At work last Monday, I came by this as I was making muffins:
Now, I've cracked a lot of eggs in my life - a lot of eggs - but I've never come across a double yolk before. It got me wondering how unique they are, and I came up with this bit of information to wow you all with.1. Double yolks are a "mistake" in the chicken's reproductive system that sometimes happens when a hen just starts laying eggs and her system is still trying to figure out how to do it correctly. It may also be hereditary. [source]
2. Double Yolkers appear when ovulation occurs too rapidly, or when one yolk somehow gets "lost" and is joined by the next yolk. Double yolkers may be by a pullet whose productive cycle is not yet well synchronized. They're occasionally laid by a heavy-breed hen, often as an inherited trait. [source]
3. Most double yolk eggs are produced by young birds, so therefore barns that contain young flocks have a large concentration of these eggs. Usually a young bird will lay a small egg, but if the egg is a double yolk, it tends to be either large or extra large size. This tends to be true in humans as well, where expectant mothers tend to become “larger” for multiple birth pregnancies. [source]
4. Usually a double-yolked egg will be longer and thinner than an ordinary single-yolk egg. Double-yolked eggs occur rarely, only leading to observed successful hatchings under human intervention, as the unborn chickens would otherwise fight each other and die. [source]
