Vaccines—Who Needs 'Em?

[rvg]

No, they were two distinct sub-species.

This is why wolves are now classified as canines rather than lupines, because they can successfully interbreed.

But the issue remains. You can't jump to being a different species before being a different sub-species. That's the first step on the road to evolutionary separation. So, who's to say that a normal chicken isn't merely a one-headed protochicken, as opposed to being a new sub-species?

Or to put it another way, we can go all the way back to the first chicken. Its parent had to be a protochicken, otherwise its parent would be classified as the first chicken.