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

[prester-scott.livejournal.com]

I'm afraid I really don't find "punctuated equilibrium" any less unbelievable than "macromutationism."

What mechanism causes mobility between major forms in such a short time (whatever "short" means)? Environmental adaptation only? X-rays? Fairy godmothers?

And maybe I just don't understand what I'm reading, but I fail to see how you can make the sweeping generalization "puntuctuated equilibrium fits the facts of the fossil record pretty well" based on that article. The studies quoted appear to be saying that species are stable, not that species mutate into other species over geologically short periods; the latter conclusion still appears to be an assumption based on negative evidence. If gradualism requires that there be 1 million years' worth of transitional forms, but PE only requires 10,000 years' worth, then if you find no transitional forms, PE becomes easier to defend, but that's still a long way from proof.

[rowyn]

It "fits the facts" in the sense that it does not directly contradict them. The facts do not directly contradict "God said 'let there be light'", either. But they do directly contradict things like "The earth is flat and rests on the backs of four elephants standing on a turtle shell."

The fossil record, as I understand it (and I may be wrong) is not precise enough to pinpoint transitional forms in a "short" (geologically speaking) period of times. Punctuated equilibrium says that changes from one species happened too quickly for us to see them by looking at the fossil record, in most cases. Further, it contends that most species don't change very often. The fossil record will show, say, a new worm species suddenly popping up ten to eleven million years ago, different but not wholly dissimiliar to pre-existing worm species. Then it stays almost exactly the same for 10 million years. Gradualism has trouble with this concept, because gradualism wants everything to always be in flux to the next species.

Gradualist proponents say "You can't see transitional forms because the fossil record is grossly imperfect [which it is] and just happens to not have preserved them", which is possible but not very satisfying. Puncuated equilibrium says "It happened too quickly for the rocks to notice" which isn't proof, but which is more plausible. You could also say that the Creator made new species out of clay and planted them fully formed on the earth at various points in history, and it would also fit the same fact. But punk eke also meshes with the theory of natural selection, and with what evdence does exist of transitional forms.

I will poke around later to see if I can find a clearer explanation of the whole thing. Gould is usually easier to follow than this particular article was, and I should think that, having made a career of evolutionary study, he will have a better shot at convincing you than I possibly could. ;)

[prester-scott.livejournal.com]

Punctuated equilibrium says that changes from one species happened too quickly for us to see them by looking at the fossil record, in most cases.

Yes, I know; that's what troubles me about it. It is unverifiable. What good is a scientific theory that is unverifiable?

I might be more inclined to believe it if some believable rationale were offered: how, exactly, does one species transform into another (at whatever "speed")? It isn't obvious to me that "natural selection" can explain everything. That sounds just as hand-wavey as "God did it." Judging by the way natural selection actually works, it seems that it sticks us back with gradualism, which we've already agreed is implausible. (Unless I just don't understand how natural selection works, which I admit is possible.)

Gould is usually easier to follow than this particular article was...

Yeah, that one was pretty thick for saying so little. I fear that he may be too biased not to argue for his own theory. He warned as much in the article.

[level-head.livejournal.com]

Hello, Prester_Scott and Rowyn,

If I may interject a bit into this conversation with your permission...

Speciation, surprisingly, often happens instantly. DNA is wound up onto protein spools called chromosomes, to keep it organized. Every time the cell divides, there is a chance that this mechanism gets messed up. If the cell happens to be a reproductive cell (spermatozoa or oocyte) then the resulting sperm or egg cell will have a different chromosome count.

Most of the time, this is fatal, but not always. In fact, there are some often unfortunate conditions that occur when the extra or damaged chromosome is either the X or Y. However, sometimes the only thing that really happens is that the new organism can reproduce with the parent stock only with difficulty.

Once there are enough offspring to establish a small population, the "new counts" can interbreed readily, and often can no longer interbreed with the parent stock. This can take place in two generations. It helps if they're Southern. ];) (My family is from West Virginia.)

Perhaps six million years ago, this happened to us. In humans, chromosome 2 is clearly recognizable as chromosomes 2p and 2q in the chimp; all the others match up very nicely. So, humans have 23 pairs, chimps 24 pairs. They can interbreed, if at all, only with difficulty. (I won't use the Southern comment again.) ];)

So, the speciation, which is really genetic isolation, can come about very quickly.

Once a population is genetically isolated, the two groups drift away from each other. Recent work with moths show that obviously different species, by appearance, can come about in approximately six generations. It's a subjective measurement, but we all know of mutations that have made for very different-looking humans, and very different acting ones. Once in a while, this is a survival advantage, and takes root in the population.

Punctuated equilibrium is simply the recognition that thus speciation can happen quickly.

Since only perhaps one millionth of one percent of the vertebrates ever get a chance to fossilize, the "intermediate species" argument is rather a chuckle to me.

Remember when whales were the big thing with creationists? "Show me a whale that lived on land! Show me a whale only partially adapted! What was [i]this[/i] part used for, or [i]that[/i] part?"

Now, due to some fortunate finds in the Middle East, we've got intermediate whales running out the kazoo. But now creationists want the intermediates between the intermediates. As we find those, they'll want to slice [i]that[/i] pie too.

There is no such thing as an intermediate species. Or, put another way, they all are. We all are.

The avian/reptile business is another area of amusement. "This has features of its therapod (small biped dinosaur) ancestor, and beginnings of its bird legacy." The answer comes back "No it doesn't. It's OBVIOUSLY a true bird. Uh, with teeth. Um, and claws on the wings. Well, it's OBVIOUSLY just a dinosaur. With, ah, feathers and beak, and, am, extended forelimb bones to support a wing structure."

The more you learn about this, the more obvious it gets. And no evidence has been presented otherwise; I have investigated a great many creationist claims and found them not only wrong, but dishonestly so. They will sometimes admit the mistake, and show up on another list touting this mistake as "the unchallenged truth". THAT, more than anything else, is the aspect that annoys me, and I have personally caught a number of creationists doing exactly this.

===|===============/ Level Head

[prester-scott.livejournal.com]

Okay, you've supplied a believable mechanism by which changes might occur.

But this leads me to ask: how likely is it, really, that DNA coding errors will lead to a beneficent mutation which occurs simultaneously in enough members of a population that they're able to breed into a new species? You invoke studies of moths: is this actually something that's been tested, and is empirically verified, or is it something that "can" happen according to someone's theoretical calculation? Big difference there.

And what about that pesky fossil record? You seem to imply that it really isn't much good for proving anything. Lack of evidence does not prove any theory (although it may disprove some theories).

I hold no brief for creation science, so called. But neither will I accept statements on faith from people who often have theological (or perhaps, anti-theological) subtexts lurking behind their scientific research.

[level-head.livejournal.com]

Sorry about the delay; life intruded there for a bit.

"Okay, you've supplied a believable mechanism by which changes might occur."
It is important to note that this is not just "might occur"——we see this happen in populations, our own and others.

Also, any hypothesis worth consideration makes testable predictions. This one, that chromosome count changes lead to species separation, predicts that organisms that reproduce asexually would have greater speciation, as they don't have to worry about matching them up again. Also, that the greatest genetic diversity would be self-fertilizing plants, as they would have both the male and female contribution from the same parent, and thus the same chromosome count. Both of these predictions match what we observe in nature.

In fact, humans have about three-billion base pairs in their DNA. There are species of amoeba with more than 600 billion. And within the human cultivation of plants on this planet, wheat has separated from etter grass; there was a chromosome duplication, and the two can no longer interbreed at all. But wheat and etter grass have greatly diverged since then; this has been in a relative eyeblink in history. We don't get much fossils of grassy plants, or in fact much fossils at all; but fortunately we could see this happening historically.

"And what about that pesky fossil record? You seem to imply that it really isn't much good for proving anything."

Well, the fossil record is sporadic at best, although there are literally billions of microfossils; these tend to preserve better, but are unsatisfying to laypersons. But, nevertheless, what we see is entirely consistent, with good predictability. For example, we had very early tetrapods, still aquatic, from 370 million years ago, then a gap, then a better, more land-capable tetrapod from about 330 million years ago, with many changes. We had nothing from that gap in the Devonian period of this creature type.

Just months ago, we found a critter from halfway between——350 mya——and it looks just like what one would predict from the ones before and after. Transitional.

"Lack of evidence does not prove any theory."
True. And neither does evidence. Science doesn't work that way; one can never prove a theory. It simply works. It is possible to prove it wrong, or incomplete——and at this task creationist have labored for a hundred plus years without success. The theory of evolution (TofE)is refined at the edges, and scientists are motivated to make this refinements seem "revolutionary". But the core has remained stable, and all of modern biology and medical research is built on this core. By Christians, Hindu, atheists, and all sorts of different philosophies.

The results speak to all of these people. In spite of the vehement disagreements that people (especially scientists!) seem prone to, the scientists working in these fields are way over 99% agreement on the TofE.

You ask what the chances are. They are very small indeed. But only those (and neutral changes) get preserved, and nature has large amounts of population and time to play with.

The moth study was reported in an issue of Science a few weeks ago.

And mutations (the same mutation, anyway) don't generally occur simultaneously with a population; that's not necessary at all. Once you realize that, the "odds" change dramatically.

Do you accept that mankind and chimpanzee share the same ancestor?

===|==============/ Level Head

[prester-scott.livejournal.com]

I have to admit the evidence you present is persuasive, even though I really still don't understand the science behind it.

In particular, I have this question:

And mutations (the same mutation, anyway) don't generally occur simultaneously with a population; that's not necessary at all. Once you realize that, the "odds" change dramatically.

Why isn't this necessary? I can see why the "chances" would be reduced in asexual or hermaphroditic organisms, but sexual reproduction requires at least two...

[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.

Re:

[level-head.livejournal.com]

Sexual reproduction mixes two genomes, certainly. But to take eye color as a well-known example; you might have a parent with brown eyes, and the other parent with blue eyes. Yours will be one or the other, but as brown eyes are "dominant", you would have needed to inherit a recessive (and hidden) blue eye gene from the brown eyed parent.

In other words, for one parent to have blue eyes, both genes she carries (I'll just pick a gender here) must be for blue eyes. If either one was brown, she'd have brown eyes instead.

The other parent [i]has[/i] brown eyes, but this means either that both genes code for brown eyes, or that one of them is a hidden blue.

Offspring get one gene from each parent.

Offsping in the first case can only be "brown-blue", which means that they will ALL carry the recessive blue-eyed gene (and can pass it on) but all will have brown eyes.

However, if the brown-eyed parent is "mixed", theoretically half of the offspring with a blue eyed other parent will have blue eyes.

Side note: Genetic odds don't really work with small numbers; there could be ten brown eyed children or ten blue eyed or any combination. Now if they had [i]lots[/i] of kids, it'd work out. But their finances wouldn't. ];)

I've over-simplified the eye color business, but this is how it works in principle. Throw green eyes and hazel eyes in the mix and it gets more difficult to see clearly.

In any event, picture a useful trait such as a longer than usual neck, or a slower metabolism, or a whatever might be useful in the circumstances happening to occur. (Or, a neutral trait such as brown eyes.) If this is associated with a dominant gene, it will take only one parent to pass it on.

Make sense?

===|==============/ Level Head

[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.

===|==============/ Level Head

[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. ];)

===|==============/ Level Head

[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.

===|==============/ Level Head

[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..