Evolution of sexual reproduction

[dmehling]

I am looking for information on the evolution of sexual reproduction. I have recently come to realize what a novel and complex process this is, especially from an evolutionary standpoint. How is it that we have thousands or perhaps millions of species, each on their own unique evolutionary journey, with each species containing two sexes capable of breeding with each other? Each sex of a particular species has to have their own sexual reproductive systems and mechanisms evolve at the same rate as their counterpart and always remain sexually compatible. And this has to occur in every species as they continually change and evolve into new species. This sound like a very difficult process, but one I haven't heard discussed before. What is the best way of understanding that process?

[mith]

Each sex of a particular species has to have their own sexual reproductive systems and mechanisms evolve at the same rate as their counterpart and always remain sexually compatible. And this has to occur in every species as they continually change and evolve into new species. This sound like a very difficult process, but one I haven't heard discussed before. What is the best way of understanding that process?

Do you also believe multicellularity has to happen all at once?

[Eous]

yeast, single celled eukaryotes, can reproduce by replicating itself, or can switch to utilizing a mating type, with which it can mate with a yeast of the opposite mating type.

I'm sure this isn't the origin of mating types, but it helps to see that sexual reproduction does not require all of the advancements of higher multicellular eukaryotes.

[dmehling]

I have no idea.

[anaphase]

EWWWW, yeast effections suck. Sorry, just had too throw that out there.

[Darby]

A lot of sexual reproduction does not involve males and females, or separate individuals - neither of those are part of the basic definition.

The first evolutionary step was probably a polyploidy mutation - pairs of chromosomes instead of one. Or a weird plasmid production that made and shared the whole chromosome rather than just part of it.

[dmehling]

Again, I'm focused on creatures with distinctly male and female sexes, and how their means of reproduction evolved.

[robsabba]

Again, I'm focused on creatures with distinctly male and female sexes, and how their means of reproduction evolved.

From a situation where an individual was capable of producing both male and female reproductive structures (hermaphrodites, like many worms today) specialization evolved, where individuals produced only one or the other. In mammals (most vertebrates??) gender is determined by the sex chromosomes. The X is used by both genders, whereas X and Y are needed for the male. The Y is viewed as a deformed X chromosome and has much less information than the X. Presumably, the Y evolved from the X. Since males get one X chromosome, no information is lost in this process. If I made any incorrect assumptions here, someone please correct me.

[dmehling]

I still don't think you guys are really understanding my point. I'm not really asking how sexual reproduction originated or how it actually works. Rather I am interested in how sexual compatibility is maintained between the sexes of a species, as a species proceeds down a particular evolutionary path. Consider primates for example. They would have arisen from a single common ancestor. For a new species to develop (I'm assuming a species cannot interbreed with its parent species) would you not have to have simultaneous changes occurring in the reproductive systems of each sex? As you have these primates evolving into separate groups of humans, chimpanzees, gorillas, etc. there would have to be considerable evolution within each species since the biology of each sex is significantly different from its counterpart. Is there some kind of mechanism that would cause the reproductive systems of both sexes to undergo changes that are complementary to each other?

[Darby]

Genders are not separate species - they're just a set of differently- expressed genes amidst a multitude that work exactly the same way. And species arise from populations over time - the idea of a "common ancestor" doesn't really mean there was just one of them.

And once you get male-female genders (the basis of which is purely the types of gametes they make), all of the "rest" of the features still just serve the differences in the gametes.

[robsabba]

I still don't think you guys are really understanding my point. I'm not really asking how sexual reproduction originated or how it actually works. Rather I am interested in how sexual compatibility is maintained between the sexes of a species, as a species proceeds down a particular evolutionary path. Consider primates for example. They would have arisen from a single common ancestor. For a new species to develop (I'm assuming a species cannot interbreed with its parent species) would you not have to have simultaneous changes occurring in the reproductive systems of each sex? As you have these primates evolving into separate groups of humans, chimpanzees, gorillas, etc. there would have to be considerable evolution within each species since the biology of each sex is significantly different from its counterpart. Is there some kind of mechanism that would cause the reproductive systems of both sexes to undergo changes that are complementary to each other?

Remember that populations evolve, not individuals. Therefore, as the population evolves, compatability is automatically maintained. Any individual who cannot mate within the population simply does not pass on his/her genes. According to probability, any beneficial mutation is increased in the population over time, while detrimental mutations are kept at low levels.

[butterfly1]

Male and female compatability does evolve together.

I have read a lot of books by Matt Ridley that would help you to understand exactly how in great detail. The best one to read to answer your question would be 'The red Queen'. He details 'sexual selection theory' beautifully and uses a variety of species in order to clearly demonstrate the process.

Obviously an author can write much better than I but from what I can remember (I read the book about 3yrs ago now) sexual selection goes something like:

For example; The peahen chose the peacock for the elaborate and biggest tail feathers around at the time. His genes were therefore, passed on more readily and frequently than those peacocks with less elaboration and length of tail. In the next generation the same thing happened, until it became so elaborate and long that it was almost a disability to the peacock but this was not a priority over passing on his genes to the next generation.

If you already knew this gist of information and were specifically asking about male and female genitalia evolution then Matt Ridley's story went something like this:

Chimps have huge testicles in relation to their body size, whereas gorillas are tiny in proportion to their body mass. This is thought to be due to food. Gorillas find a food source and 'live' in it. Chimps have to keep moving around to find new areas of food. The Gorillas have stable monogamous relations with the females and chase off male sexual rivals. As he can sit quietly in abundance of food and not have to compete to have sex he doesn't have to fornicate very often to ensure passing on his genes and so his testicles do not have to produce as much sperm and so they have evolved in a small relative size. The chimp cannot keep such control over females as they often have to move to find food and on the way she might take the opportunity to fornicate with a rival. The chimps cannot chase off other males from the group because they are needed for protection of the whole group when they encounter predators on their travels. Thus, the chimp testicles are rather large for his body size because there is a lot more competition to pass on his genes so he must have sex exponentially more often than the gorilla to try to gain more chance of this happening.

'The Red Queen' illustrates this process in lots of other areas to, such as the species/disease arms race and I would highly recommend you read it