How does evolution account for the transition from asexual to sexual reproduction...?

Question

...within a species, and/or as a new species emerges?

a. If you think the theory of evolution can't account for it, please explain (nicely) why you think it can't.

b. If you think it the theory of evolution can account for it, please address, nicely, concerns raised in part a.

SecretSauce, I know a forum here where I could getcha plenty of material to try to refute in (a). But I thought I'd try it in this somewhat less volatile category first.

Bekki. You've caused me to chuckle with your "so bacteria that made a habit of it flourished. The rest of the development from there to mind-blowing sex is just evolutionary fine-tuning."

Is it indeed? Don't worry, because I consider mind-blowing sex to be satisfying on the spiritual as well as the physical level, I'd never ask you to try to trace evolution's path THAT far.

However, I was rather hoping the trail of evolution would get me to a level higher than single celled organisms (the complexity whose organelles, by the way, is often taken for granted) to get an explanation of what happens to Mrs. Cockroach for instance, when she says to not-yet Mr. Cockroach, "What the heck am I supposed to do with these eggs. Fertilize them meself? Hurry up--we have a species to...um start?"

I'll have to hunt down Red Queen. I hope it doesn't focus exclusively on WHY sexual reproduction might have had evolutionary advantages over asexual, the way other answers here have.

I want to know HOW species that existed already without sexual reproduction came to depend on sexes in one generation.

SecretSauce---Thanks for the interesting tidbit about Mrs. Feminist Aphid. I didn't know that. No wonder my rose bushes are swarming with them.

But here's MY point--I want to know how the species on the more specialized branches evolved from one another. In other words, how far back on the evolutionary tree must one back up from H.Sapiens before we find within a single species, multiple modes of reproduction?
Once a particular evolutionary branch becomes thoroughly specialized with respect to reproduction (ie--offspring iff mating between male and female of species occurs), how can the first species on this branch evolve into ANOTHER thoroughly reproductively specialized species, if a male AND female are required to produce offspring in this second species?

Are you telling me, then, that two mutant (and thus, uncharacteristically fertile) individuals from Species One, who are mutant in complementary ways, find each other happily at the same place and same time, and get it on?

Well Don, I went to talkorigins and found this excerpt from the court records of the 1st day of Kitzmiller vs. Dover Area School District. (Kitzmiller "A" defends the teaching of evolution.) "A:the evolution of sex is an enormous and controversial issue in biology.Q. Sex as in gender?A. Sex as in gender, as to why, for example, everybody does it, not just talking about us primates, but also oak trees and yeast and all sorts of organisms, as to where gender comes from in terms of sexual reproduction. It's a very important issue within evolutionary theory and certainly not an issue that is solved.There is also enormous controversy within evolutionary theory on the relative values and weights to give to forces such as natural selection, sexual selection, genetic horizontal gene transfer, and so forth."

Enormous Controversy sounds like there's a TON of "evolutionary fine tuning" vis a vis gender that's being accepted on FAITH--that observable microevolution PROVES evolution of species.

I'm going to go ahead and assign a best answer. SecretSauce, I think you tried hardest, even though your answer is still a long way from satisfying my curiosity. The problem lies with the evolutionary theory's limited ability to Explain All Creation, not with your lack of trying.

Answer 1

Well, I'll have to wait for somebody to weigh in with an answer to part a. before I can address (nicely) the concerns.

But I can point out that the transition from asexual to sexual was gradual, and there were many intermediate stages, all with examples that are still found in nature TODAY ... thus anticipating what I imagine will be the main objection by advocates of part a. ... namely that this was too big a jump.

These intermediate stages range from completely asexually reproducing organisms (some bacteria, plants, fungi, and some simple animals like sponges); to types of conjugating bacteria that co-mingle some DNA; to organisms that undergo both asexual and sexual reproduction (like aphids); to organisms that have both male and female organs in the same individuals (many flowering plants, occasional hermaphroditic animals); to organisms that go through a male stage and a female stage at some time in their development (various types of fishes); to organisms where males and females are determined by what they are fed during development (such as ants and bees); to organisms with dedicated males and females (most animals and some plants).

In all stages, co-mingling of genetic material from two individuals has an advantage in certain types of rapidly changing environments. Namely, it increases *variation*.

I.e. with asexual organisms, every individual is essentially a clone of its parent. It has the same exact genes, except for mutations. And thus, if there is some environmental crisis that starts to wipe out that organism, barring some lucky mutation, the crisis will wipe them all out. With sexual reproduction, every new individual has a different genotype than either of its parents. And thus there is a much larger chance of survivors of some environmental crisis.

{edit}

Heh. I know about that forum ... but that ain't no *science* forum.

As for Mrs. Cockroach ... try Mrs. Aphid instead. She can indeed say "no Mr. Aphid around ... I guess I *will* just fertilize 'em meself."

My key point is that it is a bit too black-and-white to imagine that there are just two forms of reproduction, asexual and sexual, and these require some "transition" between the two. Not only are there many, many different systems, but an individual species can use more than one system. E.g. species may display 95%-5% asexual vs. sexual phases. But it may gradually evolve to more of a 50-50 ratio in times of stress, or 90-10, or may lose the asexual phase altogether.

Nature mixes and matches very well ... we just happen to be on a branch that is very specialized (a feature I appreciate every time I experience that mind-blowing sex thing :-)).

Answer 2

Sexual reproduction alllows the mix of genes whereas asexual reproduction does not have genetic shuffling occur. As others have stated, sexual reproduction is usually better for evolution since it allows for genetic diversity and can result in an organism having a trait which will allow is to be better adapted for an environment, or fight off disease easier. Without sexual reproduciton, ever organism will be the same within a species, making it susceptible to environmental influences, and likely causing the loss of most, if not all, of the population. But asexual reproduction does have its uses. Asexual reproduciton is used when the environment has almost no chance of changing (like deep on the ocean floor). In this case, why should the organism change its DNA? If the environment is the same, with no chance of change, there is no point in spending a lot of energy in sexual reproduction. Asexual reproduction can also be a last ditch effort to save a species such as when the species is under stress (low shark populations). Recently, sharks in captivity have shown to undergo asexual reproduction, likely in response to environmental factors either in captivity or the wild.

Answer 3

Super simple answer:

The first sexual-type reproduction was probably just bacterial conjugation. Bacteria met and kind of fused for a bit and swapped genetic material. This has some potential survival benefits (explained in other answers), so bacteria that made a habit of it flourished. The rest of the development from there to mind-blowing sex is just evolutionary fine-tuning.

Many organisms (lots of plants) can reproduce both sexually and asexually, so the tools are there to adapt and use either strategy if evolutionary pressure pushes one way or the other.

Answer 4

Sexual reproduction is very old, and most species participate in some form or another. So it's likely that a new species that evolves will have evolved from a sexually-reproducing species, and thus won't need to evolve more than once. As to how it evolved, since the first sexually reproducing organism is almost certainly lost in the mists of time, we won't know. But the "why" is reasonably clear - sexually reproducing organisms are far more efficient at producing genetic variation, fixing beneficial variation and removing harmful variation via genetic recombination. As asexually reproducing organisms cannot recombine or mate, they do not gain the benefit of evolutionary innovations created in other members of their species.

Answer 5

Both are survival strategies - which work. Asexual reproduction actually has the advantage of preserving 100% of the genetic material in the next generation (if you subscribe to the selfish gene theory). Sexual reproduction generates variation, therefore providing a wider possibility of survivors (I didn't phrase that well but it's getting past my bedtime), again meaning there is more chance of your genetic material surviving.

Answer 6

Read Matt Ridley's book, 'The Red Queen'

Answer 7

It doesn't because evilution (lol) is not true. Ask God.