I've been talking to a friend and an old professor, both of whom hold PHD's about the curiosity of charcoal hens being sterile. Both of them agreed that the most likely explanation is that they have a defective gene on the female chromosome that doesn't "turn on" like its supposed to. Males get one male chromosome and one female chromosome so they remain fertile because they have at least one functioning copy of the sex chromosome whereas if the female's have a defective gene on them then they have no backup. It also doesn't help that charcoals are egregiously inbred and most of them show visible signs of inbreeding depression even at a young age. I've seen a few people claim that their Spalding charcoal hens have laid but hybrid vigor does not replace defective sex genes. I'm sure were I to post this information on facebook I would get crucified but hopefully on here cooler heads will prevail.
