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I think this strict interpretation is necessary when debating very literal minded creationists who would simply argue that even though organisms A & B don't reproduce in nature, the still COULD reproduce and thus aren't really seperate species.
I will very politely disagree. What needs to be conveyed to creationists is that speciation is a matter of genetics. If two new populations do not mingle DNA, then different mutations will accrue in each population. Over time, this will lead to greater morphological differences and eventually to a physical barrier that prevents interbreeding. Evolution requires that, for biodiversity to appear, there has to be a process that separates genomes. Speciation is that method.