Assuming the FCS is neutral in bats (which I don't think we could prove or disprove without more sampling, but which I agree is possible), I agree that the muta

Assuming the FCS is neutral in bats (which I don't think we could prove or disprove without more sampling, but which I agree is possible), I agree that the mutation wouldn't have to happen concurrently with the species jump. Even if the FCS is negative in bats, it's also possible that the FCS evolved naturally in a different animal host. I agree there's no evidence to exclude those scenarios; I just don't see any specific evidence to favor them either.