Fred,
Do you know of any documentation of a genetic link for kohanim and the ability split their fingers? I'm a kind of skeptical about it.
While genetics might be involved in the ability to split your fingers this is definitely not exclusive to cohanim. I am a yisrael and can split my fingers but remember a teacher of mine who was a Cohen saying that as a child he had to practice spreading his fingers by wedging a plastic cup between his fingers, so it didn't seem to come easy to him despite his cohanic genes.