In The Language of Science and Faith, (IVP Books, 2011) explaining how microevolution can become macroevolution, they explain,
If a population of some species undergoes a substantial number of such changes [genetic mutations], it can eventually turn into a new species, a process called speciation. Usually speciation requires that the population be geographically isolated from other related populations so that the beneficial genes do not get diluted among the entire population. Mutations in the human species, for example, can easily spread among the entire population. But if everyone from, say, Canada, moved to the moon, then mutations in that population could eventually, over millions of yeas, lead to a new species that would be unable to breed with the parent species on earth. The new species would not necessarily be more advanced in any meaningful sense; it might even be less advanced according to some criteria. But it would be different.
Some sources don’t find this example a slam dunk. Thoughts? Note: It may already have happened.