Why sex?

| 19 Comments

Continuing my springtime frolicsome mood, a paper in this week's Nature shows that sex is good for us. Well, not necessarily us as individuals, but as a population. This has actually been a longstanding argument in evolutionary biology—sex is risky, it's hard work, and it is prone to failure. Why not just have women reproduce asexually, and bloom into pregnancy automatically as soon as they hit puberty? That would be much more efficient. Sex also has the problem of breaking up good gene combinations; as you may or may not know, my wife is perfect, but in order to reproduce, she has to water down her flawless genes by combining them with those of a lesser member of the species, me. And then of course, there's the problem of us males. We could instantly double the reproductive capacity of our population if all males were equipped with uteruses and could also bear children. It's a weird, weird system.

So why do we bother with sex? Why aren't we being displaced right now by more fecund asexual populations?

Continue reading "Why sex?" (on Pharyngula)

19 Comments

Now that is cool. Like most students, I guess, I had just assumed that the advantage of sexual reproduction was to increase the range of combinations from which to select. I was nonplussed when I heard a talk by Matthew Meselson in which he disclosed that there was no empirical evidence to back that up. One small editorial recommendation: For the benefit of our creationist evoskeptics, the seemingly tiny advantage per mitotic division doesn’t just add up; it increases multiplicatively (exponentially?). So, especially if you allow for more than 6000 years of biological history, the advantage can become enormous.

By the way, has anyone read the book by Lynn Margulis and Dorion Sagan - something like “Three Billion Years of Sex”? Sounded interesting, but I haven’t gotten around to it.

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Why aren’t we being displaced right now by more fecund asexual populations?

To paraphrase Leo Szilard, “They are among us but call themselves dandelions.”

You would agree with this hypothesis if you saw my lawn.

That’s all good, and I’m glad that what was expected has been confirmed.

But let’s not forget another apparently quite important role that sex plays, which is simply weeding out deleterious genes in slowly reproducing populations, like ourselves. So while our mitochondria tend to accumulate mutations due to a lack of recombination, accumulated nuclear DNA damage typically is less, since damaged DNA is remixed with undamaged DNA in the sexual reproduction cycle.

Most mitochondrial DNA is thought to have “migrated into” (actually, such migrations were selected after the fact) the nucleus under just such selective pressures. The little that is left is thought to be a disproportionate source of genetic disease.

It’s another case of poor “design” in any design scenario, and just another fact of evolution in the realm of real science.

This doesn’t detract from the crucial importance of showing the adaptive capacities provided by sex. I just wanted to flesh the picture out more for anyone not familiar with common evolutionary ideas about sex.

Why not?

My own views on sex are somewhat different. Sexual reproduction has evolved independently many times. For that reason alone it cannot be considered fudamental to evolutionary change. Quite the contrary, all tangible evidence indicates that sexual reproduction is quite incapable of supporting macroevolution. So far it has not even been demonstrated to support true speciation.

I have suggested that a primary role for obligatory sexual reproduction is to stabilize the species, allowing small adjustments to a reasonably stable environment but incapable of weathering dramatic alterations. In short, sexual reproduction is and has been anti-evolutionary. Its failure to support evolution is evident right now as thousands of species are disappearing annually while none are replacing them.

Furthermore, if it were not for the limitations of sexual reproduction there never could have been any evolution. Extinction was a mandatory feature allowing the next higher taxonomic unit to flourish.

There is no reason whatsoever to believe that progressive evolution is occurring today and every reason to believe that evolution, like the development of the individual has been a self-termination phenomenon. In my studied opinion, sexual reproduction has been that self-terminating instrument.

John A. Davison

My own views on sex are somewhat different. Sexual reproduction has evolved independently many times. For that reason alone it cannot be considered fudamental to evolutionary change. Quite the contrary, all tangible evidence indicates that sexual reproduction is quite incapable of supporting macroevolution. So far it has not even been demonstrated to support true speciation.

I have suggested that a primary role for obligatory sexual reproduction is to stabilize the species, allowing small adjustments to a reasonably stable environment but incapable of weathering dramatic alterations. In short, sexual reproduction is and has been anti-evolutionary. Its failure to support evolution is evident right now as thousands of species are disappearing annually while none are replacing them.

Furthermore, if it were not for the limitations of sexual reproduction there never could have been any evolution. Extinction was a mandatory feature allowing the next higher taxonomic unit to flourish.

There is no reason whatsoever to believe that progressive evolution is occurring today and every reason to believe that evolution, like the development of the individual has been a self-termination phenomenon. In my studied opinion, sexual reproduction has been that self-terminating instrument.

John A. Davison

“Quite the contrary, all tangible evidence indicates that sexual reproduction is quite incapable of supporting macroevolution.”

Dr. Davison, can you provide references for this evidence? Preferably something more recent than Empedocles.

“Its (sexual reproduction) failure to support evolution is evident right now as thousands of species are disappearing annually while none are replacing them.”

Several mass extinctions have occurred in the past. Each was closely followed by rapid speciation in which newly evolved species, many employing sexual reproduction, filled newly opened niches.

“Furthermore, if it were not for the limitations of sexual reproduction there never could have been any evolution.”

Species that reproduce asexually don’t evolve?

“In my studied opinion, sexual reproduction has been that self-terminating instrument.”

When do you plan to publish the research (lab or field) that supports this conjecture?

My views and the support for them have already been published. My papers are available online and in the libraries of the world. Just plug in Davison and evolution on Google. You will find them I am sure. My nost recent anti-Darwinian heresy is “A Prescribed Evolutionary Hypothesis” which can be found without the figure at ARN, “brainstorms” and EvC. It will appear in the next issue of Rivista di Biologia sometime this summer.

Species that reproduce mitotically probably do not evolve as you say. There are other forms of asexual reproduction that generate plenty of genetic and chromosomal structural diversity. I refer you to my Manifesto for the details. I am not prepared to present all that evidence here at this time. It is a touch of your mouse away.

John A. Davison

I’ve read your “A Prescribed Evolutionary Hypothesis” Dr Davison. It’s conjecture supported by reference to archaic authority. You’re paid as a biologist. Can’t you think of some way to empirically test your hypothesis? If your hypothesis is untestable it has little worth as a scientific hypothesis.

Not mentioned much around here, but I think the work of John Endler is appropriate for this discussion. pbs even has a nice little online “game” that uses some of his work:

http://www.pbs.org/wgbh/evolution/s[…]ndwidth.html

you can see a list of his publications here:

http://www.jcu.edu.au/school/tbiol/[…]f/endler.htm

I studied under him when i was an undergrad at UCSB, about 20 years ago.

one of the very best evolutionary biologists i ever had the priviledge to meet.

JAD is a fraud! check out my theory about him over here:

http://www.pandasthumb.org/pt-archi[…].html#c23906

I think it makes more sense that believing what he posts truly reflects his thinking.

cheers

I don’t think he’s a fraud, though I did enjoy your reasons for stating so. I think he’s a sad unfortunate man who found himself in a field with a central idea that he found threatening to his belief in God. Cognitive dissonance has interesting effects. In Dr. Davison’s case it led him to try to disprove the theory of evolution. He has persuaded himself that he has indeed disproven this evil. He’s amazed that the rest of the world, or even the members of his own college, fails to understand and acknowledge his genius.

Has anyone here actually met JAD face to face?

:S I try to stay away from unstable trolls. You want pictures of him? His web site has one.

Personally I’d say just don’t read his posts. Sinse I started filtering out his posts this site has returned to one of my favorite blogs to read and participate in.

well, not that i would dimiss anyone’s commentary out of hand normally, but i feel i’ve flogged the dead horse that is JAD as much as necessary to satisfy my own morbid curiosity.

How do you filter posts on this board?

cheers

for that matter, how does one register to utilize post edit and spam features?

:S Sorry I browse PT with a custom VB app I’ve writen. If you really want the source to it you can email me.

If I get time, work is a #$*&@ right now, I wouldn’t mind doing some work for Reed. That and I thought it would be cool to port my app to a firefox plugin … but don’t hold your breath for the 2nd one.

Sorry if this is a dbl post.

:S Sorry I use a custom vb app I wrote to read/listen to PT. Thats how I filter. If you want it you can email me for the source but you’ll need VB6 to compile it.

If work ever slows down I would like to do some programming for Reed. I’ve thought about porting my app to a Firefox pluggin to…would be interesting but don’t hold your breath on it.

well, the board could certainly use some work. slow response times and server errors included.

cheers

p.s. I’ll take you up on your app offer, if you would be so kind. Could you send me the compiled version? the email i attached to my handle works fine.

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This page contains a single entry by PZ Myers published on March 31, 2005 9:35 AM.

Nature: Biologists snub ‘kangaroo court’ for Darwin was the previous entry in this blog.

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