When does microevolution turn into macroevolution?

I appreciate your concerns, Nuggin. But it's not a bad thing at all, not at all, for fundies to witness scientists in discussion. They get to see people who really have taken the trouble to understand these subjects, who sort through evidence and discuss it, who don't repeat one-size-fits-all answers learned by rote. They get to see the basic innocuousness and fundamental honesty of the whole scientific enterprise (such a contrast the reality makes with the picture they've been given of it!). And in the course of the discussion they are introduced to concepts, issues, and unsolved mysteries they didn't even know existed. They get to see what open inquiry and real expertise look like.It's good for them. For some, it will be the first experience of these things.It's okay.

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ArcherAll species are transitional.

Gonna start a new thread

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

You might want to add this paper:de Rosa R, JK Grenier, T Andreeva, CE Cook, A Adoutte, M Akam, SB Carroll and G Balavoine (1999). Hox genes in brachiopods and priapulids and protostome evolution. Nature 399: 772-7776From the abstract:

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Understanding the early evolution of animal body plans requires knowledge both of metazoan phylogeny and of the genetic and developmental changes involved in the emergence of particular forms. Recent 18S ribosomal RNA phylogenies suggest a three-branched tree for the Bilateria comprising the deuterostomes and two great protostome clades, the lophotrochozoans1 and ecdysozoans2. Here, we show that the complement of Hox genes in critical protostome phyla reflects these phylogenetic relationships and reveals the early evolution of developmental regulatory potential in bilaterians. We have identified Hox genes that are shared by subsets of protostome phyla. These include a diverged pair of posterior (Abdominal-B -like) genes in both a brachiopod and a polychaete annelid, which supports the lophotrochozoan assemblage, and a distinct posterior Hox gene shared by a priapulid, a nematode and the arthropods, which supports the ecdysozoan clade. The ancestors of each of these two major protostome lineages had a minimum of eight to ten Hox genes. The major period of Hox gene expansion and diversification thus occurred before the radiation of each of the three great bilaterian clades.

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A

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Natural Selection is not Evolution-- R.A. Fisher

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

Something can be both rapid and gradual. They are not mutually exclusive terms. If something happens in grades in a relatively short period of time, it is still gradual.

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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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Relatively few changes in Hox genes can have large phenotypic effects.

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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?

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I don't think you can assume it happened in just a few generations. Up to 1/3 of new mutations--regardless of selective value-- are lost to drift straight away. Those that do make it then have to become fixed in the population, which can take many generations, depending on selective value and population size.AEdited by Allopatrik, : No reason given.

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Natural Selection is not Evolution-- R.A. Fisher