Evolution, religion, and ignorance.

[Angrboda]

I would have to disagree with the supposition that once you've demonstrated microevolution you've thereby demonstrated macroevolution because macroevolution is "just more of the same." That's an unscientific assumption that a trend will, left to its own devices, continue in the same direction and at the same pace. This isn't a valid assumption in the general case, and it's not valid as an assumption in this case. We don't know enough about the mechanics of genetics to say that there are no limits to variability at the biological level "based solely on observation of microevolution in existing genetic populations." The conclusion that macroevolution occurs is one based on a pattern of evidence, it's an inference from a lot of evidence. In that respect, it is categorically different from microevolution. We can see microevolution and demonstrate it in the lab. The same can't be said for macroevolution; it must be inferred from a pattern of evidences. Thus I think there is a real barrier to both the demonstration of macroevolution, and the acceptance of it, which doesn't exist with microevolution. Both can be demonstrated to occur, yet the demonstration of macroevolution is categorically different from the demonstration of microevolution, and with that difference enters the possibility of doubt of the former, while simultaneously accepting the latter. This is not just pigheaded refusal to accept that microevolution and macroevolution as being the same; it's an acknowledgement that the evidence for one and the evidence for the other are unique. One can withhold assent for macroevolution without being inconsistent in one's acceptance of microevolution, and I don't think the burden is necessarily on the skeptic of macroevolution. If the evolution advocate's position is simply assuming that the trend of microevolution can extend beyond the boundaries of species, then he or she needs to demonstrate it with more than an assumption of uniformity of trend.