What Are The Odds Of Finding A Bonus Yolk In Your Eggs?

You wake up one morning and decide that you want some eggs and toast for breakfast. You put the bread in the toaster, warm up the skillet, and grab one or two eggs from the carton. All of it seems to be another mundane breakfast routine until — hold on a moment, you only cracked one egg into the pan, right? Why are there two egg yolks floating around, then? It must be your lucky day, getting two yolks out of one egg.

To understand the mystery of just what exactly this "double yolk" or "bonus yolk" is, we have to first understand what an egg yolk is. Egg yolks are something of a built-in food source for any developing chicks within the shell, containing enough vitamins and minerals for the embryo and later chick fetus to feed on while it develops. If you were ever to notice a very tiny white spot on the surface of your yolk, it's very likely you're looking at the egg cell of a developing chick. You needn't feel guilty about "eating" a baby chick, however, as most of the eggs we purchase from the supermarket aren't fertilized, meaning there's been no development of chicks or even egg cells at all.

But if a single egg yolk is meant to serve as a natural food source for a developing chick, what do two yolks imply? Is it an uncommon but natural sight or is it a sign of some kind of "deficiency" with the egg? 

While we may not be able to say that we understand what a chicken is thinking and feeling as it's laying an egg, we can tell you that it's admittedly unusual to find an egg that has two yolks instead of one. What causes this to happen?

Double-yolked eggs may be more common in the eggs of younger chickens or chickens that have just started to lay eggs. Unlike older chickens, the reproductive systems of these hens aren't fully matured, meaning that certain eggs can be either misshapen, smaller, or in some cases, have two yolks.  The hen's ovulation cycle, which provides the yolks during the formation of the eggs, may "slip up" and give an extra yolk. Over time, as the hen matures into adulthood, their reproductive system matures and begins to lay eggs at a natural rate. As the eggs of adult hens are the ones most often found in supermarket egg cartons, the chances of finding a double-yolked egg are incredibly uncommon. In fact, only one in 1,000 eggs have a chance to contain a double-yolked egg, meaning you'll need to crack a lot of eggs if you want to get your "bonus yolk."

Aside from looking unusual and being something to post on social media, a double-yolked egg is as safe to eat as any other egg. Your scrambled or fried eggs may take on a brighter color, but they'll still be as delicious as ever. 

If you cracked an egg into your pan and found that you have two whole yolks, you may think of one thing: twins. It's not unreasonable to think that, considering that the yolk is a food supply for an embryo. Wouldn't it make sense for an egg with two yolks, then, to be a sign that this egg would have had twin chicks?

Incubating a fertilized egg that has a double yolk (should you know it has a double yolk) is possible, but one shouldn't get their hopes up to see twin baby chicks. One embryo may "outlast" the other embryo, meaning that only one chicken will hatch in most cases. In other cases, you may get twin chicks, but one chicken will be weaker and smaller than the other. While it's entirely possible both chickens can hatch and survive, it's usually a case of one chicken being born or none being born at all.

Some cultures, however, interpret the double yolk as a symbol of things to come. Chinese culture, for example, believes that the appearance of two bright golden egg yolks inside one eggshell is a sign of prosperity and good fortune to come while the Norsemen believed two yolks to be an omen of death to someone close to you. Some may even interpret the double yolks as a herald of an expecting pregnancy– perhaps with twins. Egg yolks are not only a good breakfast, but a fortune teller as well.