As a thought experiment, if you imagine ring species in time almost anything can "breed" with almost anything else. Eg each human can breed with a human in the

As a thought experiment, if you imagine ring species in time almost anything can "breed" with almost anything else. Eg each human can breed with a human in the previous generation. Each chimp can breed with a chimp in the previous generation. Right back to their common ancestor. As long as there's a common ancestor, there should be a viable chain to be followed in most cases.