Sex Is Not About Promoting Genetic Variation, Researchers Argue

Atheistextremist
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Sex Is Not About Promoting Genetic Variation, Researchers Argue

 

 

ScienceDaily (July 7, 2011) — Biology textbooks maintain that the main function of sex is to promote genetic diversity. But Henry Heng, Ph.D., associate professor in WSU's Center for Molecular Medicine and Genetics, says that's not the case.

 

Heng and fellow researcher Root Gorelick, Ph.D., associate professor at Carleton University in Canada, propose that although diversity may result from a combination of genes, the primary function of sex is not about promoting diversity. Rather, it's about keeping the genome context -- an organism's complete collection of genes arranged by chromosome composition and topology -- as unchanged as possible, thereby maintaining a species' identity. This surprising analysis has been published as a cover article in a recent issue of the journal Evolution.

"If sex was merely for increasing genetic diversity, it would not have evolved in the first place," said Heng. This is because asexual reproduction -- in which only one parent is needed to procreate -- leads to higher rates of genetic diversity than sex.

For nearly 130 years, traditional perceptions hold that asexual reproduction generates clone-like offspring and sexual reproduction leads to more diverse offspring. "In reality, however, the relationship is quite the opposite," said Heng.

And not only does asexual reproduction lead to higher rates of genetic diversity, it also is two times more efficient than sexual reproduction.

In fact, two billion years ago in Earth's biosphere, life relied exclusively on asexual reproduction, and every organism was capable of bearing young without costly competition to mate. With asexual species' faster and more efficient mode of reproduction, the origin and maintenance of sex -- not exactly the fittest means of reproduction -- puzzles scientists, who for decades have been asking, Why has sex evolved and survived?

Although many scientists have offered answers to this question, most have focused on the benefit of mixing or purifying genes. But by taking the genome theory into account, Heng's findings may have dethroned the queen of problems in evolutionary biology.

According to Heng, the hidden advantage sex has over asexual reproduction is that it constrains macroevolution -- evolution at the genome level -- to allow a species' identity to survive. In other words, it prevents "Species A" from morphing into "Species B." Meanwhile, it also allows for microevolution -- evolution at the gene level -- to allow members of the species to adapt to the environment.

Considering their observations and those of paleontologists, population geneticists and ecologists cited in the article, Heng and Gorelick argue that new research should focus on the genome, not just the individual genes, because the genome serves as both the genetic information unit and selection package for evolution.

http://www.sciencedaily.com/releases/2011/07/110707161037.htm

 

 

"Experiments are the only means of knowledge at our disposal. The rest is poetry, imagination." Max Planck


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 That's very interesting,

 That's very interesting, and it does make sense to a certain degree.  I'm trying to think in terms of evolutionary advantage.  If species A evolves offspring species B and species A proves inferior and dies out, how would preserving the species be beneficial?  Why would such a mechanism survive?  It seems a bit redundant.  Also, the whole definition of species revolves around ability to exchange genetic information, that would seem of little advantage to asexual plants for example.  It would seem that preserving the species would segue as an advantage only after sex has come into play.  Just my two cents. 

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Here is my prediction: This

Here is my prediction: This guy's hypothesis will be shredded to bits in about 1 week, by at least two prominent scientists. Today is July 7, 2011. I'm giving him till July 14, 11:59pm.

Quote:
"If sex was merely for increasing genetic diversity, it would not have evolved in the first place," said Heng. This is because asexual reproduction -- in which only one parent is needed to procreate -- leads to higher rates of genetic diversity than sex.

Complete bollocks. He doesn't say a single thing about the parasite co-evolution hypothesis. Methinks he doesn't know what the fuck he's talking about.

Quote:
But by taking the genome theory into account, Heng's findings may have dethroned the queen of problems in evolutionary biology.

More complete bollocks. 'Genome theory'? Pfft. What genome theory? This guy sounds a bit like a quack. And shame on Science Daily for sensationalizing shit like this.

Quote:
According to Heng, the hidden advantage sex has over asexual reproduction is that it constrains macroevolution -- evolution at the genome level -- to allow a species' identity to survive. In other words, it prevents "Species A" from morphing into "Species B." Meanwhile, it also allows for microevolution -- evolution at the gene level -- to allow members of the species to adapt to the environment.

Man, this is tired old shit. It was blown out of the water by Dawkins in 1976, The Selfish Gene. (The actual theory is prior to Dawkins. He just formulates it into an excellent metaphor that is easily understood by non-scientists, without requiring in-depth understanding of statistics.)

The old 'good of the species' garbage. Not even as sophisticated as group selection. I'll be very surprised if Carleton gives the guy tenure, and I hope this isn't the sign of some trend there.

[Edit: Oops, I misread that. Apparently Heng is with Wayne State, and Gorelick is at Carleton. Still. Yuck.]

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Evolution/Sex

Evolution/Sex and Asexual reproduction was touched on pretty heavily in Matt Ridley's book, The Red Queen Theory. A pretty extensive book on the subject and highly reccomended for anyone that is interested in sex and evolution. Not saying that ALL of his theories were correct, but they were quite fascinating.

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What a curious name to grow up with...

Atheistextremist wrote:

 

Dr. Heng and fellow researcher, Root Gorelick, Ph.D., associate professor at Carleton University in Canada, propose that.... 

 

 

 

"Experiments are the only means of knowledge at our disposal. The rest is poetry, imagination." Max Planck


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An important function of sex

An important function of sex is to allow evolution to 'work', by allowing a single potentially beneficial mutation to spread through a population.

The equivalent function in single-cell organisms which reproduce by fission is by direct exchange of genetic material. While fission alone would spread the genes, exchange actually keeps the species together as an evolving unit, so actually, like sex, it promotes the opposite of diversity, by continually mixing the genes together across the group.

Species without such mechanisms would not 'evolve' anywhere near as effectively, which is precisely why sex and "bacterial conjugation" exist. Those without it were simply be left behind.

It allows more combinations of genes to be tested by natural selection, while maintaining a better degree of coherence as a species when mutations occur.

Promoting evolution is not the same as promoting 'genetic diversity' at all.

IOW it promotes the evolution of the genome, rather than just individual genes.

Dunno if I've quite expressed it correctly, but what they are trying to say seems to me to just not quite 'get it'.

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Atheistextremist

Atheistextremist wrote:

 

 
ScienceDaily (July 7, 2011) — Biology textbooks maintain that the main function of sex is to promote genetic diversity. But Henry Heng, Ph.D., associate professor in WSU's Center for Molecular Medicine and Genetics, says that's not the case.

 
Heng and fellow researcher Root Gorelick, Ph.D., associate professor at Carleton University in Canada, propose that although diversity may result from a combination of genes, the primary function of sex is not about promoting diversity. Rather, it's about keeping the genome context -- an organism's complete collection of genes arranged by chromosome composition and topology -- as unchanged as possible, thereby maintaining a species' identity. This surprising analysis has been published as a cover article in a recent issue of the journal Evolution.

As soon as people start using rhetoric like 'function', 'purpose', 'reasons'...it smacks of ad hoc reasoning, and begins to traverse into the realms of Creationsim and ID, instead of using non polarized terms like 'byproduct', 'resulting in', 'the effects of which are'...

FFS, it 'is' what 'it is'.

 

I keep asking myself " Are they just playin' stupid, or are they just plain stupid?..."

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BobSpence1 wrote:An

BobSpence1 wrote:

An important function of sex is to allow evolution to 'work', by allowing a single potentially beneficial mutation to spread through a population.

The equivalent function in single-cell organisms which reproduce by fission is by direct exchange of genetic material. While fission alone would spread the genes, exchange actually keeps the species together as an evolving unit, so actually, like sex, it promotes the opposite of diversity, by continually mixing the genes together across the group.

Ah. Okay, I can sorta see where they are trying to go now, at least. But it still does not do what the Science Daily article says it does (and, I've noted, other lame science columns have automatically published this barely-more-than-a-sensationalist-press-release).

The pure-asexual reproduction model would be like a branching tree whose limbs never reconnect with each other, and so, you end up with far more leaves (different varieties) than you would with recombination, and hence the claim of greater genetic diversity for asexual reproduction. They are almost certainly right on that score.

But they do not address the parasite co-evolution hypothesis, which requires recombination to maintain genetic variation between individuals within a local population.

Using the tree analogy: Even though the asexual organisms will have trees with more branches and leaves, those leaves which exist nearby each other still look like nearly identical clones. Only the leaves on relatively distant branches are going to look very different. On the other hand, in sexual organisms, two parent branches will make a bunch of child leaves, and each one will be substantially different from the others, and indeed from the parents themselves. In fact, there's only about 50% genetic similarity between closely related individuals. This local genetic diversity probably exists as a defense against parasitic infections: If Dad is prone to the lethal Toe Worm, but only passes on this trait to half his kids, then you won't see whole villages of people wiped out by rapidly spreading Toe Worm epidemics. Whereas if the entire village is made of clones of Dad, and 99% of them inherit Toe Worm susceptibility, then village goes bye bye at the first site of a Toe Worm.

(Toe Worms don't really exist, but I was trying to think up something nasty. Can you imagine a Toe Worm getting into your shoe? Yuck! Eye-wink )

Probably I should read the article before blaming the sensationalism on the researchers, but the quotes in the article are pretty damning, if they are accurate.

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 A recent Indiana

 A recent Indiana University Study supportd the Red Queen Hypothesis. They used a species of worm that is capable of reproducing either asexually or sexually. In an aseptic environment, asexual reproduction was predominant. When the researchers added a stressor to the environment ( a parasite), asexual reproducers died out. Sexual reproduction allowed the worms to maintain resistance to the parasite. Sexual reproducers thrived.

 

This would support the idea that sexual reporduction promoted disease resistance, ie INCREASED variation. But I think it is more than just increase variation. It is that specific variations were propagated through the species allowing for mass resistance to the parasite. 

 

This is as close to god as nature is gonna get. Sexual reporoduction allows for variation that is not entirely random. It is...dare I say...intelligent variation. Of course, it is intellegent only because it is mathematically more effiicient than random variation and therefore, has been maintained in the system of life. It does kind of make you see how easy it is to leap to the idea of a designer.

 

The designer is mathematics. 


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FlorenceHamilton wrote: A

FlorenceHamilton wrote:

 A recent Indiana University Study supportd the Red Queen Hypothesis. They used a species of worm that is capable of reproducing either asexually or sexually. In an aseptic environment, asexual reproduction was predominant. When the researchers added a stressor to the environment ( a parasite), asexual reproducers died out. Sexual reproduction allowed the worms to maintain resistance to the parasite. Sexual reproducers thrived.

Interesting. Thanks for the find.

Quote:
This would support the idea that sexual reporduction promoted disease resistance, ie INCREASED variation. But I think it is more than just increase variation. It is that specific variations were propagated through the species allowing for mass resistance to the parasite.

Hmmm. I'm more partial to the idea that sexual reproduction leads to increased local variation, and so parasites have a harder time adapting to their OWN environment (their sexually reproducing hosts) because it is constantly shifting underneath them, rather than being a uniform field of green (asexually reproducing 'clone' hosts).

For example, in a population of humans, a particular viral or bacterial disease (or a worm or what have you) may reproduce millions (or hundreds, for worms and such) of times more frequently than humans reproduce. As such, a population of human clones would be wiped out by a disease in much less time than even a single generation.

However, because we reproduce sexually, there is just too much variation in our populations, and so while variant A of the disease might be able to infect 5% of the population, variant B can't improve on that number, because only 5% of the population is susceptible to the infection mechanism of the parasite/pathogen. And the other 95% of the population is made up of different groups, some susceptible to variant C, and some to variant D while being immune to B and A, etc.

But all of this happens in a single generation of humans. The variation is already there.

It's not the case that sexual reproduction saves us in this situation because it helps us spread particular variations. It's simply that it promotes variations of all kinds, which makes it really hard for parasites to home in on the "Achilles Heel" that all humans have. Each human has different Achilles Heels already, and different immunities already. It's that overall variation that inhibits parasites from wiping out whole populations.

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