Daniel Smith: And you couldn't figure that out by reading?

No, I couldn't figure it out by reading. I specifically discussed what I read and why it puzzled me. Did you miss that?

Do you do this everywhere… crash funerals and ask why they are honoring the dead person?

The analogy here is hearing about someone important dying, going the the funeral to pay my respects, then quietly and respectfully asking my friends at the service why the memorial involved nothing but poking other people in the eye and saying, "Ah, that's why I miss him." It would strike me as faint praise until someone explained to me that the problem was that the people getting poked in the eye just didn't get the joke.

I posted to this thread to ask why John A. Davison was being honored.

And you couldn't figure that out by reading?

Do you do this everywhere… crash funerals and ask why they are honoring the dead person?

Go away Don. There's a time and place for what you do and this ain't it.

I was saying that chromosome rearrangements are not likely to have been a major driver of speciation, in the past or the present. Davison also seemed to think chromosome rearrangements belied Darwinian gradualism, which is ridiculous. They are mutations in the very basic sense, which Dobzhansky clearly stated in Genetics and the Origin of Species; as such,they are subject to the rules of basic population genetics, just like point mutations.

Which brings me to a critique of Davison’s “Manifesto”: he seems familiar with some of the cytogenetic literature, but has an almost complete lack of understanding of population genetics. This cripples his analysis, as we shall see below. First, a long (sorry) quote from his manifesto (my emphasis is in bold, Davison’s emphasis is in italics):

Any hypothesis of organic evolution must stand in accord with
the realities of cytogenetics. What is critically relevant to
the argument presented here is a simple question: Were chromosome
restructurings effected sexually, as the Darwinian view demands, or
were they produced by some other means? The Australian cytologist
Michael J.D. White had a number of very pertinent remarks to make
on this issue. Here are several which go directly to the very heart
of the matter:

The conclusion we must draw from these facts (and a great many
more instances of the same kind in beetles, mammals and in
fact in almost every group of animals whose chromosomes have
been studied) is that, in certain groups at any rate, fusions and dissociations which exist as cytotaxonomic differences between species have not been preceded by a condition of balanced polymorphism in an ancestral population.

(my emphasis)
Animal Cytology and Evolution
(1973), page 765

It seems safe to predict that any discussion of the broad
mechanisms of evolution in, say, twenty-five years' time,
will have to take far more account of the chromosomes
themselves as bodies composed of nucleic acid and proteins,
and their relations to the rest of the cell at various stages
of mitosis and meiosis. And, as indicated earlier, it will
almost certainly lay more stress on the role of chromosomal
rearrangements in initiating and promoting speciation.

(my emphasis)
Ibid., page 783

Referring to the many chromosomal rearrangements that have occurred
in the evolution of the species in the genus Drosophila, White
offered the following comment.

The evidence in favor of the view that many cytotaxonomic
differences have arisen without passing through an adaptive
polymorphism stage has been growing steadily. Even in
Drosophila the fifty-eight fusions have most likely
established themselves without benefit of heterosis.

(my emphasis)
Ibid., page 768

White's language is unmistakable. He has surmised that the
chromosome restructurings were, in all likelihood, not produced
sexually. Once again we witness the complete failure of the
Darwinian model. I submit that if they were not produced sexually,
there remains only one other conceivable way they could have been
produced and that is semi-meiotically as I have indicated. If there
is another way, I can only hope that someone will enlighten me!

Davison’s interpretation of White (whose book I have read, by the way) is almost laughably wrong. White is not even close to saying that the rearrangements were not produced sexually. When he says “Even in
Drosophila the fifty-eight fusions have most likely established themselves without benefit of heterosis”, he simply means heterozygotes for the rearrangements were not fitter than the homozygotes. That’s what “heterosis” means. When White talks about “balanced polymorphisms”, he is, of course, referring to the same thing. A balanced polymorphism is a polymorphism that is maintained in a population because the heterozygote is the fittest genotype (think of the sickle-cell situation genotype in humans). We know how rearrangements can be established in populations, even when selection is against the heterozygote. Papers by Sewell Wright, Russel Lande, and Phil Hedrick illustrate this, and in none of these scenarios is it a requirement that the rearrangement not be produced sexually. So, how Davison ever came to this conclusion regarding White’s remarks is a mystery, because he never elaborates. He just says that the Darwinian model is dead. LOL.

Since John almost always signed off with "A past evolution is undeniable, a present evolution is undemonstrable", I doubt if he'd be surprised that chromosomal speciation does not occur today. I believe he was of the mind that chromosomal evolution had pretty much played out several million years ago.

The object of war is not to die for your country but to make the other bastard die for his.

and

May God have mercy upon my enemies, because I won't.

and

It is foolish and wrong to mourn the men who died. Rather we should thank God that such men lived.

The Increasingly Isolated Dr. Miller – Telic Thoughts…

A further problem with chromosomal speciation is that it depends critically on the semisterility of hybrids who are heterozygous for chromosome rearrangements. It is not widely appreciated, however, that heterozygous rearrangements theoretically expected to be deleterious (e.g., fusions and pericentric inversions) in reality often enjoy normal fitness, probably because segregation is regular or recombination is prevented… Any putative case of chromosomal speciation requires proof that different rearrangements actually cause semisterility in heterozygotes, and almost no studies have met this standard.

Coyne JA & HA Orr (1998). The evolutionary genetics of speciation. Phil.Trans. R. Soc. Lond. B 353: 287-305.

Another mechanism that Coyne and Orr fail to mention is meiotic drive, which can be a powerful force in blunting negative selection against a rearrangement. In humans, it may be the biggest contributor to the fixation of the fusion that resulted in human chromosome 2.

Regardless, I still enjoyed Davison's wit, and miss him.

Daniel Smith: Why are you posting in this thread?

I posted to this thread to ask why John A. Davison was being honored.

Why are you posting in this thread?