Non-Christians would presumably reject outright that God has worked in human history, so my argument from analogy would be meaningless to them. But I would hope your Christian colleagues would give it a fair hearing and consider it. If it is not a macro-evolutionary event, then PC has no argument with it. The amount is to be determined by the geological record and biological experimentation. But there is no vertical radiation.
Vertical radiation is only by fiat creation.
A root-species may give rise to several species by horizontal radiation, through the process of the unraveling of gene potentialities or recombination. Horizontal radiation could account for much which now passes as evidence for the theory of evolution. The gaps in the geological record are gaps because vertical progress takes place only by creation. Oh, there are the Kenyons, Gishes, and Morrises . . . Yes, and thank you to you.