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Re: Rapid Lizard Evo

There were a few classic misconceptions in Dan's post I wanted to clarify: the majority of random mutations are niether harmful nor beneficial, most do not impact survival and reproductive success at all. Ones that do often have small impacts (e.g. a basepair substitution in a transcription promoter may make the protein may alter the affinity towards it's binding site, making a gene cascade turn on slightly sooner or later). These help rack up small phenotypic variations in general proportions which mostly don't matter but become selection-worthy when the environment changes (e.g. the larger heads of the lizards in the study under consideration).

Random mutations most certainly play a large roll in maintaining this type of overall phenotypic variation, and said variety is constantly acruing (albeit being weeded out too if the phenotype strays too far into contra-adaptive territory which provides the base variation that natural selection acts upon.

Dan is right that organisms that use sexual reproduction certainly leverage genetic recombination to increase the degree of phenotypic variation in a population (and in the case of strong selection it may also let a succesful trait proliferate more rapidly to the rest of the population). Also true that organisms with complex central nervous systems can buffer themselves against selection on their genomes by altering behavior, and this is especially succesful in organisms that can transmit learned behaviors.

It should be noted, however, that the vast majority of organisms cannot utilize one or both of these buffers, so the accumulation of random genetic variation into the genome still provides the majority of variation that is acted upon by selection in the history of life.

Scott Hartman
Science Director
Wyoming Dinosaur Center
110 Carter Ranch Rd.
Thermopolis, WY 82443
(800) 455-3466 ext. 230
Cell: (307) 921-8333


-----Original Message----- From: Dann Pigdon <dannj@alphalink.com.au> To: dinosaur@usc.edu Sent: Tue, 22 Apr 2008 5:23 pm Subject: Re: Rapid Lizard Evo

One of the worst generalisations about evolution is that it mostly involves random genetic mutations over long periods of time. I suspect that random mutation plays only a very small part in the evolutionary process, and that other processes (recombination, RNA interferance, learned behaviour, to name a few) provide far more fodder for natural selection to act on, and on a much smaller time scale. Â
Relying on random mutation is fine, as long as those mutations are actually beneficial (which most aren't), and as long as your environment doesn't change faster than *beneficial* random mutation can keep up with (which it almost certainly will). Otherwise you'd better have some short-term backup plans just in case. Â
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Dann PigdonÂ
GIS / Archaeologist http://geo_cities.com/dannsdinosaursÂ;
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