how do some chickens make a majority of “double yolk”?

Question

I had a carton of eggs, so far 5/12 have contained a double yolk (there are 3 left) this seems well beyond the estimates for young/old chickens online and by their math, astronomically unlikely.

Are there reasons this may happen related to the chicken?

In: 7

Answer 1

Older hens’s eggs are more likely to have double yolks. Some supermarkets select for those and sell them:

https://www.thegrocer.co.uk/new-product-development/mands-to-sell-boxes-of-guaranteed-double-yolk-eggs/513367.article