For three sexes to come together to make a baby (assuming their genetics were an extension of our model) they’d need to have triplets of homologous chromosomes, not triple-stranded DNA. I don’t know of any reason that something like that couldn’t evolve on earth, especially since there are triploid plants. It would make meiosis pretty complicated, thought.
This rings a bell with me, the female was a blueish “cloud” and the mail was a triangle or something no? And the third one was egg-shaped… I am thinking it was a “book in book”, in that it was described in some other work of fiction. At the same time I am getting little ringing bells about the guy who wrote “Planet of the Apes”…
Holy shit, I sound like that guy on Crossing Over or whatever it’s called.
There was an Asimov short story featuring 3 sexes. Two of the sexes were referred to with masculine pronouns (he, his, him) and the remaining sex with feminine pronouns. I think their sex names were adjectives like Emotional, Parental, and Rational or something like that.
Oh, good show AHunter3! 
It’s in the Gold collection if anyone can find their copy, I sure can’t. Dunno where I got the stuff about Planet of the Apes tho… thanks for saving my sanity!
Whenever the subject turns to weird biology, I always turn to the fungi. A quick Google of “mating type” led me to Coprinus cinereus, which has at least four different sexes.
Now, the first thing to know about fungal sex is that they mate in pairs just like everyone else. However, members of one sex, or rather mating type, cannot mate with members of the same mating type. Any other mating type will do, however. Think about it, instead there being a 50% chance that you will be able to mate with any other random individual, with four sexes, the odds increase to 75%.
Protists also offer numerous opportunities to examine unusual mating systems. The common Paramecium has eight mating types, although according to this page, P. caudatum has sixteen.
Well, you could make a case for it being time-lapse mutualism, in historic terms at least: the fetus lives off the mother for nine months and depends on her for nutrition for an extended period thereafter – as the mother enters old age and the offspring comes to maturity, the mother then lives off the largesse of the offspring. Just another bit of sociobiology…
In our class for the Monterey bay aquairum, there is a 12 sex item, I forgot which, perhaps a tapeworm? Female Cleaner fish can change their sex in a few hours.
The single-celled Parameciam amelia has eight different sexes.
Actually, it was a 1972 novel written by Asimov entitled “The Gods Themselves.” It won several awards, including a Hugo and a Nebula.
I was wondering if anyone was going to bring it up…
Chlamydomonas (no, it’s an alga, not the cause of chlamydia) has ten sexes. None of them are “male” or “female” as we generally understand the terms. Instead, there is an interlocking set of possible matings. Many bacteria also have sexes, although they are quite capable of fissile reproduction. Again, “male” and “female” really aren’t valid categories, more “donor” and “acceptor”, but the status can change, and some species are simultaneously both “donor” and “acceptor”. To make matters even more complicated, some bacteria are able to viably exchange DNA across species, and there is evidence that some bacteriophages actually can perform a “parasexual” function by transmitting bacterial genes from strain to strain.
Now, the bacterial system is pretty simple and flexible. But it’s pretty costly for individuals–they only do it if severely starved. If your population runs into the trillions, it’s fine. The 10-sex method is very complex, and a given individual might never run into a compatible conspecific.
So, many multicellular species ended up with two sexes. A smaller number ended up hermaphroditic, and a very small group are parthenogenic/cloners. Parthenogenesis is far more common among plants than animals. One very common example is the dandelion. Yes, bees do visit them, but they are, nevertheless, apomictic.
you guys ever notice that as the thread gets longer and longer, the posts get longer too?
I’m surprised no one has mentioned this, despite it’s obvious lack of utility in the thread
In Plato’s Symposium, one of the drunken guests (Aristophanes, IIRC, although not neccessarily the dramatist) describes that state of affairs at the beginning of time: there was one gender of humans; it was combination of female and male (not exactly hermaphroditic). The combination gender had four hands, four feet, two heads, and two faces. When it wanted to go somewhere quickly, it would roll.
One day, this…rolling person…thing decided to try and reach heaven. They began climbing Mt. Olympus when Zeus saw what they were trying to do. In anger, he throw a lightning bolt and split the “person” in two, thus creating man and woman. Man and woman then hugged desperately for a long time, wishing to be rejoined. One day, one of them died (I can’t remember which; probably woman as they never fare to well in fables) and the other went out to seek another woman, so he could have someone to whom he could wish to be rejoined. Thus, as the story goes, love was born.
Uh, yeah. Bear in mind Aristophanes was drunk when he told this story. Regardless, I think it’s cute. Kind of disturbing, but cute.
I know it doesn’t help, but it amuses friends at parties.
–greenphan
It’s actually two different questions as to whether there are/were more than two parents for a given offspring, or whether there are/were more than two mutually exclusive groups you could choose the parents from.
In Earthly biology, each parent contributes one chromosome (NOT one strand of DNA). Most creatures on the planet have either single or double chromosomes, but many plants have quadruple or more. So there’s no physical reason you couldn’t have more than two parents, giving a child with triple or more chromosomes. However, I don’t think such a system has ever evolved here. I imagine that the added benefit of adding more variation in your child is very small compared to the hassle of finding yet another appropriate mate (think about the number of personal ad sections you’d need!).
However, there’s no reason to only have two sexes. In fact, you don’t need them at all. You could let any individual mate with any other individual (leaving aside the question of who’s going to change the diapers). But mating with someone genetically similar is kind of a waste of time, so you want to make sure your potential mate is at least a little different, genetically. So different genetically determined groups arise, that only mate with individuals not in that group. No reason to have just two groups, and many species have lots of them. In fact, among the millions of species of bacteria (who don’t really mate, but do exchange genetic information), I imagine you could find just about every rule you can imagine regarding number of strains and who exchanges with who – only two strains, or twenty five, each of which can only exchange with between 7 and 15 of the other strains (for example). Kind of like astrological signs, I guess. (“hey, baby, what’s your strain?”).
But once your species gets to the point where someone has to make a great big egg (rather than everyone just dumping their genetic material into a big pile and letting the kid sort itself out), and then change diapers and get gum out of the brat’s hair for twenty years, it makes sense to link this role to one mating strain. Once that happens, it’s easy to show that you’re going to end up with two and only two sexes – those who put in the investment in the kids and those who don’t.
Which isn’t to say of course that males can’t make any contribution to their child’s welfare (some have even been known to change diapers).
Well, sure. The weight of the thread stretches them out while you’re writing your reply. Once you hit the Submit button, it rolls back up again, and they stay stretched out.
Great summary, Quercus, except for one nit:
You mean each parent contributes one set of chromosomes. Humans, for example have a double set of 2n=46 chromosomes. When meiosis[sup]Google it yourself![/sup] occurs to produce the sperm and egg, this reduces the number back to a single set, n=23. When sperm fertilizes egg, the number is restored to 46.
As you said, the normal chromosomal state of most organisms that people are familiar with is 2n. Others, like fungi, turn the whole thing around and are normally n. Some plants go in the opposite direction. The potato, for example, is 4n.