Monday, November 16, 2009
Genetic Load
If the average rate of deleterious mutations is about 1 per individual per generation then the species can't survive. It means that most offspring will carry a mutation. This is an intolerable genetic load for a species.
In fact it's worse than that. Simple calculations suggest than even a rate of 0.1 deleterious mutations per individual will spell doom for the species. This is a well-known limitation and it was widely used in developing several key components of evolutionary theory and in explaining the size and composition of eukaryotic genomes.
The average total mutation rate in humans is about 130 mutations per genome per generation. Scordova concludes that this proves Intelligent Design Creationism [Nachman’s Paradox Defeats Darwinism and Dawkins’ Weasel]. It does no such thing. It proves once again that a little knowledge is a dangerous thing—especially in the mind of an IDiot.
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16 comments :
I've been discussing evolution with the bioengineers here at Caltech. Maybe not surprisingly, it turns out most of them are adaptationists.
I was wondering if you could recommend any good reviews/texts on evolutionary theory?
Thanks
How is the high mutation rate supposed to defeat "Darwinism," when ID (supposedly) predicts that most of the genome is functional and that mutations can only decrease information? IDiot indeed.
Come now Alexander, you're presuming that IDiots care about such trifles as evidence, facts, research, honesty, etc. They can't let such things get in the way of dogma, it might lead them into some sort of sin.
Actually, assuming conditions of synergistic epistasis, a deleterious mutation rate per genome per generation of 1 will favor sexual reproduction's ability to 'bulk purge' mutations via recombination and segregation over asexual reproduction... rather than the death of the species. However, why does God allow all of these deleterious mutations in the first place??? What kind of intelligent design is that?!?!?
This paragraph doesn't stand up unless you define "deleterious". How deleterious? Are we talking lethal? 50% reduction in fertility? 10%? 0.0001%? All of those possibilities are "deleterious", but the number of each you can tolerate will be radically different.
@Peter
In fact, no. Larry was discussing the fate of a species, not of an individual. The reduction in average fitness of a population is dependent on the mutation rate only. This is because mutations with a lower fitness cost are permitted to rise to higher frequencies. This is called the Haldane-Muller principle.
As is occuring too often Sandwalk leaves an interested outsider feeling left out of what is probably an interesting conversation. Larry and most of those commenting may be able to be happily knowledgeable and smirk at the IDiots ignorance. Me, I'm left wondering if this topic has something to do with neutral mutations and searching in vain for an explanation of the Haldane Muller principle. Guess what - I visit this and other blogs to get explanations of these things, not laughter at those who don't understand them with no explanation as to why they are wrong.
...and searching in vain for an explanation of the Haldane Muller principle.
As a teacher, I feel compelled to answer :-)
The idea is that in most species, there is a balance between the generation of new mutations on the one hand, and the removal of those mutations by natural selection on the other. Very deleterious mutations (lethals) have a huge fitness impact, but are almost instantly removed from the population. Very mildly deleterious mutations can persist for much longer. It turns out that these effects cancel out. The fitness reduction of the population due to mutational pressure (called the mutational load) is therefore independent of the fitness effects of the underlying mutations.
I'll leave it to Larry to explain the details. After all, he is a teacher too :-)
At first I thought you made a mistake in grammar when you wrote “ – a little knowledge is a dangerous things – especially in the minds of an IDiot.” I thought you should have used the singular “thing” and “mind”. But then I realized, IDiots are dualists! You wrote it right!
Carlo says,
... a deleterious mutation rate per genome per generation of 1 will favor sexual reproduction's ability to 'bulk purge' mutations via recombination and segregation over asexual reproduction... rather than the death of the species.
This is one of those ideas that seems superficially attractive. However, a little thought will reveal that the situation isn't so simple.
First, the "purging" via recombination only applies to deleterious mutations on the same chromosome. That restricts the advantage to only a small subset of all possible combinations.
Second, what recombination can put together, it can also take apart. Two deleterious mutations on the same chromosome can be eliminated simultaneously when the sperm or egg carrying them isn't chosen. However, recombination will separate those mutations so that they now reside on different chromosomes and this increases the probability that one of them will be passed on.
The advantage of recombination is measurable but it's only significant under very special conditions.
Finally, you can't select for future advantage and you can't select for the good of the species. The only way to select for enhanced sexual reproduction is if it benefits the individual and its ability to leave viable offspring.
Devin says,
I've been discussing evolution with the bioengineers here at Caltech.
That must be a frustrating experience. :-)
I was wondering if you could recommend any good reviews/texts on evolutionary theory?
The Futuyma textbook ("Evolution") is still the best one. The Gould and Lewontin "spandrels" paper should be required reading for everyone.
Chinahand says,
As is occuring too often Sandwalk leaves an interested outsider feeling left out of what is probably an interesting conversation.
Point taken. I'll try and explain it in another posting.
Anonymous says,
At first I thought you made a mistake in grammar ...
Thanks. I made the appropriate corrections.
Ah, scordova of "DNA steganography" fame.
For those old enough to remember, GM cars used to have little plates reading "Body by Fisher" on their door sills. scordova's idea was that Gawd left a leetle secret message (thus steganography) in human DNA stating "Body by Gawd," or something to that effect.
I would dearly love to be wealthy enough to leave a gazillion dollars to the Disco Institute on condition that they can use it only for the purpose of research equipment for a program aimed at finding scordova's secret steganographic message hidden in our DNA - no staff or admin salaries, no money for fancy offices, only for equipment for an absolutely futile purpose.
Or maybe a codicil that they can use the money for anything they want as soon as they take out a full page ad in the Sunday New York Times admitting that the whole DNA steganography thing is a crock?
What about compensatory mutations counteracting large genetic loads? Didn't Estes and Lynch publish a paper showing how some populations of C. elegans that had been mutationally degraded managed to recover full fitness in about 80 generations, and attributed those increases to compensatory mutations?
This is one of those ideas that seems superficially attractive. However, a little thought will reveal that the situation isn't so simple.
Actually, my comment was intended to be flippant, especially because there's little to no support for synergistic epistasis, and Kondrashov doesn't appear to believe his own theory in the first place anymore (at least he said so at the Sex and Rec conference in Iowa this summer). That's what I get for not thinking through my comments on Sandwalk...
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