When does microevolution turn into macroevolution?

To be honest Hoot this basically lies in the realms of the same problem you get when creationists complain that we can't show them a cat giving birth to a dog. There is no reason to assume that the latest common ancestor of the protostomes and deuterostome had a specific modern protostome body plan with an anus and mouth of any particular embryonic origin.In fact many modern protostomes may only have a mouth or only an anus. So the latest common ancestor of both may well have not had a discrete mouth and anus (Neilsen, 1994). There is a similar argument that rather than an inversion of the protostome body plan seen in annelids and arthropods, leading to deuterostomes having a dorsal nerve chord and ventral heart, the differences can be explained by "a common ancestor with diffuse dorsoventral organization, followed by oppositely directed condensation of the nerve cord and relocation of the heart in the two lines" (Gerhart, 2000).TTFN,WK

Could you clarify this? Are you talking about changes in allele frequencies or gross morphological change? I appreciate that the latter necessitates the former, but we may see sweeping genetic change not reflected in radically different morphology.TTFN,WK

Is that a requirement for being a protostome?I'm saying that all modern protostomes are likely to have had a common ancestor which had a blind gut and that some modern protostomes still show this feature. If you want to argue that blind guts are a derived feature or that there are no protostomes which have a blind gut then feel free, but please try and make some sort of argument.*ABE* There is a compelling case to be made, based on gene expression (Arendt, 2001) and other developmental considerations (Erwin and Davidson, 2002), that the most recent common ancestor did have a through gut. But that doesn't make your original contention better, it just means I was wrong about the nature of the most recent common ancestor.TTFN,WKEdited by Wounded King, : No reason given.