The biological taxonomy of the common chicken is Gallus gallus domesticus. In other words, this would mean that any "breed" of chicken, whether it's a leghorn or a silkie or whatever, is exactly the same genus, species and subspecies as any other. So, a "breed" of chicken, then, is nothing more than a group of Gallus gallus domesticus that displays a certain homogenous physical appearance and has a set of homogenous characteristics that go along with that homogenous appearance. Supposedly, all common chickens descended from and are a subspecies of the red junglefowl (Gallus gallus) and the different "breeds" have been achieved over the last 6000 or 8000 years of domestication through selective breeding to single out specific physical and/or behavioral characteristics, much in the same way as all of the different breeds of dogs make up a single subspecies (Canis lupus familiaris) of their common ancestor, Canis lupus. OK....so what then is a "hybrid" chicken? I have seen some websites claim that a "hybrid" chicken is nothing more than a cross between two "breeds"? But two different "breeds" of chickens still belong to the very same subspecies. And a hybrid, at least from a biological taxonomy perspective, is an offspring resulting from the cross between two different species of animals. Now maybe lay chicken taxonomy is different than biological taxonomy and these websites are correct, and I'm OK with that.....but, the way we continue to make more "breeds" is by crossing existing "breeds", so why would we ever refer to any crosses at all as hybrids? With this type of taxonomical system, how would one ever truly distinguish a "breed" from a "hybrid" in the chicken world? I would expect that the results of any cross between two different "breeds" which didn't exhibit any obvious common set of homogenous characteristics would simply be referred to as a "mixed breed" or something equivalent to the "mutt" in the dog breeder's world. The reason I'm curious about this is because I have read that some chicken "breeds" have better fertility rates than others. Inbreeding can surely explain this, but if the same good husbandry standards and practices have been used for the development of all "breeds" to keep inbreeding to a minimum, one would think that all "breeds" would have about the same fertility rate (unless, of course, infertility is simply a homogenous genetic characteristic that runs parallel to certain homogenous physical appearance characteristics, and this is certainly possible). But, assuming the former to be true, then true hybridization (the crossing of two similar but different species) present in the history of some "breeds" could account for infertility rates to be different between different "breeds". To confuse matters worse, some people believe that Gallus gallus domesticus, the common chicken, is an ancient hybrid cross between red junglefowl (Gallus gallus) and gray junglefowl (Gallus sonneratii). This would mean that all common chickens, regardless of "breed", would be true hybrids. But, whether or not there was hybridization between G. gallus and G. sonneratii early on in the development of Gallus gallus domesticus, is it possible that the development of more recent "breeds" (say, within the last 1000 years) are the result of some hybridization between Gallus gallus domesticus and another species within the genus Gallus? If so, this would mean that some "breeds" are not Gallus gallus domesticus and some are. Any thoughts on any of this? This is a subject that, as an unschooled backyard biologist/zoologist (I'm a degreed technologist with a passion for natural sciences), is of great interest to me.