Agnos1

Try as I might I really don't see anything incorrect in Dawkin's thinking. All changes do start at the genetic branching level and errors in code produce change from time to time. Whether that individual who's carrying the genes lives or not has much to do with biology and the environment. The fact that favorable/unfavorable changes affect the population is only secondary. Dawkins goes further in saying that the individual organism is only "secondary" to the DNA strand. A lot of people, not only religionists, don't like this idea that we're only vehicles for DNA expression. However, approaching it from Gould's PE viewpoint works well for those more into the forest instead of the trees. Here is a link to a summary by Gould who actually e-mailed me with some of this thoughts before he died so I feel fortunate. Mostly I believe that any dispute between Gould and Dawkins was illusory and that they both were taking different routes to saying the same thing about evolutionl.

<a href="http://www.brembs.net/gould.html" target="_blank">http://www.brembs.net/gould.html</a>

[ October 15, 2002: Message edited by: Agnos1 ]

[ October 15, 2002: Message edited by: Agnos1 ]</p>

Doubting Didymus

There is only one level of selection. Ask yourself: what does a parent pass on to its offspring? Genes. Nothing but genes can be selected for, which is obvious if you think about it, but that is all Dawkins is really saying. He accepts 'higher levels' of evolution, such as improved embryologies, but even so it is the genes for embryology that are passed on and selected for. Since nothing else can be passed on to the next generation, nothing else can be selected.

Dawkins has never characterised PE as hopeful monster. He explicitly rejects this interpretation, which he says is a creationist misrepresentation. Perhaps you misread the chapter?

The Lone Ranger

Goulds' and Dawkins' thinking was far more alike than either of them seemed to want to admit. I think the whole "Punctuated Equilibrium vs. Phyletic Gradualism" flapdoodle was a tempest in a teacup. The thing is, you're dealing with two brilliant and somewhat egotistical people (I can't speak about Dawkins, but I've met Gould, and while he was certainly brilliant, he wasn't shy about letting you know that he knew it, too).

Dawkins and Gould seemed to be incapable of writing about each others' ideas without exaggerating almost to the point of charicature. That said, I tend to see "macroevolution" as nothing special, just "microevolution" on a larger scale.

Population geneticists like Russell Lande have shown pretty convincingly that you would expect speciation events to occur relatively rapidly, and then for stabilizing selection to kick in and keep populations relatively stable for considerable amounts of time, assuming a relatively stable environment.

I guess the whole thing gets blown out of proportion, but Gould often acted as if he thought most paleontologists were idiots. (Have you read his '72 paper in Paleobiology? It's downright condescending in places.) My impression is that few paleontologists or evolutionary theorists were ever convinced that evolution occurs at a gradual and unchanging pace.

Heck, Darwin himself mentions in the Origin that once a species has become well-adapted to its environment, there's no reason to expect it to change much further. And Mayr had laid out much of the groundwork for what later became incorporated into the notion of PE decades before Gould and Eldridge.

Dawkins, by contrast, sometimes seems to think that Gould's idea of PE was something closer to saltation. While I tend more toward Dawkins in this case (Gould did make some pretty grandiose -- and in my opinion, unsupported -- claims), I don't think that either of them was being entirely fair in evaluating the other's claims.

That said, I think Dawkins was spot-on in saying that there's nothing special going on during periods of "punctuation," and that Gould's claim that PE represents a "new and general theory of evolution" is a gross exaggeration.

***

Not in Our Genes? Ah, I didn't think very highly of it. Ideology disguised as science was my impression.

Cheers,

Michael

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Doubting Didymus

From what I understand about the terminology, 'macroevolution' does not refer to large scale biological change. Macroevolution does not mean change between kinds, or anything of the kind. It refers to certain global patterns that occur over a long period of evolutionary history. Thus, it is bringing ecology and non-biological factors into the evolutionary picture.

To me, it makes no sense to call macroevolution 'evolution' at all. I will repost something I posted on this topic a while back:.

pz

You can't select for genes. You can only select for a phenotype. It's also trivially false that only genes get passed on to the next generation. The issue is significantly more complex than you are making it out to be.

You definitely need to read some Lewontin or Oyama.
I was referring specifically to the characterization in the first post in this topic. However, both Dawkins and Gould have wobbled about quite a bit on their characterizations of their own and each other's theories.

pz

I have to disagree. Lewontin is one of the few authors out there who can lucidly argue against gene-centric dogma, and give the proper weight to a more pluralistic view of biology.

If you want ideology, try Pinker. There's a guy I find infuriatingly simplistic and just plain wrong.

Doubting Didymus

Fill me in. Obviously the total phenotype is selected as a whole, but phenotypes are not passed on. Educate me. What else, other that genes, are passed on?

Why can't you select for genes? The natural selection of a desirable trait is, indirectly at least, selecting the genes that produce that trait.

pz

Phenotypes aren't passed on? You mean you don't look anything like your parents?

If the phenotype isn't passed on, then how can you select for it?

Much more than genes are passed on to the next generation. Eggs are complete, functional cells, packed with highly non-trivial things like ribosomes and centrosomes and membranes and so forth. The usual analogy is that the DNA is like a record, and yes, it's important and is passed on...but the progeny also get a completely assembled record player.

I would also add that there is a third player, the environment. Phenotype is a consequence of a three-way conversation between genes, cytoplasm, and environment, and it's always a mistake to focus on one and neglect the others.
"Indirectly" is the operational word there. Selection can only work on the phenotype (with a few possible exceptions, depending on how you define things), and the genes get dragged along for the ride.

Doubting Didymus

What? surely you know the difference between a genotype and a phenotype? Passing on phenotypes is lamarkism. I do not have my father and mothers phenotype, I have a combination of their genotypes.

Well, quite. You can't, really. You can only select for the genes that built it.


But what effect do these features have on the end product? Some, obviously, but not a lot. In theory, if you fertilised an egg cell, then immediately removed the nucleus and inserted it into the egg cell of a different woman, the child would become the same (or at least extremely similar) as a child formed from the same genes, but using the original mothers egg.

Also, while it is true that some organelles replicate exact copies of themselves, many do not. The difference is that mitochochondria, for example, have genes. Thus, a mitochondria inherits features from its parent mitochondria. A membrane, however, can not pass any of its features on to the next membrane, and thus it can not be selected to pass any features to the progenies membrane.

I agree that there is a three way conversation in the production of a phenotype, but the creation of a phenotype is not evolution. Of the three things you mention, only genes can pass features to the next generation. Imagine a lion, say, with a relatively poor set of genes, but with excellent cytoplasm and a superb environment to grow in. The beast might become very successful because of these factors, but how is it going to pass its success on? It can't. Of the three factors, only the lions genes can be given to the next generation.


Natural selection chooses the best phenotype. That phenotype then passes on its genes. Does the offspring inherit the phenotype? Absolutely not, only the genotype.

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Oolon Colluphid

Oh come on pz! I can’t believe I’m replying to you like this... please take this with a slightly incredulous .

No, phenotypes are not passed on. Much of what goes into making a phenotype is to do with the environment during development -- nutrition, for instance. But someone with rickets can have non-rickets-y offspring if the offspring get enough vitamin D. Is rickets not however part of the phenotype? Come to that, aren't healed injuries?

What is passed on is the genes that, together with environment, produce a given phenotype. (Dawkins has repeatedly stressed that this intertangling is why it is stupid to speak of a literal 'gene for' many traits. Phenotypes are always genes + environment.)

Phenotypes are what selection acts on, sure. But only one part -- the genetic component of the phenotype -- makes it to the next generation to make another phenotype. So evolutionarily, the only relevant bit is the genotype. Which is why evolution isn’t a change in phenotype frequency in a population over time, it is a change in allele frequency.

Whoa there! And eggs come from where, exactly? Surely not from cell division? What makes a cell the sort of cell it is? Might it just be the genes it contains? And what makes cells in a particular tissue undergo meiosis? Isn’t it the genetic instructions they contain?

Sure. But will those very bits make it into the next generation? No. They get copied. And what actually gets copied? The genes... isn’t it? You make a reasonable case for gametes as the units of inheritance... but hardly the phenotype! What affects what the egg grows into? Surely not genetic instructions being turned on and off during development (plus environment, as above)? Evolution is about change in something across time. So that which has the most longevity, which is around for the most time, is what counts. And that is the patterns in the DNA. If a centrosome changes in some way over time, it will do so because of changes in the genes that built it (coded for the proteins which folded in such a way....).

Then the analogy is false. In order to get to the next generation again, a whole body has to get built -- one that can survive long enough to reproduce in its environment -- and it gets built according to the recipe coded in the genes in each cell. The record player is very far from already assembled. A mammalian egg also requires a uterus. Does that get passed on too? It is at the least the motor, and maybe the pre-amp, for this record player.

Actually, now I think about it further, I’ve heard that analogy before, and it is right, except you’ve misunderstood it. The record comes with instructions on how to build a record player. (Thinking even further, the analogy may even be Dawkins’s!)

Sure. And how exactly is the environment passed on (except in the obvious, trivial sense)? What does the evolving -- the environment?

Sure. But generally I don’t. Nor does Dawkins. Maybe you should re-read some of his stuff sometime? Extended Phenotype, rather than the more popular books, would be the place to start ( / return) to him.

And it’s not a mistake to focus on genes, when what we’re discussing is what it is that’s passed on. Injuries aren’t; obesity isn’t; rickets isn’t. Phenylketonuria is, Down syndrome is, a tendency to be obese may be.

Other than that, I’m rather bemused. Hey, I’m no expert, but I do tend to agree with Dawkins. Perhaps you could set me (and him) straight?

Cheers, Oolon