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Author Topic:   Asexual to sexual reproduction? How?
Wounded King
Member (Idle past 2174 days)
Posts: 4149
From: Edinburgh, Scotland
Joined: 04-09-2003


Message 16 of 78 (245750)
09-22-2005 2:33 PM
Reply to: Message 8 by Eledhan
09-22-2005 9:37 AM


Re: What?
You still must show how Natural Selection suddenly stops selecting, and then, continues selecting organisms further down the road.

An obvious explanation is that it doesn't, but what it selects for may vary over time. Some organisms routinely reproduce asexually but will reproduce sexually in response to an environmental stress.

TTFN,

WK


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EZscience
Member (Idle past 3233 days)
Posts: 961
From: A wheatfield in Kansas
Joined: 04-14-2005


Message 17 of 78 (245760)
09-22-2005 3:24 PM
Reply to: Message 15 by clpMINI
09-22-2005 2:18 PM


Re: Present day critters
clpMINI writes:

Zebra mussels are hermaphrodites...only takes one to tango.

Not exactly. A simultaneous herm cannot mate with itself - it needs a second individual. However, sperm are exchanged in both directions and eggs are fertilized in both individuals.

Simultaneous hermaphroditism seems to have evolved in species with very limited mobility in the adult stage. The advantage is that even if you only encounter one conspecific in your lifetime, sex will still be possible.

Hermaphroditism is a special case and really just one of the epiphenomena of sexuality.

Note also that sequential hermaphroditism (individuals changing from one sex to the other in their lifetime) is another special case and quite distinct from simultaneous hermaphroditism.

I do agree that extant examples of facultative sexuality can provide valuable insights into how and when sex is advantageous.


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EZscience
Member (Idle past 3233 days)
Posts: 961
From: A wheatfield in Kansas
Joined: 04-14-2005


Message 18 of 78 (245762)
09-22-2005 3:34 PM
Reply to: Message 8 by Eledhan
09-22-2005 9:37 AM


Re: What?
I don't think you really understand how natural selection can work.
For example, imagine a simple aquatic organism that produces propagules capable of parthenogenetic development (no sex). In some cases these propagules might fuse with otherS OF the same species prior to initiating development. Assuming the diploid offspring SO produced had higher fitness than the haploid (parthenogentically produced) offspring, you could have selection for sexual reproduction. Initially, organisms would not have to abandon asexual reproduction and the population would consist of a mixture of both haploid and diploid individuals, although only the haploid ones would be able to reproduce sexually. The tricky part is the subsequent evolution of a mechanism to restore the haploid state to germ line cells so that diploid individuals could then also reproduce sexually. This is what meiosis does in all sexual individuals today.
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Cal
Inactive Member


Message 19 of 78 (245763)
09-22-2005 3:37 PM
Reply to: Message 14 by EZscience
09-22-2005 1:48 PM


Red Queen
Is anyone familiar with the 'Red Queen' theory?

I thought it was the "Red Queen Hypothesis", actually, but, yes. In fact, I'm just now reading Matt (aka "not Mark") Ridley's book, The Red Queen. (Last week, I read Mark (aka "not Matt") Ridley's, The Cooperative Gene, which makes a fairly convincing argument for sexual reproduction as an error-correcting mechanism).

But I'm still fuzzy on who exactly it was that first invoked the Red Queen metaphor. Wasn't it Leigh Van Valen?

Aphids are fascinating. Basically born pregnant like the tribbles in the old Star Trek episode, aren't they? Anyone ever looked at exploiting them as a food source?

ETA: tags, but while I'm at it, "ready to breed" would have been better than "pregnant", I suppose.

This message has been edited by Cal, 09-22-2005 03:49 PM

This message has been edited by Cal, 09-23-2005 09:22 AM


This message is a reply to:
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EZscience
Member (Idle past 3233 days)
Posts: 961
From: A wheatfield in Kansas
Joined: 04-14-2005


Message 20 of 78 (245773)
09-22-2005 4:38 PM
Reply to: Message 19 by Cal
09-22-2005 3:37 PM


Re: Red Queen
Cal writes:

I thought it was the "Red Queen Hypothesis"


Yes, quite correct. My carelessness.

Cal writes:

But I'm still fuzzy on who exactly it was that first invoked the Red Queen metaphor

It was Graham Bell in his 1982 book.
I actually had him as a supervisor of an undergrad thesis project I did at McGill Univ. back in the 70's.

Cal writes:

"ready to breed" would have been better than "pregnant", I suppose

Actually, that's exactly what I call sometimes it when I lecture on aphids. Tony Dixon would call it the 'telescoping of generations'. Each nymph actually has embryos developing within it at birth, so you essentially have 3 generations represented in a single individual !


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RAZD
Member
Posts: 19758
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 5.8


Message 21 of 78 (245799)
09-22-2005 6:48 PM
Reply to: Message 9 by Eledhan
09-22-2005 9:45 AM


Re: Silly Design...
Eledhan, msg 9 writes:

... but I figured I would just try to rebutt the comment RAZD made about Silly Design relating to this current topic.

Unfortunately you didn't rebutt anything, all you did was make an argument from incredulity followed by an unsubstantiated assertion with no evidentiary basis, and a non-sequitur to boot.

I hope you don't think that sex was a silly thing to design ...

It could have been a serious design and it could have been a silly design, that is part of looking at both sides of the design question. When I look at the design elements, though, I have to admit that my impression is that the way it is implemented fits Silly Design Theory better than Neo-Paleyanism (often called "Intelligent" design).

Now, if you wish to try to refute the concept, please demonstrate that sex is sensible to the point of distraction and that no jokes have ever been made about this behavior. Then we can discuss the rational behind all the sex toys ... and related behavior.

Just for starters.

Or you can wait to see the research by the Silly Design Institute into this matter.

P.S. I realize that this is not really related to the topic ...

But if you are going to dismiss evolution as a process to develop sex, then you are left with either creationism (god created animals that way) or some form of design theory.

"God did it" is unprovable, so the only argument left then is some form of design theory, and when you compare both sides of the design question you will see that Silly Design Theory makes much more sense than Neo-Paleyanism in relation to the actual evidence of not just species but behavior.

{added "neo-" to distinguish this new version from previous ones, although the sum scientific contribution in the interim period is sadly lacking in content}

This message has been edited by RAZD, 09*22*2005 07:03 PM


we are limited in our ability to understand
by our ability to understand

RebelAAmerican.Zen[Deist
... to learn ... to think ... to live ... to laugh ...
to share.


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RAZD
Member
Posts: 19758
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 5.8


Message 22 of 78 (245803)
09-22-2005 7:18 PM
Reply to: Message 19 by Cal
09-22-2005 3:37 PM


Re: Red Queen
Anyone ever looked at exploiting them as a food source?

Ants do. They have aphid farms, and milk them for their 'honey'


we are limited in our ability to understand
by our ability to understand

RebelAAmerican.Zen[Deist
... to learn ... to think ... to live ... to laugh ...
to share.


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 Message 19 by Cal, posted 09-22-2005 3:37 PM Cal has responded

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Dr Jack
Member (Idle past 184 days)
Posts: 3507
From: Leicester, England
Joined: 07-14-2003


Message 23 of 78 (245868)
09-23-2005 4:35 AM
Reply to: Message 17 by EZscience
09-22-2005 3:24 PM


Re: Present day critters
Not exactly. A simultaneous herm cannot mate with itself - it needs a second individual. However, sperm are exchanged in both directions and eggs are fertilized in both individuals.

Not always. Earthworms, for example, will mate with themselves if they fail to locate a suitable mate. I believe this behaviour occurs in a number of other haermaphroditic species.


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Cal
Inactive Member


Message 24 of 78 (245911)
09-23-2005 9:58 AM
Reply to: Message 22 by RAZD
09-22-2005 7:18 PM


Food source
Anyone ever looked at exploiting them as a food source?

Ants do. They have aphid farms, and milk them for their 'honey'

Speaking of food sources, in some gall midges, the larvae are not only able to produce larvae parthenogenically (without fertilization) and paedogenetically (before they reach adult stage), but while they're at it, they consume their mother from the inside out.
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Dr Jack
Member (Idle past 184 days)
Posts: 3507
From: Leicester, England
Joined: 07-14-2003


Message 25 of 78 (245913)
09-23-2005 10:11 AM
Reply to: Message 24 by Cal
09-23-2005 9:58 AM


Re: Food source
There's a species of tree frog which lives in pools of water high in the branches of the rain forest. Trouble is the frogs are carnivorous and the only food source in algae - so they create a load tadpoles which eat the algae for them, and then eat the tadpoles.
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AdminJar
Inactive Member


Message 26 of 78 (365434)
11-22-2006 2:53 PM


Bump for Archer.
As you command sir. Also did you get my email? If so please catch me in chat.
  
Dr Adequate
Member
Posts: 16085
Joined: 07-20-2006
Member Rating: 10.0


Message 27 of 78 (365456)
11-22-2006 4:11 PM
Reply to: Message 1 by Eledhan
09-20-2005 11:04 AM


I made this up

Yes, that's the problem.

There, I've said it. Now I would like to hear if my example is flawed in any way.

I can barely see any way in which it is not flawed. So far as I can see, there are two true statements in it:

"there must be a genetic mutation in the gene pool."

"this mutation must be beneficial."

The rest of it is stuff you've made up.

Edited by Dr Adequate, : No reason given.


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Hawks
Member (Idle past 4226 days)
Posts: 41
Joined: 08-20-2006


Message 28 of 78 (365522)
11-22-2006 10:34 PM
Reply to: Message 1 by Eledhan
09-20-2005 11:04 AM


Take it to Michael Behe
I take it that this is some sort of irreducible complexity kind of argument. You know, the one where there are so many interdependent parts needed that evolution could not possibly have done it. From your opening post it would seem that this is how you view things. But as several others have pointed out, everything leading from asexual to fully sexual reproduction (male and female) would not have happened in one generation. There would have been a precession of changes taken place over multiple generations. (BTW, You should not have dissed Mr Jack's imaginitive suggestions so easily. There was simply an attempt to show you HYPOTHETICALLY how this could have happened.).

The reasoning in your opening post was flawed, but even IF your statements were valid, they might not necessarily be a huge problem. In fact, points 3-8 could in fact be fulfilled by the organism in which that one original mutation occurred, simply splitting in two as per usual and then mating with itself. Boom, more progeny and more potential mates (but then, just like you did in your original post, I'm just rambling here).


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platypus
Member (Idle past 3833 days)
Posts: 139
Joined: 11-12-2006


Message 29 of 78 (365533)
11-23-2006 1:22 AM
Reply to: Message 8 by Eledhan
09-22-2005 9:37 AM


Re: What?
This post has been pretty well covered, but I would just like to add to the responses of two of the questions.

quote:
If sexual reproduction is "better", then why is the most effecient reproducing organism bacterium?

quote:
Don't you think it's kind of odd that an organism wasting energy on supporting a sexual reproductive system would be able to survive?

Size places many interesting constraints on physiology. What is most "efficient" for a bacteria is not necessarily more "efficient" for an elephant. Also, accept for a second that it is more beneficial to be a bigger bacteria. Sexual selection may be more costly than asexual selection, but it allows for bigger sizes to be attained. If the advantage to being bigger outways the disadvantages of sexual reproduction, then we will see sexual reproduction evolve as a result of natural selection, even though it is not neccessarily beneficial in itself to be a sexual reproducer.

As an additional point, let me grimace and invoke Dawkins. If selection happens on a genetic level and not an individual level, then we must ask a new question. Is it advantageous for a gene to propogate through sexual reproduction? If it is, as some previous messages on this thread have suggested, then natural selection would favor sexual genes over asexual genes, regardless of the cost to an individual. (Note- my feelings about this argument are mixed, but its out there.)


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Hyroglyphx
Member
Posts: 5622
From: Austin, TX
Joined: 05-03-2006


Message 30 of 78 (365628)
11-23-2006 4:10 PM


Difficult to resolve
Lets suppose that the earliest components for life did arrive by chance and that explaining how they got their was inconsequential. The prevailing theory about evolution asserts that simple organisms first proliferated by asexual reproduction -- a self-replicator. Why then would nature select new organisms that had to mate, one male, and one female in order to do that which is much more difficult to achieve, as far as survival is concerned, if nature, in fact, selects the most optimal organism?

Let's think of it on the individual basis first.

The organism that first evolved sex organs must have had those glands in place in order to produce offspring. What does that organism also need in order for it to pass on its genetic material? It needs a suitor of the opposite sex. A host of organisms from a certain population had to basically devolve from asexual reproduction but had to now evolve both a male and a female, virtually simultaneously, with all of their sexual organs intact just to proliferate sexual reproduction, much less, to have the population survive. That's inconcievable!

What kind of staggering odds would it be for a population of asexual organisms to evolve two separate, but compatible sexes, simultaneously in order to create the sex glands perfectly operable in a male, and also simultaneously evolve a female partner for the male with all of her sex organs in perfect operation? And again, why would nature select this over asexual reproduction? Its inconcievable.

You can call that an argument of incredulity, but I call it an argument from sensibility. These are the finer aspects of what evolution would have to have entailed in order to propagate. It just doesn't seem to add up. Am I missing some critical information?


Faith is not a pathetic sentiment, but robust, vigorous confidence built on the fact that God is holy love. You cannot see Him just now, you cannot fully understand what He's doing, but you know that you know Him." -Oswald Chambers
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