Evolution, Part Two

[rowyn]

I found an article on the theory of punctuated equilibrium, which it turns out I massively mangled in my previous post on evolution. Or, rather, didn't address at all. What I described as "leap from one species to brand-new species in a single generation" is known as "macromutationism," and has little, if any, following. "Punctuated equilibrium" theorizes that new species evolve from previous species 'quickly' only in the geological sense. "Quick" in this case means mere millenia, five to ten thousand years. Darwin's original theory offered "gradualism", or change in species over millions of years.

Puntuctuated equilibrium fits the facts of the fossil record pretty well, and isn't as unbelieveable as macromutationism. Haven't read enough on it to say whether it's provable or disprovable based on evidence, but it seems to be the basis for useful research, so I'm happier with it. :)

Comments

[rowyn]

While you've made several good points, I think you've neglected to address a sticking point: how does a sexual species mutate into a new species?

An example: let's say, by random chance, a bird hatches out of a lizard egg one day. If the bird represents a new species, then it will not be capable of reproducing, unless, by sheer coincidence, a compatible bird happens to hatch in the same generation. This is what makes macromutationism so implausible.

As I understand it, the punctuated equilibrium model is more complex to explain. An example of it might start with a population of a single species. Minor variations, which do not prevent interbreeding, occur in the population all the time, but mostly they are of no benefit and/or chance swallows them up again. However, if something happens to separate the smaller population away from the larger, then mutations in it stand a better chance of taking hold -- the "Southern" syndrome you refer to earlier. As long as the smaller population remains separate from the larger, chance may take it farther from its roots, until eventually enough variations have taken place that it can no longer interbreed with the original population. Thus, it becomes a new species.

[level-head.livejournal.com]

Arrgh. A long post lost. Probably happier for readers, anyway. ];-)

Briefly: Birds didn't hatch from lizard eggs; the transitionn took place over millions of years, and there's no way to draw a bright line and say this is bird, that is reptile. In a number of respects, birds are still very reptilian. Now we know why.

Your last paragraph sums it up nicely.

I would be very surprised to see "macromutationism" supported by an evolutionary scientist. I cannot imagine it, if that's what it purports to be. It is certainly not what punk eek suggests.

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[rowyn]

Well, my bird/reptile example was probably excessive in its ludicrousness. My point is that you wouldn't want to look to the fossil record, point at it and say that Snail Species A existed 10 million years ago, and the first example of Snail Species B is 9 million years and from this conclude that the first members of Snail Species B were hatched directly from members of A, and that there were no points when the species were not yet fully differentiated.

Re:

[level-head.livejournal.com]

You might conclude that, depending upon the characteristics of the two snails. It is limited, as different species, genetically isolated, look to us like the same species at first in the fossil record. We only call them different species when the bones are different, when in fact speciation happens long before significant (or any) bone differences.

For example, if there is an unusual aspect of calcium deposition on the inside surfaces, or a curious shape in the chamberization (all fossilizable) and B has this like A does but no others, it's a good bet that B came from A. The details make all the difference, of course.

The effect of this is to make species appearance more "sudden" than it really is. The B snail could have had different feeding habits, coloration, tidewater instead of deepwater for marine species, all sorts of possibilities that don't necessarily reflect in the shells themselves.

Gould was a mollusk fellow; they spoke deeply to him. I'm more of a reptile guy myself. ];)

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[rowyn]

OK, that's it, next time I bring up this subject I'm going to find some REAL examples to use instead of making them up. :) You get the idea, though.

Re:

[level-head.livejournal.com]

I'm sorry; I was genuinely trying to helpful.

I certainly was not making fun of you! In fact, I'm treating as a serious question something that you're not quite intending to be serious, perhaps? ];)

I'm going to go look at the thread and see if I can figure out where I've gone wrong.

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[rowyn]

Oh, don't worry about it. You have been quite helpful. :) My trouble is that by not having an actual example of what I'm trying to refer to at hand, I tend to distract from my main point rather than add to it. So you end up commenting on the flaws in my examples, as well as on whatever my focus is. Er. If that made sense. :)

Anyway, I'm reasonably satisfied with my understanding of the theory now. In part, my reference to "getting some real examples" is based on the feeling that only more solid data will mke me feel more comfortable with the material. Your example of wheat and etter grass, for instance, was a very useful illustration..