a little space each. You’ll need to clean out their coop occasionally and you can use the poop for fertilizer :) They make a little noise when they are laying (I would too) but nothing too bad.

  2. We purchased one dozen local eggs this summer that contained 5 double-yolk eggs. When you try the eggs from happy, local, free range chickens, you’ll never look at those bland, white, factory produced eggs the same again. There’s a real difference. Better for us, better for your local economy, better for the chickens, and more interesting too!

    • Wow! FIVE double yolks in the same dozen eggs? That’s amazing! Thanks for sharing your “egg”citing discovery, GreenMom!

    • We’re REALLY glad to hear that you enjoyed exploring this Wonder of the Day®, Wonder Girl! YOU ROCK for letting us know! :-)

  3. This wonder was posted a while ago. I am looking today. It is Febuary 11, 2013 and the wonders are in the 800’s. Still, this wonder caught my attention and it’s interesting. P.S. What is the first wonder, I really want to see.

  4. Wow! It seems like you just bit both sides of the egg, but kept a little white in the middle while keeping the egg yolk in the socket. But who knows, I might be wrong.

  5. My brother in law and my sister say the reason a chicken lays a double yolked egg is because the hen has been frightened(?) Is this true? It sounds preposterous to me. Am I gullible or is this true? I’m a surgical nurse of 35 years and this sounds a little ridiculous to me.

    • Hi Janice! Thanks for WONDERing with us! That could be a theory behind the double yolk egg! One reason is usually when the hen is young and still getting used to laying eggs. Also fertilized eggs have an effect as well! Keep WONDERing! :)

  6. Dear Wonderopolis,
    I learned that the eggs we buy at the store are not fertilized! I also learned that the egg is also called “The food with a heart of gold.” The third thing I learned is that some eggs have no yolk and some have two. I wonder how the eggs get formed. Do you know? I also wonder how far up an egg has to be to fall and crack open.

    • Hi Logan! Thanks for WONDERing with us! Wowza, what WONDERful thoughts about eggs and things you’ve learned! The egg is formed from the chicken! We bet the egg doesn’t have to be that high up to crack! They have pretty thin shells! Have you ever cracked an egg? Keep WONDERing! :)

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Have you ever wondered…

  • What is an egg yolk for?
  • What causes an egg to have two yolks?
  • Do eggs always have a yolk?

Wonder Gallery

Try It Out

Eggs are not only an affordable food that can be prepared in a variety of ways, they are also great source of protein, vitamins — and fun! Many families around the country are now raising their own “backyard chickens” (sometimes called “urban chickens.”)

Urban farming is a great way to immerse your child in a rewarding hobby while providing a sustainable source of eggs for your family. You can learn more about urban farming and backyard chickens at backyardchickens.com.

Not quite ready to bring a new feathered friend into your family, but still looking for a way to get your child eggcited about eggs? Why not invite a Pegguin or Pegg to dinner?

Try turning snack time into a nutritious hands-on eggsperience. All you need are a few hard-boiled eggs, toothpicks, sliced veggies and a dash of imagination. Check out the Eggimals website for some inspiration.


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Wonder What’s Next?

Double yolks are quite a pair, but tomorrow Wonderopolis will be cooking up a math lesson that is as delicious as it is smart. Make sure to stop by — and bring your appetite for learning!

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