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Why We Have Sex: It's Cleansing
LiveScience.com ^ | 3/2/06 | Ker Than

Posted on 03/02/2006 2:12:21 PM PST by anymouse

Scientists have long wondered why organisms bother with sexual reproduction. It makes a whole lot more sense to just have a bunch of females that can clone themselves, which is how asexual reproduction works.

Turns out sex might have evolved as a way to concentrate lots of harmful mutations into individual organisms so they could be easily weeded out by natural selection, a new computer model suggests.

The classic explanation for the onset of whoopee, about 1 billion years ago, is that it provides a way for organisms to swap and shuffle genes and to create offspring with new gene combinations that might survive if the environment suddenly changes.

But some scientists think this isn't enough of a justification to outweigh the many costs of getting together to make little ones. Just ask any single person—sexual organisms have to spend valuable time and resources finding and attracting mates.

If all organisms were like starfishes and cacti, which just drop pieces of themselves when they want to multiply, reproduction would be a whole lot simpler. There would be no need for elaborate peacock feathers or bird songs; stags wouldn't need antlers; elephant bulls wouldn't have to produce stinky cologne and guys probably wouldn't spend so much money on dates.

Natural cleansing

The new work could help test a hypothesis first proposed nearly 20 years ago, stating that sex evolved as a way to purge harmful mutations from a population. According to this view, the random shuffling of genes through sex will sometimes have the effect of concentrating many harmful mutations into single individuals.

These individuals will be less healthy than their peers, and therefore more likely to be weeded out by natural selection, the thinking goes.

This hypothesis, called the "mutational deterministic hypothesis," is controversial though, because it assumes that single mutations by themselves are only slightly harmful, while a combination of many mutations together is much more damaging. Scientists call this phenomenon "negative epistasis."

If negative epistasis were true, it would provide a powerful explanation for why sex has managed to persist for so long despite its numerous costs. But the phenomenon has yet to be widely demonstrated in nature and scientists have yet to figure out how such a thing evolved in the first place.

A new computer model by Ricardo Azevedo of the University of Houston and colleagues provides a possible answer to this last question. According to their model, detailed in the March 2 issue of the journal Nature, negative epistasis is a natural byproduct of sex itself.

Digital critters

The researchers created digital organisms that reproduced through sex in the same manner as real organisms. And like a regular organism, the virtual one developed a natural buffer to resist change by mutations. This ability, called "genetic robustness," is thought to be one of the main benefits of sex.

By shuffling genes, sex allows a population to spread its mutations across many individuals within a group. The mutations become diluted and can be effectively dealt with by an individual's genetic repair system.

But the researchers found that the protection only works when the digital organisms were facing a few mutations at a time. When assaulted by many at once, their repair systems became overwhelmed and the organisms died. Azevedo think this happens in real life, too.

"Most organisms are never forced to adapt to being resistant to many mutations at once," he told LiveScience. "They're adapting to being resistant to one or maybe two mutations, but not to ten at the same time."

The researchers think that the combination of genetic robustness through sex and the limited ability of organisms to deal with mutations leads to the natural development of negative epistasis.

"Most mutations are actually harmful, so anything that helps populations get rid of their harmful mutations is going to be important," Azevedo said. "The more interesting side of evolution is all the beneficial mutations that leads to complex structures, but the dirty work of evolution is to get rid of bad mutations, and that's where sex seems to play a role."


TOPICS:
KEYWORDS: biology; computer; computermodeling; crevolist; data; datamodeling; environment; evolution; genetics; metadata; model; mutation; science; sex
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I guess we'll need a shower after this thread gets going. ;)
1 posted on 03/02/2006 2:12:25 PM PST by anymouse
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To: Bender2

I'm sure you will have some inappropriate comments for this thread. :)


2 posted on 03/02/2006 2:13:32 PM PST by anymouse
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To: anymouse

That's as good as an excuse as any.


3 posted on 03/02/2006 2:14:32 PM PST by ShadowDancer (No autopsy, no foul.)
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To: anymouse
The new work could help test a hypothesis first proposed nearly 20 years ago, stating that sex evolved as a way to purge harmful mutations from a population.

Good thing I'm in my 40's.

4 posted on 03/02/2006 2:15:02 PM PST by Tijeras_Slim
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To: anymouse
This writer has it absolutely wrong. Sex was invented to keep women in their place.

[ducks to avoid frying pan]

5 posted on 03/02/2006 2:15:36 PM PST by Zuben Elgenubi
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To: anymouse

Or as my ex-wife would say "Why have sex"


6 posted on 03/02/2006 2:15:43 PM PST by UB355
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To: anymouse

Somehow I always seem to feel a bit dirty afterwards...


7 posted on 03/02/2006 2:15:56 PM PST by corkoman
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To: anymouse
...concentrating many harmful mutations into single individuals...

That is why the homosexuals should not be married.

Leave them single so they can fulfill their function.

8 posted on 03/02/2006 2:16:29 PM PST by Dan(9698)
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To: anymouse
Hey, baby, in the mood for a little negative epistasis tonight?
9 posted on 03/02/2006 2:17:59 PM PST by colorado tanker (We need more "chicken-bleep Democrats" in the Senate!)
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To: Dan(9698)

In case you hadn't noticed, sex isn't just happening between married people. Kind of screws up your theory.


10 posted on 03/02/2006 2:18:03 PM PST by ShadowDancer (No autopsy, no foul.)
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To: corkoman

You must be doing it right...


11 posted on 03/02/2006 2:18:18 PM PST by mouse_35
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To: Zuben Elgenubi
Sex was invented to keep women in their place.

In charge?

12 posted on 03/02/2006 2:18:47 PM PST by Tijeras_Slim
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To: anymouse

"Hey Honey, wanna get clean?"


13 posted on 03/02/2006 2:19:04 PM PST by D.P.Roberts
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To: Tijeras_Slim

Hehehe...

That says a lot!


14 posted on 03/02/2006 2:19:12 PM PST by Hoodlum91 (pcottraux says I'm special!)
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To: anymouse
"Most mutations are actually harmful, so anything that helps populations get rid of their harmful mutations is going to be important,"

I've heard of some hokey pickup lines in my time but this one takes the cake.

15 posted on 03/02/2006 2:20:02 PM PST by Billthedrill
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To: ShadowDancer; Dashing Dasher; Millie

Over here, folks.

My theory: Female microorganisms foresaw the advent of the VCRs and oil changes and needed to evolve an organism with at least a modicum of analytical ability.


16 posted on 03/02/2006 2:20:05 PM PST by Larry Lucido
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To: anymouse
Turns out sex might have evolved as a way to concentrate lots of harmful mutations into individual organ

Correction. ... might have been designed as a way ...

17 posted on 03/02/2006 2:20:17 PM PST by plain talk
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To: anymouse
According to their model, detailed in the March 2 issue of the journal Nature, negative epistasis is a natural byproduct of sex itself.

Computer model... sounds reasonable.

18 posted on 03/02/2006 2:21:10 PM PST by steveo (There is absolutely nothing like the MAIN-frame of a dame....)
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To: Tijeras_Slim; Zuben Elgenubi
In charge?

ROTFLMAO!!!

19 posted on 03/02/2006 2:21:13 PM PST by demkicker (democrats and terrorists are familiar bedfellows)
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To: anymouse
This hypothesis, called the "mutational deterministic hypothesis," is controversial though, because it assumes that single mutations by themselves are only slightly harmful, while a combination of many mutations together is much more damaging. Scientists call this phenomenon "negative epistasis."

If negative epistasis were true, it would provide a powerful explanation for why sex has managed to persist for so long despite its numerous costs. But the phenomenon has yet to be widely demonstrated in nature and scientists have yet to figure out how such a thing evolved in the first place.

-----

a new computer model, cool.. this many help explain carville and matlin,, bill and hil and webb

some may well be pre-disposed to breed themselves out of existence. Good old Mother Nature.

20 posted on 03/02/2006 2:21:15 PM PST by NormsRevenge (Semper Fi ... Monthly Donor spoken Here. Go to ... https://secure.freerepublic.com/donate/)
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To: PatrickHenry

VR sex ping!


21 posted on 03/02/2006 2:21:57 PM PST by AntiGuv
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To: anymouse

Soon as I get my graduate degree I'll come back and read it again and maybe understand it. :)


22 posted on 03/02/2006 2:22:39 PM PST by jazusamo (:Gregory was riled while Hume smiled:)
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To: Hoodlum91
If you just reproduced asexually your entire population would be very similar and therefore at risk for being completely wiped out by disease, environment change, or a better species. This really isn't news.
23 posted on 03/02/2006 2:23:02 PM PST by RHINO369
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To: Millee
You know, after reading this I realize you're right. It is boring.
24 posted on 03/02/2006 2:23:13 PM PST by Mike Bates (Irish Alzheimer's victim: I only remember the grudges.)
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To: anymouse

Oh goody! Now I know what to do with my "special purpose".


25 posted on 03/02/2006 2:23:35 PM PST by jslade (Liberalism ALWAYS accomplishes the exact opposite of it's stated intent!)
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What a bunch of ridiculous nonsense.


26 posted on 03/02/2006 2:23:42 PM PST by GretchenM (What does it profit a man to gain the whole world and lose his soul? Please meet my friend, Jesus.)
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To: anymouse

More evolutionist speculation and general hooey to explain the obvious presence of design throughout all creation.


27 posted on 03/02/2006 2:25:06 PM PST by Elpasser
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To: anymouse

You're not fully clean until you're sex fully clean.


28 posted on 03/02/2006 2:25:11 PM PST by wolfman
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To: anymouse
What have you 2 been up to???

http://www.whysanity.net/muppets/mimages/bunsen.gif

29 posted on 03/02/2006 2:26:12 PM PST by wallcrawlr (http://www.bionicear.com)
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To: Zuben Elgenubi

Invented to keep women in their place? Huh? Guys are the ones that can't go two seconds without thinking about it! We women can't seem to get you guys to leave us alone!
You don't see us women cruising the streets for a good time for twenty bucks! :P


30 posted on 03/02/2006 2:26:47 PM PST by derllak
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To: Tijeras_Slim

LOL. Good one.


31 posted on 03/02/2006 2:27:12 PM PST by Zuben Elgenubi
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To: anymouse
According to this view, the random shuffling of genes through sex will sometimes have the effect of concentrating many harmful mutations into single individuals.

These individuals will be less healthy than their peers, and therefore more likely to be weeded out by natural selection, the thinking goes.

...Except that that this process doesn't weed out the bad genes. The genes are still present in the organism's siblings. Of course, not all of the siblings have all of the bad genes, but they do share quite a few and they can pass those genes along to the next generation.

32 posted on 03/02/2006 2:28:04 PM PST by Redcloak (<--- Not always a "people person")
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To: corkoman

I 'fake' it.


33 posted on 03/02/2006 2:28:35 PM PST by johnny7 (“Iuventus stultorum magister”)
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To: derllak

What can I say? We love to be clean!


34 posted on 03/02/2006 2:28:52 PM PST by Zuben Elgenubi
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To: anymouse
Why We Have Sex: It's Cleansing

Not if you do it right.

SD

35 posted on 03/02/2006 2:29:01 PM PST by SoothingDave
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To: Larry Lucido
Female microorganisms foresaw the advent of the VCRs and oil changes...

And jars with lids.

36 posted on 03/02/2006 2:29:05 PM PST by PaulJ
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To: RHINO369

"If you just reproduced asexually your entire population would be very similar and therefore at risk for being completely wiped out by disease, environment change, or a better species. "

Theoretically. However, that doesn't explain how the simplest life forms continue to exist since they reproduce asexually. Not only to they exist, they develop mutations so the population continues to exist. I think you're short-changing asexual reproduction.


37 posted on 03/02/2006 2:29:25 PM PST by Hoodlum91 (pcottraux says I'm special!)
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To: anymouse
"The classic explanation for the onset of whoopee, about 1 billion years ago, is that it provides a way for organisms to swap and shuffle genes and to create offspring with new gene combinations that might survive if the environment suddenly changes."
Certain things must be adhered to at all cost.
38 posted on 03/02/2006 2:30:05 PM PST by Marine_Uncle (Honor must be earned)
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To: Larry Lucido

You weren't really expecting me to respond to that, right?


39 posted on 03/02/2006 2:30:05 PM PST by ShadowDancer (No autopsy, no foul.)
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To: Zuben Elgenubi

I'll get back to you - as soon as I locate my frying pan!


40 posted on 03/02/2006 2:30:55 PM PST by derllak
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To: anymouse

HOw about this hypothesis - Sex has survived for so long because it feels so damn good!!!!


41 posted on 03/02/2006 2:31:38 PM PST by commish (Freedom Tastes Sweetest to Those Who Have Fought to Preserve It)
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To: Tijeras_Slim

"In charge?"

You got that right.


42 posted on 03/02/2006 2:32:15 PM PST by Warren_Piece (Smart is easy. Good is hard.)
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To: anymouse

Article has several flaws:
1. Sexual reprodution has no survival advantage over non-sexual reprodution. In fact, in a desert, the cactus may be the best survivor.
2. The article bases its 'coup-de-grace' (spelling?) on a computer model. A computer model is only as good as the program. And do any of us REALLY know all the variables that go into this complex phenomenon, so as to be able to put it into a program?


43 posted on 03/02/2006 2:32:25 PM PST by razoroccam (Then in the name of Allah, they will let loose the Germs of War (http://www.booksurge.com))
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To: commish

http://www.forbes.com/2003/10/08/cz_af_1008health_print.html


44 posted on 03/02/2006 2:32:41 PM PST by Howlin ("Quick, he's bleeding! Is there a <strike>doctor</strike> reporter in the house?")
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To: Mike Bates

And here I thought you pinged me to this because my pic finally made it through. Sigh..


45 posted on 03/02/2006 2:32:50 PM PST by Millee (Don't make me get out my voodoo doll out!)
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To: ShadowDancer

Well, I did make sure I was 20 miles away from you when I posted.


46 posted on 03/02/2006 2:34:04 PM PST by Larry Lucido
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To: anymouse; mad puppy
I guess we'll need a shower after this thread gets going. ;)

Here is a shower mate for you!


47 posted on 03/02/2006 2:34:29 PM PST by SirChas (I seem to be rapidly approaching the apex of my mediocre career)
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To: anymouse

"but the dirty work of evolution is to get rid of bad mutations, and that's where sex seems to play a role."



Now if THAT doesn't get you in the mood...


48 posted on 03/02/2006 2:35:03 PM PST by SE Mom (God Bless those who serve..)
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To: plain talk
Correction. ... might have been designed as a way ...

Certainly the language of the explanation in the article is more appropriate to the actions of a designer than to a set of natural processes.

49 posted on 03/02/2006 2:35:07 PM PST by r9etb
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To: Millee

I thought that was supposed to be a secret, but if not. . . .


50 posted on 03/02/2006 2:36:50 PM PST by Mike Bates (Irish Alzheimer's victim: I only remember the grudges.)
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