When does microevolution turn into macroevolution?

TD wrote: Yes, that's one POV. But another is that macroevolution must have been highly punctuated. Some macroevolutionary events could NOT have been gradual, such as the separation of deuterostome from protostome branches in the animal kingdom. If macroevolution entailed mutated Hox genes, for example, it could have happened in a geological instant. On the other hand, the evolution of reptiles to birds was apparently not instantaneous, according to fossil records. Some biologists have said that birds are just different kinds of reptiles with feathers instead of scales, and that no macroevolution was ever involved”only speciation. And then the trouble ensures over whether or not speciation IS macroevolution. Even celebrated Harvard biologists do not agree precisely on the difference between macroevolution and microevolution and where speciation fits in.”HM

Mod says: Please explain to me how the deuterostomes separated from the prototomes gradually. That macroevolutionary event involved an either-or situation. The blastopor on an animal's embryo can become either the mouth or the anus of the developing organism, not both. You know, Mod, even fertilization can be seen as a gradual event. What are your temporal criteria that legimitize gradualism and dispatch punctuated equilibrium theory?”HMEdited by Hoot Mon, : No reason given.

Mod, I take notice that Gould (in Ontogeny and Phylogeny, 1977) defines "macroevolution" this way:

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The study of evolutionary events and processes that require long times for their occurrence or operation”conventionally defined at taxonomic levels involving the origin and development of species and higher taxa, not changes of gene frequencies within local populations.

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He gives your side of our argument a lot of support. So that's one for you.But I still don't know why ALL evolutionary events must be necessarily gradual. I still think some very big events could have been quite sudden. There are good arguments, for example, that larval stages may have served as radical points of departure in certain evolutionary bursts. And it is well known that small changes in the Hox genes of an organism can produce huge changes in its deveopment”some heritable.E. O. Wilson (in Sociobiology, 2000) defines "macroevolution" only as a default term for "evolution," both of which he enfolds into his definition of "microevolution":

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A small amount of evolutionary change, consisting of minor alterations in gene proportions, chromosome structure, or chromosome numbers. (A large amount of change would be referred to as macroevolution or simply as evolution.)

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Ernst Mayr (in What Evolution Is, 2001) defines "macroevolution" as:

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Evolution above the species level; the evolution of higher taxa and the production of evolutionary novelties, such as new structures...Microevolution [is] evolution at or below the species level.

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So the Harvard heavies may be more on your side than on mine. But I'm holding firm for a while with my assertion that very big evolutionary changes can ocur in a geological blink”maybe requiring only a few generations.”HM

Nuggin wrote: OK. Biological evolution is an indisputable scientific fact. However, the mechanics and processes of biological evolution are not yet fully understood or agreed upon, which by no means disqualifies biological evolution itself as a scientific fact.”HM

But do all the Fundies agree on what "God's eternnal love" means? On what "free will" means? On what Jesus's "resurrection" means? I have no idea what they mean, but I'll bet they are regarded as crucial conecpts ("truths") in your religion. So who's a "Fundy"? Does the Pope walk in lock step Jerry Falwell? Which Fundy is more Fundy than another Fundy?”HM

Observation: As embrogenesis progresses in animals with complete digestive tracts, the embryo forms around a hollow cavity, the "blastocoel," and it produces a" vegetal plate" where an opening, a tiny hole, develops. This hole is called the "blastopore." In "protostomes" animals (nematodes, arthropods, annelids, mollusks, et al.) the blastopore eventually becomes the animal's mouth. In "deuterostomes" animals (echinoderms, hemichordates, and cordates) the blastopore becomes the animal's anus. Questions:How could any protostomes animal population evolve gradually into a deuterostomes animal population? How could a blastopore gradually evolve from generating an animal's mouth to generating its anus?Why wouldn't that be a case for very sharply punctuated equilibrium, since there are no in-betweens?”HM

WK wrote: How do they manage to do that if they have complete digestive tracts? Are you saying that these "modern protostomes" have devolved back into mesozoans?”HM

WK asked in Message 41: Only to say this again about embryology: That radical switch from the blastophor morphing into the organism's mouth over to the blastophore morphing into its anus does not look like it could have been gradual to me (perhaps in the same sense that a woman does not become gradually pregnant).Moving on: These are relevant references. Thanks.Arendt, et al.:

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Evolution of the bilaterian larval foregut

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Bilateria are subdivided into Protostomia and Deuterostomia. Indirect development through primary, ciliary larvae occurs in both of these branches; however, the closing blastopore develops into mouth and anus in Protostomia and into anus only in Deuterostomia. Because of this important difference in larval gut ontogeny, the tube-shaped guts in protostome and deuterostome primary larvae are thought to have evolved independently. To test this hypothesis, we have analysed the expression of brachyury, otx and goosecoid homologues in the polychaete Platynereis dumerilii, which develops by means of a trochophora larva”the primary, ciliary larva prototypic for Protostomia. Here we show that brachyury expression in the ventral portion of the developing foregut in Platynereis and also otx expression along ciliated bands in the mouth region of the trochophora larva parallels expression in primary larvae in Deuterostomia.

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And Erwin et al.:

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The last common bilaterian ancestor

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Many regulatory genes appear to be utilized in at least superficially similar ways in the development of particular body parts in Drosophila and in chordates. These similarities have been widely interpreted as functional homologies, producing the conventional view of the last common protostome-deuterostome ancestor (PDA) as a complex organism that possessed some of the same body parts as modern bilaterians. Here we discuss an alternative view, in which the last common PDA had a less complex body plan than is frequently conceived. This reconstruction alters expectations for Neoproterozoic fossil remains that could illustrate the pathways of bilaterian evolution.

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Evolution that occurred in embryonic and larval stages could have been radical and abrupt. Heritable traits from those events could amounted to macroevolution over very few generations. At least that's the way I see it.”HM

Allopatrik suggests: Yes, very relevant. I suspect that evolution at the level of Hox genes and larval development must have involved some radical departures. Some of those changes involved very few genes:

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...The ancestors of each of these two major protostome lineages had a minimum of eight to ten Hox genes...

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So I want to assume that such macroevolution, if that was what it was, happened rapidly. Am I wrong in doing so?”HM