Re: Cost of sex - a bargain!

On 16 Aug 2006 01:25:01 -0700,
Kent Paul Dolan <xanthian@xxxxxxxx> wrote:
Perplexed in Peoria wrote:
"Larry Moran" <lamoran@xxxxxxxxxxxxxxxxxxxxxxx> wrote:
Kent Paul Dolan <xanthian@xxxxxxxx> wrote:
Larry Moran wrote:

You are confused.

Perhaps, but you need to demonstrate that, not just
make an unsupported claim.

We don't know why sex is so common - that's why
it's considered one of the major problems in
biology.

Nonsense.

To extend that, it is nonsense to claim that we
_don't know_, biologically, why sex is common. We
know that perfectly well.

No "we" don't.

It is common because populations that reproduce
sexually can evolve much faster, and thus, as
populations, outcompete, for the same ecological
niches, both their closely related and only
distantly related competitors that reproduce
asexually.

You sound very sure of yourself. Have you tried to publish this?

A much better question is why _asexual_ reproduction
still exists at all, and quite possibly the current
issue under discussion, that the "cost of sex" is
so high, is the contrary directed force.

But "cost of sex" really does have to be "two for
one" advantageous to possibly counter the
evolutionary advantage forces which favor sexual
reproduction, and apparently, considering the number
of species that reproduce sexually, even that does
not suffice in many cases.

Are you aware of the fact that by mass and by total numbers (and possibly by
species) the majority of organisms on this planet reproduce mostly asexually?

My apologies, I though I was dealing with a
person who knew something about biology. I was
wrong.

You are wrong in thinking you know _anything_ about
my knowledge base in biology, just as you were wrong
in claiming that we _don't know_ why sexual
reproduction thrives under evolutionary pressure.

Who is this "we" that you're talking about?

Most knowledgeable evolutionary biologists consider sex to be one of the major
problems in biology. They do not know the answer.

Anyone who studies evolution discovers this very quickly. The fact that you
think you've solved the problem indicates that your knowledge of biology is
deficient.

Here's a recent paper on the subject of mixis from Aneil F. Agrawal at the
University of Toronto.

http://tinyurl.com/rpo9e

As you can see from the article, this is still very much an open question.
Here's the beginning of the discussion.

"The idea that genetic mixing could be advantageous if individuals
benefit from being different from their relatives is not new.
However, hypotheses based on this idea have been largely abandoned
for two reasons. First, these hypotheses were typically developed
within the framework of obligately sexual groups competing against
obligately asexual groups. Recently, there has been a shift away
from models based on group-level explanations for genetic mixing
[21,22]. Second, similarity selection is generally thought to be
much weaker than genotypic selection, and thus similarity selection
is presumed to be unimportant [23]. However, a proper analysis of
similarity selection using the modifier framework had been lacking."

Here's a recent review by S.P. Otto and A.C. Gerstein of the University of
British Columbia.

http://www.biochemsoctrans.org/bst/034/0519/bst0340519.htm

Why have sex? The population genetics of sex and recombination

"One of the greatest puzzles in evolutionary biology is the high
frequency of sexual reproduction and recombination. Given that
individuals surviving to reproductive age have genomes that
function in their current environment, why should they risk
shuffling their genes with those of another individual? Mathematical
models are especially important in developing predictions about
when sex and recombination can evolve, because it is difficult to
intuit the outcome of evolution with several interacting genes.
Interestingly, theoretical analyses have shown that it is often
quite difficult to identify conditions that favour the evolution
of high rates of sex and recombination. For example, fitness
interactions among genes (epistasis) can favour sex and
recombination but only if such interactions are negative, relatively
weak and not highly variable. One reason why an answer to the
paradox of sex has been so elusive is that our models have focused
unduly on populations that are infinite in size, unstructured and
isolated from other species. Yet most verbal theories for sex and
recombination consider a finite number of genotypes evolving in a
biologically and/or physically complex world. Here, we review
various hypotheses for why sex and recombination are so prevalent
and discuss theoretical results indicating which of these hypotheses
is most promising."

These scientists seem to be unaware of the fact that you have solved "one of
the greatest puzzles in evolutionary biology." Their reviewers must also be
ignorant. Perhaps you should let them know?

Populations that reproduce sexually are able to
evolve much(*) faster than populations that
reproduce asexually; crossover plus mutation is
massively more powerful than mutation alone.

I do evolutionary software as a hobby(**), I
prove this stuff to myself every time I vary the
proportion of mutation versus crossover per
reproductive event for a problem run.

Good for you. Carry on.

Permit me to try to extract and refine Larry's
argument from the raw ore of his putdowns.

Evidently, being "biologically knowledgeable" but
also innumerate, Larry isn't able to speak for
himself, so I'll answer you as his surrogate.

I don't pretend to be an expert but I know several experts and they seem to
think that sex is still a problem. I think I'll take their word over yours.

If you want to expand your knowledge of evolutionary biology I recommend
EVOLUTION (2005) by Douglas Futuyma. He has a discussion about "The problem
with sex" beginning on page 418. The first sentence is,

"The traditional explanation of the existence of recombination
and sex is that they increase the rate of adaptive evolution
of a species, either in a constant or a changing environment,
and thereby reduce the risk of extinction."

Futuyma then goes on to explain why this "traditional explanation" doesn't
solve the problem of sex. He points out that there are two main disadvantages
to sex and recombination. One is that recombination breaks up successful
combinations of alleles. The second is the cost of sex.

According to Futuyma, there are six hypotheses for the advantage of sex
and recombination but none of them are convincing. All six are described in
the textbook.

1. DNA repair
2. sibling competition
3. preventing mutational deterioration (Muller's Ratchet)
4. the mutational deterministic process
5. adaptation to fluctuating environments
6. enhanced adaptation under directional selection




Larry Moran

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Relevant Pages

  • Re: I got some major problems coming up wrt teaching evolution
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  • Re: I got some major problems coming up wrt teaching evolution
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  • Interrelation between Sex and Death
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  • Re: I got some major problems coming up wrt teaching evolution
    ... >>>say that sex remains one of the great mysteries of evolutionary biology? ... >>> them know the problem of sex will be solved. ... > is that recombination destroys adaptive combinations of genes. ... Yes, sex and gender has disadvantages, and it was one of the most ...
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