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ORIGINAL: unclemonkey

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In that case you have no basis for the assertion that the finches have not speciated.

When did I make that assertion?

Jack. I made the statement that claiming a finch “evolving” into a finch is empirical evidence that a lizard can evolve into a mammal is a “bait and switch” con game. Since you haven’t said anything about finches that must be the source of glaudys’ assertion. It’s ironic that you and I are constantly accused of distorting gluadys’ words.

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ORIGINAL: Jhud

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Jack. I made the statement that claiming a finch “evolving” into a finch is empirical evidence that a lizard can evolve into a mammal is a “bait and switch” con game. Since you haven’t said anything about finches that must be the source of glaudys’ assertion. It’s ironic that you and I are constantly accused of distorting gluadys’ words.

Yeah, we hear that a lot around hear. It never seems to occur to the accuser that maybe their words weren't all that straight forward to begin with.

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It's touching to see the proponents of two mutually exclusive theories bonding ;).

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ORIGINAL: Jhud

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My point is, [biological species definition] doesn't even seem to be particularly useful in your best case scenario.

It's very useful. As I said I don't have ready access to primary literature, but I checked out a few things from The Beak of the Finch. The idea that the finches do not form distinct species is not new. As long ago as 1935 a scientist by the name of Lowe described them as "hybrid swarms". But three years later, a researcher named David Lack, attempting to study the hybridization of the finches found the 13 groups very rarely interbred, even though they seemed to be following the same life-style, eating the same diet of seeds and there was no obvious adaptive difference among the groups.

What he did find is that no two groups which were very alike inhabited the same island. It was as if they had divvied up the islands to avoid competing with each other. Furthermore, when two similar species did occupy the same island their average measurements were (in the smaller group) smaller than the average of the same species on an island where it was the sole finch, and the reverse for the larger species. Again, an apparent strategy to avoid competition by enhancing the differences between them.

Although he hadn't found what the selective difference was, it seemed clear that the species preferred not to hybridize and used a variety of measures to remain distinct.

The selective advantage was discovered by the Grants when, unlike their predecessors, they came to the islands during the dry season and thoroughly studied the feeding habits of the finches then. In the wet season, when food is plentiful, all the birds tend to eat a variety of the same seeds. But in the dry season, as food becomes scarce, each population tends to specialize in certain seeds, and which seeds they survive on is closely matched by beak type and size.

So we have a situation in which the response to dry season scarcity was to lower competition by specializing in different seed types, with an accompanying specialization in beak types.

In the Grant's opinion, the rarity of hybridization (which they also observed) and the specialization in both form and function, justifies identifying the groups as separate species.

At least until 1982, the year of an El Nino event that brought flooding to the island. They had documented hybridization before, but rarely, and as expected the offspring were less fit than offspring of either parent's species. But with the changed environment after the rains, they documented a significant increase in hybrid matings, and more surprisingly found that the hybrid offspring were doing well, better in fact than either parent species.

The massive rains of 1982 also brought significant changes in available food supply—there was lots more of it, but it was also very different food. The Grants hypothesize that the increased variability introduced through hybridization is allowing the birds to adapt more easily to these new conditions.

But (in the chapter entitled “Fission or fusion”) they speculate about how long this trend will continue. They have done some hard number crunching on how many generations it would take to fuse the two populations under different scenarios. The maximum they suggest is 50 generations or about 200 years, but with strong selection and a high rate of breeding it could be much less.

The unknown question is whether Mother Nature will maintain the environmental conditions that currently favor the hybrids. If dry seasons and drought return to the islands, one may find a turn again to specialization—not necessarily quite in the same way, but there would still likely be greater advantage is drifting apart than in homogeneity.

Without a concept of species we couldn’t even talk in terms of hybridization. We need to know who mates with who at what rates and with what success to see how populations change.

I will grant that if one is clinging to a 19th century understanding of “species” as fixed and definitively separate, it is not a useful concept. But if one understands that “species” are fluid and dynamic groups that change their relationships to each other, it is a way of talking about the status of these relationships.

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Perhaps; my understanding from a broader reading of the literature is that the characteristics that distinguish the various populations (like beak size and thickness) represent a spectrum which shifts back and forth within general parameters depending on the circumstances, and don't really demark substantive barriers between populations.

Well, this time I can say that it is not as simplistic as you depict. That shifting is not incompatible with maintaining basically separate populations. A high degree of assortative mating is a substantive barrier between populations. And that is what was observed even when researchers couldn’t figure out why.

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A dinosaurian life-style for one, especially therapod dinosaurs.

Well, that is not really what I asked

A bit flippant, I admit, but essentially, it is what you asked for.

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What neccesitates a a four chambered heart?

I don’t know that anything necessitates a four-chambered heart other than having parents who had one.

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What allows dinosaurs to lead such a lifestyle? A four chambered heart.

Well, we don’t know that either. I don’t know if any dinosaur hearts have been discovered that are four-chambered. “Dinosaur” covers a lot of time, a lot of territory and a lot of diversity. When it was suggested that dinosaurs might have had feathers, I don’t think anyone understood that to mean all dinosaurs, and AFAIK, all feathered dinosaurs found come from the most-bird-like group of dinosaurs, as one might expect. Did a four-chambered heart come before or after the separation of birds from non-avian therapods?

What we know is that various dinosaur groups had different ways of living and that the group from which birds arose appears to have been a particularly active group with high energy needs. Were they active because they already had a four-chambered heart or did the level of activity favour the selection of a four-chambered heart? Without information on just when the four-chambered heart developed, this is a chicken-and-egg question we can’t answer.