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Author Topic:   "Macro" vs "Micro" genetic "kind" mechanism?
Mammuthus
Member (Idle past 6475 days)
Posts: 3085
From: Munich, Germany
Joined: 08-09-2002


Message 11 of 248 (122043)
07-05-2004 5:49 AM
Reply to: Message 10 by arachnophilia
07-05-2004 4:39 AM


Creationists do even better, Phillip Johnson in his collection of mistatements, out of context quotes, and outright lies otherwise known as the book Darwin on Trial, claims that species possess a genetic limit to variation. This is stated as a "fact" in his book yet no supporting evidence or reference to such a limit is given. This fictional limit is used to explain the barrier between micro and macro evolution.

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Mammuthus
Member (Idle past 6475 days)
Posts: 3085
From: Munich, Germany
Joined: 08-09-2002


Message 67 of 248 (122576)
07-07-2004 3:57 AM
Reply to: Message 59 by KCdgw
07-06-2004 11:09 AM


Re: Limits to Macroevolution
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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Mammuthus
Member (Idle past 6475 days)
Posts: 3085
From: Munich, Germany
Joined: 08-09-2002


Message 70 of 248 (122699)
07-07-2004 11:56 AM
Reply to: Message 69 by KCdgw
07-07-2004 11:32 AM


Re: Limits to Macroevolution
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.

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Mammuthus
Member (Idle past 6475 days)
Posts: 3085
From: Munich, Germany
Joined: 08-09-2002


Message 85 of 248 (123918)
07-12-2004 10:25 AM
Reply to: Message 76 by Rrhain
07-11-2004 8:25 AM


Re: Limits to Dachsunds
Like cows like people...there was a kid in Germany born with a homozygous mutation in the myostatin gene..he is 5 now, built like a bodybuilder and very strong. It remains to be seen what the long term physiological effects will be on this child, but given his phenotype, there is talk of applications for muscular dystrophy i.e. compensating for the dystrophic effects by blocking myostatin production.

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Mammuthus
Member (Idle past 6475 days)
Posts: 3085
From: Munich, Germany
Joined: 08-09-2002


Message 88 of 248 (123931)
07-12-2004 11:53 AM
Reply to: Message 86 by arachnophilia
07-12-2004 10:53 AM


Re: lesbian lizards
Actually, I don't think it is such a problem. Just like bacteria and other asexual reproducing organisms, the lizards will still sustain mutations subject to selection. If asexual reproduction procluded evolution we would not see as much adaptation among bacteria as we do. However, they will be much slower to respond to change as sexual reproduction is much better at spreading variation than mistakes during clonal propagation...still strange stuff in any event.

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Mammuthus
Member (Idle past 6475 days)
Posts: 3085
From: Munich, Germany
Joined: 08-09-2002


Message 94 of 248 (124182)
07-13-2004 4:13 AM
Reply to: Message 89 by arachnophilia
07-12-2004 12:29 PM


Re: lesbian lizards
I certainly was not trying to imply that you sound like an idiot..hope it did not come across that way. The lizards are strange. Sexual reproduction confers such a benefit on a species that it has evolved multiple times in many varieties. Even bacteria are not true cloners...they exchange genetic information by horizontal gene transfer all the time which is sort of pseudo sexual reproduction. There are also really strange animals like the Daphnia species complex which can reproduce sexually, parthenogenetically, etc...they can really screw themselves if they want to Strange that a reptile would forgoe the benefit.

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Mammuthus
Member (Idle past 6475 days)
Posts: 3085
From: Munich, Germany
Joined: 08-09-2002


Message 97 of 248 (124411)
07-14-2004 5:19 AM
Reply to: Message 96 by Rrhain
07-14-2004 4:53 AM


Re: lesbian lizards
It is likely that sex was in their history as within the same genus, there are sexually reproducing whiptail lizards...strange why they gave it up...must have been a lousy dating scene
J Neuroendocrinol. 1995 Jul;7(7):567-76. Related Articles, Links
Species differences in estrogen receptor and progesterone receptor-mRNA expression in the brain of sexual and unisexual whiptail lizards.
Young LJ, Nag PK, Crews D.
Department of Zoology, University of Texas at Austin 78712, USA.
Circulating concentrations of gonadal steroid hormones and reproductive behavior in female vertebrates vary as a function of ovarian state. Steroids secreted by the ovary, specifically estrogen and progesterone, influence the expression of behaviors associated with reproduction by intracellular sex steroid receptors located in specific regions of the brain. Using in situ hybridization, we analyzed estrogen receptor and progesterone receptor messenger RNA expression in several brain regions of ovariectomized, vitellogenic, and postovulatory individuals from two species of whiptail lizards (Cnemidophorus uniparens and C. inornatus). Although these species are genetically very similar, they differ in two aspects of their reproductive biology: (i) the unisexual C. uniparens alternate between expressing female-typical and male-like pseudosexual behaviors while female C. inornatus normally express only female receptive behavior, and (ii) circulating estradiol concentrations in reproductively active female C. uniparens are approximately five-fold lower than in reproductively active female C. inornatus. We found that the regulation of sex steroid receptor gene expression was region specific, with receptor-mRNA expression being increased, unchanged, or decreased during vitellogenesis depending on the area. Furthermore, several species differences in the amount of sex steroid receptor-mRNA were found that may be relevant to the species differences in circulating estrogen concentrations and sexual behavior.

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