"Macro" vs "Micro" genetic "kind" mechanism?

Potentially, but I think the issue is more a matter of 'natural variation' versus 'mutation.' One issue with the homeostasis experiments described above is the fact that they used artificial selection (instead of natural selection). Artificial selection essentially 'evolves' one or a few traits using existing natural variation (for the most part), and at the expense of all other traits - often it doesn't matter since the animals are captivity, free of all natural selection forces in the wild (imagine a pack of (artifically selected) dachsunds trying to compete with a pack of (naturally selected) wolves in the wild...)I guess I'm saying that these artificial breeding experiments don't tell us much about natural selection - where it is important to retain a certain degree of genetic 'flexibility'/adaptability while specialization evolves.But yes, you are correct in that anyone using the 'genetic homeostasis' experiments as refutation of macroevolution is simply ignoring the potential for mutation. I'm guessing if you repeated the Drosphilia bristle experiment with a population of flies given a chemical mutagen, the range of the phenotype would be extended.

There is also the limit to which a trait can be pushed before the energy needed to {make \ maintain \ use} that trait interferes with the rest of the bodily functions.This is why you cannot breed horses to run at the speed of sound. There is a point where bones get too weak, heart and lungs not capable to keep pace even though the legs are "willing"There are trade-offs.

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we are limited in our ability to understand
by our ability to understand RebelAAmerican.Zen[Deist
{{{Buddha walks off laughing with joy}}}

There is one thing that may have held back human evolution of a larger brain -- the size of the female pelvic girdle. Is this going to become an historic footnote now that cesarian sections are becoming common?Just a thought.

i don't think they're common enough now, or common at all long enough to have effected much of anything.

Possibly, but it seems loss of enormous jaw muscles was a important milestone in allowing the capacity of the human skull to increase. For a very interesting paper:
http://www.ncbi.nlm.nih.gov/...
{Shortened display form of URL, to restore page width to normal - Adminnemooseus}Bigger also doesn't necessarily mean better; I'd like to think that further evolution of the brain will involve better utilization, rather than big bulbous heads...It is an interesting point though, a sort of chicken-or-the-egg kind of question. Which came first? Increased pelvic girdle or increased fetus size? (Hopefully the pelvic girdle for both parties involved, but I'm guessing it happened both ways through evolutionary history...)This message has been edited by Adminnemooseus, 07-07-2004 10:42 AM

Nice article. I thought it was a retained infantile structure (as in chimps babies look more like human babies than than do the respective adults). Well I guess that is the same if the adult muscle structures are repressed.thanks

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we are limited in our ability to understand
by our ability to understand RebelAAmerican.Zen[Deist
{{{Buddha walks off laughing with joy}}}

That is really interesting. However, I did not realize that the creo crowd was basing their genetic "limit" on this...Johnson seems to argue that since with artificial selection, one does not change a dog into a horse dramatically they must be genetically limited though he provides no support for this (and ignores the fact that dog breeders are selecting for specific characteristics). Could you give me a reference for the genetic homeostasis work? I would like to read up on it.Cheers,
M

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Could you give me a reference for the genetic homeostasis work? I would like to read up on it.

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Lerner's book, Genetic Homeostasis, is available online: Genetic homeostasis: Core Historical Literature of AgricultureKC

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However, I did not realize that the creo crowd was basing their genetic "limit" on this...Johnson seems to argue that since with artificial selection, one does not change a dog into a horse dramatically they must be genetically limited though he provides no support for this (and ignores the fact that dog breeders are selecting for specific characteristics).

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They get much of this from Richard Milton's "Shattering the Myths of Darwinism":

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This is Darwin's central idea of evolution in a nutshell: bears can become whales, or whale-like, given enough time and enough natural selection. However Darwin withdrew this claim from the second and later editions of the book.

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Almost certainly this was because as an animal breeder he knew from first hand experience that no plant or animal breeder has ever succeeded in producing a new species by selective breeding. Primarily this is because of what Harvard's Ernst Mayr called "genetic homeostasis" -- the barrier beyond which selective breeding will not pass because of the onset of sterility or exhaustion of genetic variability.

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Of course, besides getting Lerner's name wrong (Milton gets HIS info from a botched quote in a terrible book that I can't remember right now), the concept of genetic homeostasis is misunderstood.From: No webpage found at provided URL: http://www.alternativescience.com/shattering-the-myths-of-darwinism-contents.htmEDIT: the bad book was Jeremy Rifkin's Algeny. If you get a copy of Stephen Jay Gould's An Urchin in a Rain Storm (I think that's the title), you will find Gould's review of the book very entertaining.KCThis message has been edited by KCdgw, 07-07-2004 10:33 AMThis message has been edited by KCdgw, 07-07-2004 10:42 AM

Thanks a bunch KC, for both the science reference and the reference to Milton's work. I'll check them out.I saw Rifkin give a lecture when I worked at the American Museum of Natural History. He was debating an agriculture department spokesman about GMOs...Rifkin talks like a preacher and argues like a creationist..so his book being botched is not surprising.

hey RAZD, another interesting article regarding brain size evolution just appeared in PNAS - apparently binocular vision refinement is associated with increased brain size in primates:
From The Cover: Binocularity and brain evolution in primates - PubMed

Thanks. I have seen something before on {brain size of squirrels being larger than that of rats for the same body mass} being attributed to the squirrels 3D environment processing ... it would be interesting to compare there degree of binocular vision, both being fairly low on the overlap scale (due to need to be aware of predators)

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we are limited in our ability to understand
by our ability to understand RebelAAmerican.Zen[Deist
{{{Buddha walks off laughing with joy}}}

pink sasquatch writes:

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Also, even if the Y chromosome did disappear in a few hundred thousand years, there would still be men, they'd just be XO instead of XY.

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Um, no.XO individuals develop as female. It's called "Turner's Syndrome." It is considered to be the most common chromosomal abnormality in humans (though only about 1% of those who have it survive to term).

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Rrhain
WWJD? JWRTFM!

RAZD responds to me:

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isn't Przewalski's horse smaller and genetically older?

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That I don't know. I'd have to look it up.

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Rrhain
WWJD? JWRTFM!

RAZD writes:

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I believe there are some species where the sex determining gene is missing.

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Well, the effect of not having a sex-determining gene is different across species. In humans, for example, XO individuals are sterile and have other developmental abnormalities (not to mention that most XO fetuses fail to make it to term). In mice, however, XO individuals tend to be fertile. In horses, XO individuals are viable and have few physical differences, but tend to be irregular in their estrus cycles.YO individuals, however, are unviable in humans.In some species such as some insects, sex is not determined by the presence or absence of a sex chromosome per se. Instead, it is the ratio of sex chromosomes to autosomes. There is only one sex chromosome and if you have a greater ploidy of sex chromosomes to autosomes, you're one sex. Otherwise, you're the other.And then there's birds where the sex chromosomes go the other way: XX individuals are male and XY individuals are female.

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Rrhain
WWJD? JWRTFM!