Let's talk about sex!

[Megatron]

Ok. Something that's probably been discussed before, but for the benefit of the dumbass (me), let's play a really cool game, I like to call it "Help Z_A (the dumbass) undertand why sexual reproduction evolved."

I'm assuming (mostly because of a complete lack of knowledge) that sexual reproduction, at one point, did not exist - i.e. when our 45098346587xGrandparents were single-cell organisms.

Evolution comes from a need for survival, and/or freak genetic mutations that just happen to be advantageous, correct?

Note: Bear with me guys, I'm a machine freak, I know nothing about biological science.

What made sexual reproduction evolve, and how was it advantageous enough for survival that it persisted (and still does, obviously, in millions - or is it billions? - of species) for millions of years? (Note: I say "millions of years" for lack of an exact figure, even though AFAIK the dinosaurs reproduced sexually... that's at least, what, 200M+ years ago?)

Let the game begin!

[sakrilege]

Real basic answer as to why sex survives, diversity in genetic material leads to greater survival advantage.

[Megatron]

Originally posted by sakrilege
Real basic answer as to why sex survives, diversity in genetic material leads to greater survival advantage. Hm.. that makes sense. Is there any good information on why/how/when it evolved? As in, what animals/plants/whatever it began with, and what the method was?

I mean, obviously, an asexual being didn't just suddenly spawn two offpsring with fully operative sex organs, and BANG, we have sex...?

[sakrilege]

Study Links Origin of Sexual Reproduction With High Mutation Rates (http://news.nationalgeographic.com/news/2001/07/0709_sexorigin.html)Claus Wilke of Caltech and Chris Adami, of both Caltech and JPL, have concluded that asexual bacteria can be nudged to evolve into sexual reproduction if they are subject to high levels of mutation induced by environmental stress?from, say, radiation exposure or a catastrophic meteor.

edited to add quote

[lpetrich]

I don't know what would be a good introduction to the variety of life cycles that organisms have.

It is instructive to look at how one-celled organisms reproduce.

Prokaryotes (bacteria) reproduce asexually, but they can squirt bits of genetic material into each other.

One-celled eukaryotes (protists) can reproduce either way, performing either conjugation (exchange of genetic material) or the meiosis/fusion cycle:

haploid - fusion - diploid - meiosis - haploid

As to what induced the evolution of sex, there has been a lot of speculation. A problem is that it dilutes one's genes, when asexual reproduction would result in no such dilution. A common speculation is that it's a way of speeding up evolution by instantly producing new genetic variants as a result of the recombination it induces. This may be possibly useful for out-evolving parasites, which sometimes mimic mechanisms inside of organisms.

[Corona688]

The way I read it, was it started when by some error or other, a cell split into FOUR cells instead of two. Each half-cell, or gamete, contained half the normal amount of genetic material. The four half-cells re-merged into two full cells. Thus, the cell had found a way to reproduce and shuffle it's genes at the same time. Do the same thing with two differing cells and bingo, sexual reproduction.

[lpetrich]

Alternatively, it started as a modification of conjugation, where two cells would fuse and then separate, with the resulting cells having a mixture of the genetic material of the parent cells.

Being mostly-haploid is the status of many fungi, but in many cases, the diploid phase changed from transient to persistent, with the haploid phase becoming transient in some cases.

[Calzaer]

I always thought that sexual reproduction as we know it was a requirement for reptiles to evolve for land-based living. Most marine life simply sprays sperm around with the hopes it'll hit an egg in the area. Frogs and other amphibians do the same thing, except the male is positioned such that he's RIGHT THERE as the eggs come out of the female - but the sperm still has to swim to the egg. On dry land, swimming to an egg isn't an option. That, combined with the amniotic egg (waterproof shell) developed so that critters could complete their reproductive cycle without a body of water nearby, necessitated internal fertilization.

[Megatron]

This may be true, but whether the fertilization is internal or external, there is still sexual reproduction involved...

See, the problem is, I had assumed that sexual reproduction had begun with complex life... I didn't know it was possible with single-cell organisms.

Hmm, this is some really good stuff. Thanks, guys! :)

[Ms. Siv]

Please read "The Red Queen" by Matt Ridley.

[lpetrich]

Calzaer:
I always thought that sexual reproduction as we know it was a requirement for reptiles to evolve for land-based living. ...
If you are referring to internal fertilization, that is completely correct. Not only animals, but also plants, perform it. Among conifers and angiosperms (flowering plants), a pollen grain grows a long, thin tube in search of an egg cell to fertilize.

[nessa20x]

Sexual reproduction does not mean there has to be internal fertilization. Coral, etc... still reproduces sexually even though it is not internal.

Sexual reproduction evolved because an increase in mixing of genetic information was favorable and increased the populations survival in some conditions. However it only is beneficial in certain situations. Some organisms make use of both sexual and asexual reproduction, utilizing the sexual repro when conditions are favorable...ie rapidly changing.

[Roland98]

Must've missed this before...but this is also more of an E/C topic.

-Roland98
S & S moderator

[pz]

Originally posted by Ms. Siv
Please read "The Red Queen" by Matt Ridley.
Yes -- an advantage of sex is that it randomizes traits, making it easier to keep ahead of parasites and disease.

Another thing to look up is "alternation of generations". Many organisms bounce back and forth between haploid and diploid states.

[lpetrich]

Plants have alternation of generations between a diploid "sporophyte" and a haploid "gametophyte" phase; these two phases have different appearances and sizes. In mosses, the gametophyte phase is more prominent, with the sporophyte phase growing on top of it, but in most other land plants, it is the sporophyte that is more prominent. In seed plants, the gametophytes are microscopic; male ones live in pollen grains, while female ones live inside of their parent plants. All the rest of the plant is sporophyte, a clear convergence on the typical animal-kingdom state of affairs, where the haploid phase is only the gametes.

Some organisms have a diploid or polyploid "zygospore" phase that is adapted for surviving relatively harsh conditions; when growing, they are haploid. This good-times-haploid, bad-times-diploid cycle is approximately converged on by aphids, which reproduce asexually during their hosts' growing seasons, and sexually at the end of those seasons.

This is consistent with the above hypothesis of what each phase is good for: in good times, make as many copies of oneself as one can, while in bad times, try to create new combinations of genes so one's offspring can have a chance of being better off.

[tronvillain]

Actually, I would definitely suggest reading the other Ridley's Mendel's Demon, though Matt Ridley's The Red Queen is quite good too. Best explanation of sex I have ever seen.

[rlogan]

The latest research points to alcohol.

Alcohol led to sex.

[arcangle]

Originally posted by Ms. Siv
Please read "The Red Queen" by Matt Ridley.

I had some very large problems with Ridley's Red Queen. Specifically:

"... free will was not created for fun; there was a reason that evolution handed our ancestors the ability to take initiatives, and the reason was that free will and initiative are means to satisfy ambition, to compete with fellow human beings, to deal with life's emergencies, and so eventually to be in a better position to reproduce and rear children than human beings who do not reproduce."

and further along:

"Human culture could be very much more varied and surprising that it is. Our closest relatives, the chimpanzees, live in promiscuous societies in which females seek as many sexual partners as possible and a male will kill the infants of strange females with whom he has not mated. There is no human society that remotely resembles this particular pattern. Why not? Because human nature is different from chimp nature."


I know that this post is probably off topic for this thread, and if someone with moderator-like powers would like to break it off, move it, rewrite it, whatever, that would be fine. I would just sincerely love to talk about the book in whatever forum the discussion belongs.


Lyn

[GunnerJ]

Best course of action (read: easist for me) would be for you to just make a new thread.

[arcangle]

Gotcha!

Thanks.


Lyn

[tronvillain]

I suppose I could wait for the thread, but what exactly are you problems with those quotes? I can see some debate about the first quote, but not the second.