How exactly did sexual reproduction evolved?

[Cesrate]

One biology teacher said this question is still covered with mystery. So how much do we know about this part of evolution?

And why are there only asexual and bisexual creatures, not trisexual or others?

[Awaras]

Hey, animals (including humans too of course) have enough trouble finding ONE partner to reproduce with, imagine how much more difficult it would be to have to find two at the same time...

I guess the advantages of three sexes just aren't great enough to justify the increased difficulty of finding suitable partners.

Edited May 3, 2013 by Awaras

[Cesrate]

Hey, animals (including humans too of course) have enough trouble finding ONE partner to reproduce with, imagine how much more difficult it would be to have to find two at the same time...

Muti-sexual doesn't necessarily to be like this…

[Awaras]

Muti-sexual doesn't necessarily to be like this…

What do you mean then? Some sort of rock-paper-scissors combination?

[Person012345]

Well, I just woke up so I can't really explain in-depth for fear of saying something stupid and wrong, but it's to do with genetic diversity. If you only reproduce with yourself your genetic diversity in the population is low and this is not as good for surviving for various reasons. I imagine the reason there aren't 3-way creatures (or at least they aren't common) is that it's pretty much just unnecessary.

Although I think she's right in that it's not really resolved fully yet.

[Tommygun]

It's not really trisexual, but some frogs and I think some reptiles have the ability to change gender if there are not enough of the opposite sex around for most of a population to reproduce.

[Cesrate]

All right… Back to the most important question 1 please…

[Tommygun]

Well evolution works better when there are more mutations in the DNA.

There are just more chances of a useful mutation (bad mutations tend to die off).

So with two separate genders you get double the chances for a useful mutation.

This gives bisexual reproduction an advantage over asexual reproduction and I'm assuming this advantage is why more complex animals use this method as they out bred and out numbered other species that used asexual reproduction.

[Cesrate]

Well evolution works better when there are more mutations in the DNA.

There are just more chances of a useful mutation (bad mutations tend to die off).

So with two separate genders you get double the chances for a useful mutation.

This gives bisexual reproduction an advantage over asexual reproduction and I'm assuming this advantage is why more complex animals use this method as they out bred and out numbered other species that used asexual reproduction.

I know this, I would like to see possible detailed methods. I mean, in cellular biology.

[K^2]

This is a good starting point. In a nutshell, sexual reproduction is derived from sexual reproduction of a single celled eukaryote that is the common ancestor to all multicellular organisms. While it's not clear how or why that particular species gained that particular advantage, it is what allowed significantly faster evolution of its progeny, ultimately allowing for complex multicellular life.

[magnemoe]

Well, I just woke up so I can't really explain in-depth for fear of saying something stupid and wrong, but it's to do with genetic diversity. If you only reproduce with yourself your genetic diversity in the population is low and this is not as good for surviving for various reasons. I imagine the reason there aren't 3-way creatures (or at least they aren't common) is that it's pretty much just unnecessary.

Although I think she's right in that it's not really resolved fully yet.

yes three sexes don't bring any huge extra bonus, and will complicate stuff. Hard to imagine how it should work anyway. Would it require two sort of males and one female? More practical would be an system where all was bisexual or actual trisexual but required two different other partners.

Would probably require some dna like structure who used three ropes in the ladder, or rater the triangular structure would demand (dna) from three creatures.

Interesting idea, any other ideas how this could possible work?

Danger with an bisexual animal is that if it is able to inseminate itself this will have an short term benefit in that it could get many children but an long term risk that some disease or other change in conditions could whip it out as its has to lite variation.

[Nikolai]

I'm not a biologist, though I traded wedding vows with one. First of all, the division between sexual and asexual reproduction is kind of fuzzy. There are many algaes, mosses, and ferns that have generations that alternate between sexual and asexual reproduction. During the asexual generations, for example, ferns reproduce with spores; during the sexual generations, they reproduce with sperm released to swim to eggs in the (hopefully damp) soil. There are also single-celled organisms that swap genes, even though no distinct sexes exist. Perhaps one set of organisms evolved to transmit genetic information more efficiently than it received it, and another set of the same population evolved to receive more efficiently than it transmitted. If these differences snowball, perhaps they could give rise to different sexes.

AIUI, though, the actual evidence concerning how sexual reproduction arose is scant. It's not that there's doubt that it did evolve; the questions are aimed at figuring out how.

[Awaras]

yes three sexes don't bring any huge extra bonus, and will complicate stuff. Hard to imagine how it should work anyway. Would it require two sort of males and one female? More practical would be an system where all was bisexual or actual trisexual but required two different other partners.

Would probably require some dna like structure who used three ropes in the ladder, or rater the triangular structure would demand (dna) from three creatures.

Interesting idea, any other ideas how this could possible work?

Danger with an bisexual animal is that if it is able to inseminate itself this will have an short term benefit in that it could get many children but an long term risk that some disease or other change in conditions could whip it out as its has to lite variation.

You wouldn't need a triple-helix DNA to have three sexes. In our own reproduction, the male and female contribute half of the chromosomes, but each of those chromosomes are entirely from one or the other... All that would be necessary is for three sexes to contribute 1/3 of the chromosomes...

[K^2]

Not only that, but there are already plants with more than 2 copies of each chromosome. So in principle, these would have no trouble supporting more than 2 partners on the genetic level. Gamete production is also not that difficult. I am slightly concerned with gametes finding each other, though. If you need one of many sperm to find one of many eggs, that's one thing. If you need several different sperm to find the same egg? That's a whole different story.

But yeah, what it comes down to is that it's something that's very unlikely to evolve to begin with, and then doesn't really provide that much advantage over having just two partners. It's easy to imagine that a particular cell might end up having a genetic defect resulting in a mitosis before DNA replication step. That would produce two cells with half of the DNA. If each one can go dormant, then it's just a matter of two such cells bumping into each other and fusing again. The rest is just optimizing the process. Anything that would allow for more than 2 partners is a much more complex mutation.

[Moach]

if you take genetic programming as an analogue for such a thing (ignoring the massive irony in the comparison between sex as an evolutionary advantage to computer geekiness) the notion of coupling the best of two individuals to generate the fittest offspring seems to propose a possible 'convergence' scenario...

there are experiments on this type of thing that allows you to see the difference this 'feature' has on the results of an evolving system - actually, there's a clever little flash game that does that, here: http://boxcar2d.com/ (warning! you may just have been nerd-sniped)

it so could be, that having 2 sexes would maximize the benefits of natural selection vs the cost of physically mating said two individuals...

thus, the 'ease' of having each individual reproduce by itself does not outweigh the benefits of having two of them mix their own 'brew'

if you try and imagine a reduced scale setting, wherein mutation takes place in a dramatically accelerated pace, the chances that bad mutation will not stump further development are much higher if mating is a requirement for any given strand to continue...

without mating, evolution would come down to a lot of trial and error, and there are an infinite amount of things that can go wrong in that dangerous world out there...

the mating process is in itself a 'booster' for natural selection - if not for that, death would be the only factor to sort out the fit from the fodder

on the other hand, it does also appear that two genders may be an optimal number for such activities (though many people will not agree, albeit not for evolutionary reasons) - if you had more genders, it's even possible that mating could become so strict a selecting factor that the species would not be able to reproduce in numbers large enough to avoid being extinct...

there are, though, some select species (of beetles i think) that do have 3 genders... but i really don't know how that works - or even if this is really a fact and not something i perhaps misrecall

[MisterTelecaster]

OP, I feel like you should read Carl Sagan's Shadows of Forgotten Ancestors. You'd probably like it.

[metaphor]

Some bacteria can exchange genetic information between members of the same species. I think that's a starting point for the evolution of sexual reproduction (exchange genetic material for offspring, then eventually make specialized cells that do that, etc).

[Tommygun]

I wonder if you could draw a parallel between how viruses exchange DNA and how sexual reproduction started on a cellular level?

[Person012345]

Viruses aren't cells so I doubt it's the same.

[Tommygun]

But it does places it's DNA into a cell, not unlike how an egg gets fertilized and it can't reproduce without the cell.

[Paprika]

But it does places it's DNA into a cell, not unlike how an egg gets fertilized and it can't reproduce without the cell.

Depending on the virus, it can be extremely unlike how an egg gets fertilised.

Bacterial plasmid exchange by conjugation is a much better analogy/potential 'starting point' (so to speak), but even then there are huge differences.

[ialdabaoth]

There are some fungi with up to 8 different sexes, where each sex can reproduce with any of the other 7 (but not itself). I'll look up the specifics and come back...

[jason0735]

There are some fungi with up to 8 different sexes, where each sex can reproduce with any of the other 7 (but not itself). I'll look up the specifics and come back...

8 sexes would mean 7/8 of reproducing although it would be (Theoretically) Better than 1/2 it would cause much diversity in these 8 "Sexes".

[BigFatStupidHead]

Sex is quite an embarrassing subject for biologists, because we don't know why it evolved, and more importantly, we don't know why it is maintained. Sexual reproduction is a massive cost to the organism because they not only need to find mates, but half of their offspring (males) do not directly contribute to growing the population.

There are theories on why sex is maintained based on who you talk to. For example, parasitologists will point you to immunological models showing that more genetically diverse populations have greater resistance to, and smaller loads of parasites.

As for the mushrooms, they're known as mating types, rather than sexes.

[Dr. Muttonstache]

In a nutshell, sexual reproduction is derived from sexual reproduction of a single celled eukaryote that is the common ancestor to all multicellular organisms.

All I know is that I enjoy the outcome of what eukaroyte gave us.