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Reproduction and Sex
Posted: Posted June 27th, 2007 by eldin raigmore
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First, see the following threads in http://listserv.brown.edu/archives/.
LISTSERV.BROWN.EDU ( CONLANG: )



Item # Date Time Lines Subject
126275 2005-07-06 14:00 476 THEORY: Language for a Multi-Species Society: Sex-Based Genders Among Neuters, Hermaphrodites, and Sex-Changers.

126325 2005-07-09 17:04 453 Re: THEORY: Language for a Multi-Species Society: Sex-Based Genders Among Neuter


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REALISTIC BIOLOGY
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There are species on Earth whose reproduction is sexual and which have more than two sexes; but each particular individual just has two parents.

It is not always the case among Earth species that an individual's two parents have unequal roles. If the parents' roles are equal, it may be difficult or impossible or unnecessary to decide which parent is its mother and which is its father.

When the parents' roles are unequal, on Earth, the following three things tend to go together (but they don't always):* One parent contributes more genetic material; for instance, perhaps both parents contribute equally to the nucleus, but only one contributes any cytoplasmic nucleic acid.
  • One parent contributes the larger gamete and/or the "yolk" material.
  • One parent carries the conceptus in its body, or stays on the nest, or nurses the offspring, or in some other way pays a bigger biological investment.If those three things do in fact go together, that parent is the new individual's "mother" and the other parent is its "father".

    (There are good reasons to think they'll go together on other planets, too.)

    It is not always the case among Earth species that some individuals can be mothers but can't be fathers, and other individuals can be fathers but can't be mothers.

    An individual which, by mating, can become a mother of a new individual, but cannot become a father of a new individual, is called "female"; an individual which, by mating, can become a father of a new individual, but cannot become a mother of a new individual, is called "male"; an individual which, by mating, can become a mother of a new individual, and also, by mating, can become a father of a new individual, is called "hermaphroditic".

    In many Earth species all individuals are hermaphroditic. In some of these species any individual can fertilize any other individual; in others, even though all individuals are hermaphrodites, the species is divided into classes such that whether or not one individual can fertilize another depends on the classes to which each belongs.

    In many Earth species it is impossible for any individual to fertilize itself. On Earth, such species are often divided into "total outcrossing classes"; these are the largest groups within the species such that no two members of the same class can fertilize each other. There are often more than two such classes in an Earth species.

    In case there are exactly two total-outcrossing-classes, and one of them is "all females" and the other is "all males", then we can say this species has sexes. Not all sexually-reproducing Earth species have sexes in that sense.

    Among Earth species that have sexes, there are several biological strategies by which the sex of an individual becomes determined.* Genetic; the individual's sex is determined at conception.* XY sex chromosome system; a gene that determines maleness is on the Y chromosome; individuals who are XX are female.
  • ZW sex chromosome system. A gene that determines femaleness is on the W chromosome; individuals who are ZZ are male.
  • Diploid/monoploid system: diploid individuals are female, monoploid individuals are male.
  • Reverse diploid/haploid system: monoploid individuals are female, diploid individuals are male.
  • Autosomal genes determine the sex; the species doesn't have sex chromosomes, but there is more than one poly-allelic locus, usually on more than one pair of chromosomes, whose alleles, in various combinations, determine the individual's sex.
  • Incubation/gestation; before birth or hatching, the individual's sex becomes determined by the circumstances of its incubation or gestation (for instance, some crocodilians' sex is determined by the temperature at which they are incubated).
  • A combination of the autosomal chromosomes and the environment of incubation/gestation determines the sex.
  • Following birth or hatching, but before sexual maturity, adulthood, or puberty, the individual's sex is determined.

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    XENOBIOLOGY
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    Questions:
    1) How likely is it that any species's method of reproduction might require involvement of three or more parents?
    2) What if there were two fathers, each of whom contributed half of the nuclear DNA, and one mother, who contributed all of the cytoplasmic DNA, all of the nucleoli, all of the ribosomes, and all of the edit-RNA?
    3) Is a three-parent system more, or less, likely among species whose cells have three-stranded DNA instead of just two-stranded?
    4) Is a three-stranded DNA even possible at all? If so, is it even compatible with sexual reproduction at all?
    5) If there are three parents per individual, how many sexes will there be? * Is "just one sex" a possible answer?
  • Is "two sexes" a possible answer?
  • Is "exactly three sexes" the only possible answer?
  • Could "more than three sexes" be a possible answer?
    6) If there are three parents per individual in an intelligent species, how does this affect the society's naming patterns and systems, inheritance patterns and systems, etc.?
    7) If every child had three parents, would the three parents be expected to live together to rear the child?

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    Don't forget to read that thread on CONLANG-L. It's got more stuff that might be interesting.

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    1) It's less likely than two-parent sexula reproduction, and would require a reason for the added complexity to the system of finding not one but two mates of the right sex(es). Maybe a very quickly mutating parasite or other reason why that much genetic reshuffling would be required.

    2) If three-parent reproduction existed, I could see either of your systems working.

    3 and 4) I don't think DNA can be three stranded, though there are similar acids that could be. However, you aren't mixing two sides of a DNA strand when animals sexually reproduce, but instead are mixing sets of chromosomes. I would expect a species with this form of reproduction would have one of the following: Three copies of each chromosome (one from each parent) in the neucleus, with one parent contributing any other genetic material, cytoplasm, etc. OR Two of each coming from two of the parents and the rest from the third.

    5) Probably one, as that would make things simpler, though it's always possible that there could be two or three sexes. I don't think more than that would be likely.

    6) I guess they could take one name from each parent, or a personal name and a family name from one parent, probably their "mother".

    7) Possibly. There could be any combination of care-takers: The one who gives birth/lays eggs alone, one of the parents that didn't give birth/lay eggs. both parent that didn't, the one who did and at least one who didn't, or even none of them and the child is just raised by the community. Do what you want with it.

    Posted June 27th, 2007 by bloodb4roses
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    Thank you, BloodB4Roses.
    1) It's less likely than two-parent sexula reproduction, and would require a reason for the added complexity to the system of finding not one but two mates of the right sex(es). Maybe a very quickly mutating parasite or other reason why that much genetic reshuffling would be required.
    Presumably, escaping the parasites' evolved advantages is the selective pressure in favor of sexual reproduction IRL. I wonder what kind of selective pressure would encourage a three-parent system?

    2) If three-parent reproduction existed, I could see either of your systems working.
    Is anyone aware of any conworld that has actually tried that? Or is anyone working on one?

    3 and 4) I don't think DNA can be three stranded, though there are similar acids that could be.
    AIUI and IIRC, it can be; but it requires a different pH.

    However, you aren't mixing two sides of a DNA strand when animals sexually reproduce, but instead are mixing sets of chromosomes.
    Yes, that's true. People who play around with three-parent reproduction, and people who play around with 3-stranded genetic material, sometimes forget there's no connection. That's really why I asked questions 3 and 4; to make people think about that.

    But mightn't a 3-stranded genetic material be much less prone to mutation? When it's copied, one of the new strands has two older strands to be compared against. (OTOH maybe the other copy is even more prone to mutation.)

    I would expect a species with this form of reproduction would have one of the following: Three copies of each chromosome (one from each parent) in the neucleus, with one parent contributing any other genetic material, cytoplasm, etc. OR Two of each coming from two of the parents and the rest from the third.
    The latter system is the one I have the easiest time visualizing; two "fathers", each of whom contributes half of the nuclear genes, plus a "mother" who contributes everything else -- all of the cytoplasmic DNA, all of the edit-RNA, all of the ribosomes, all of the nucleoli.
    Does anyone know of a conworld in which either of those two kinds of three-parent reproduction is the norm for one of the important species? Or is anyone working on one? Who knows of, or is working on, one with all three parents contributing a third each of the nuclear genes? Who knows of, or is working on, one with two parents contributing half of the nuclear genes each, and the third parent contributing everything else?

    5) Probably one, as that would make things simpler, though it's always possible that there could be two or three sexes. I don't think more than that would be likely.
    Well, with just two parents, all kinds of things actually happen IRL *here* on Earth that just don't seem all that "likely".
    Why are there total outcrossing classes at all?
    Given that there are, why can one of them only become fathers and the other only become mothers?
    OTOH among species which are rare, and the chances of running into a conspecific are slight in the first place, it's advantageous to be hermaphroditic; your date for Saturday night can be the first other individual of your species you run into. Among flatworms, there is then a competition; both would prefer that the other one be the one who becomes pregnant; but both would prefer that the mating take place, more strongly than that the other be the impregnated one. Flatworms can be fertilized on any part of their body; each has two penes, which are sharp-pointed like hypodermic needles. The mating consists of a "dance" or "fencing" in which each attempts to penetrate the other without being penetrated itself.
    But if an animal species isn't rare, more often than not it's divided into male and female, and each animal, at any particular time, is just male or just female. Why is that?

    6) I guess they could take one name from each parent,
    Kind of what I was thinking of.
    or a personal name and a family name from one parent, probably their "mother".
    Seems likeliest. Is anyone working on such a species?

    7) Possibly. There could be any combination of care-takers: The one who gives birth/lays eggs alone, one of the parents that didn't give birth/lay eggs. both parent that didn't, the one who did and at least one who didn't, or even none of them and the child is just raised by the community. Do what you want with it.
    You are right, of course. Among *real world* species on Earth, often the father puts more time and effort into rearing the young, once they hatch or wean or get born or whatever, than the mother. (OTOH, often not.) Is anyone working on such a thing? Has anyone heard of such a thing in anyone else's work?

    Posted June 27th, 2007 by eldin raigmore
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    The only mention of a three-parent system I've seen is in the kid's books Animorphs. The main villain-race, the Yerks(sp) would combine three individual's genetic material to form many new individuals, but the parents were destroyed in the process.

    Posted June 28th, 2007 by bloodb4roses
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    Thanks! I've never looked at that series.
    Here's what I found via Google:
    http://en.wikipedia.org/wiki/Yeerks#Reproduction
    Reproduction
    Yeerks reproduce by fusion followed by fission. Three parent Yeerks merge into a single organism, which then breaks apart into hundreds of separate grubs, destroying the parents in the process. Yeerks do not have different sexes; presumably any three random Yeerks can fuse in reproduction. Nevertheless the Yeerks are usually referred to as "he" or "she" in the novels based on their host's sex (usually by a human or Andalite, who do have different sexes).


    "Their Majesties' Bucketeers" by L. Neil Smith contains another fictional species who have three-parent reproduction. They also have three sexes. But this particular novel doesn't explain anything at the subcellular level; in fact most of Smith's aliens aren't explained much more clearly than Piers Anthony's are.
    Their Majesties' Bucketeers is the third novel set in the Gallatin Universe. The story is a pastiche of the Sherlock Holmes tales by Arthur Conan Doyle, introducing the Lamviin, a trilaterally symmetrical race of aliens native to the arid planet of Sodde Lydfe. Their Majesties' Bucketeers introduces characters who would later interact with others in the Gallatin Universe.


    I believe Piers Anthony had a four-sex species with three-parent reproduction. The offspring was of whichever sex none of its parents belonged to. The last of the three parents to join the mating, determined which of the other two became pregnant. Again this was not explained at a cellular or molecular level (nor at any level in between cells and molecules); but Piers Anthony has living, intelligent magnets, and beings who have bells growing from them which are used in mating, and all sorts of other stuff that's very implausible; he doesn't try to be scientific.

    Posted June 28th, 2007 by eldin raigmore
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    In David Gerrold's "Chtorr" there is a species called "bunnymen and libbets". At least I think it's just one species. The bunnymen are the males and the libbets are the females.

    In that species the males have three parents; two fathers and a mother.
    The females have just two parents, a mother and one father.

    The only way I have thought of that this might work is that the males are triploid and the females are diploid.

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    The Chtorr ecology is heavy on parasites; or, rather, on symbiosis. There is a prevalent, versatile parasite, not quite an ectoparasite and barely an endoparasite, that can infest absolutely any animal that's large enough (bigger than a few inches) and has a long enough lifespan.
    Not only all the Chtorr animals, but any Earth animal that lives in the Chtorr-taken regions long enough, gets covered with a coat of synaesthetic "hair".
    Most of the bodies of these parasites are outside the bodies of their hosts; but they penetrate the skin with "roots" which then hook into the nervous system.
    They're actually symbiotic; they allow their hosts to have chemosenses -- taste and smell -- all over their bodies, as well as low-resolution hearing, and even lower-resolution "sight" (or, at least, sensitivity to light).

    Although by the time the Chtorr ecology invaded the Earth, these parasites had evolved enough restraint that they did not invade the respiratory nor alimentary nor genital nor urinary tracts even of Terrestrial hosts, which had evolved no resistance against them; it's easy to imagine that all living large Chtorran animals are descendants of ancestors which had had to survive infestations by much more virulent, ancient ancestors of these parasites.

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    The triploid organisms -- the bunnymen, the males -- have a 50% greater chance of being heterozygous for any particular trait than any diploid organism would have.
    As the "sickle cell" trait in RL humans shows, being heterozygous for certain traits can combat certain parasites.
    A heterozygous individuals red blood cells will not sickle unless infested with the malaria parasite; but if infested, will sickle, killing the parasite (and the red blood cell) before it can reproduce and kill the RBC and go on to infest other RBCs.
    An individual who is homozygously normal, does not have this protection against malaria.
    An individual who is homozygous for the sickle-cell trait, unfortunately, has RBCs that will sickle whenever they stay too long in a low-oxygen high-carbon-dioxide environment of the right pH; ordinarily these individuals die before having children (unless treated?).

    Anyway; suppose a given locus on the bunnymen's genes has three alleles; imagine they are equally common.
    One out of every nine bunnymen will be homozygous (one out of twenty-seven will be homozygous for each of the three alleles).
    Two out of every three bunnymen will be heterozygous, having two copies of one allele and one copy of another allele (six different combinations).
    Two out of every nine bunnymen will be three-way heterozygous, having all three alleles.
    But for the libbets, one out of every three will be homozygous, and two out of three will be heterozygous; none, of course, will be three-way heterozygous.

    However there will be greater diversity among the daughters of each given bunnyman/libbet couple than there would be if the bunnymen were diploid instead of triploid; there are 3*2=6 combinations each can inherit from her parents, instead of just 2*2=4. So a parasite which had evolved an efficient way to attack the preceding generation would have much less chance that the same method would work on the next generation; and this difference would be greater, even for the libbets, than it would be if the bunnymen were diploid instead of triploid.

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    How does that sound for a justification of three-parent reproduction?

    Posted June 29th, 2007 by eldin raigmore
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    I think so.

    Posted June 29th, 2007 by bloodb4roses
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    Flatworms can be fertilized on any part of their body; each has two penes, which are sharp-pointed like hypodermic needles. The mating consists of a "dance" or "fencing" in which each attempts to penetrate the other without being penetrated itself.
    But if an animal species isn't rare, more often than not it's divided into male and female, and each animal, at any particular time, is just male or just female. Why is that?

    Maybe the first half answers the second. If a mate is easy to find (e.g. in a herd), then giving an individual the chance to avoid becoming pregnant by mating will cause wasting of their effort. If there are traits that makes individuals either just male or just female, then those individuals will avoid a lot of the bother of both trying to be the father and not the mother. The females won't have to try and the males won't need to.

    Posted June 29th, 2007 by simon.clarkstone
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    Although by the time the Chtorr ecology invaded the Earth, these parasites had evolved enough restraint that they did not invade the respiratory nor alimentary nor genital nor urinary tracts even of Terrestrial hosts, which had evolved no resistance against them; it's easy to imagine that all living large Chtorran animals are descendants of ancestors which had had to survive infestations by much more virulent, ancient ancestors of these parasites.
    This sounds unrealistic. In the real world, a non-dangerous disease in one population will often turn out to be deadly in a population that has not encountered it before. The hosts' defenses and the parasites' attacking will have moved towards one another to reach an equilibrium, with both being quite powerful. The parasite would ravage the new host population, or would die because it needed part of the hosts' defences to live, or both at once.

    Evolution exploits anything exploitable you give it, including things that are supposed to hinder rather than help. And obscure bugs in your universe simulator, if simulated.

    Posted June 29th, 2007 by simon.clarkstone
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    This sounds unrealistic. In the real world, a non-dangerous disease in one population will often turn out to be deadly in a population that has not encountered it before. The hosts' defenses and the parasites' attacking will have moved towards one another to reach an equilibrium, with both being quite powerful. The parasite would ravage the new host population, or would die because it needed part of the hosts' defences to live, or both at once.
    Evolution exploits anything exploitable you give it, including things that are supposed to hinder rather than help. And obscure bugs in your universe simulator, if simulated.
    I don't know why, but Gerrold had it that these particular parasites didn't kill humans, at least not at all quickly. Furthermore the infestations didn't do a good job of sticking around in case the humans left the Chtorr-dominated zones.
    Since Gerrold's characters didn't understand the Chtorr ecology, perhaps he didn't think he ought to explain it to his readers yet. (Or just possibly he had no explanation; I don't know.)

    Posted June 29th, 2007 by eldin raigmore
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    Flatworms can be fertilized on any part of their body; each has two penes, which are sharp-pointed like hypodermic needles. The mating consists of a "dance" or "fencing" in which each attempts to penetrate the other without being penetrated itself.
    But if an animal species isn't rare, more often than not it's divided into male and female, and each animal, at any particular time, is just male or just female. Why is that?

    Maybe the first half answers the second. If a mate is easy to find (e.g. in a herd), then giving an individual the chance to avoid becoming pregnant by mating will cause wasting of their effort. If there are traits that makes individuals either just male or just female, then those individuals will avoid a lot of the bother of both trying to be the father and not the mother. The females won't have to try and the males won't need to.


    I don't know. I think that having one sex that is specialized in giving birth also frees up the other sex to specialize in activities where pregnancy would be a hindrance if not an impossible obstacle.

    Also, IIRC, there was (or is) a theory on sex differentiation that suggested that females would get slighter over time because they can pass through the birth canal more easily that way, while males will get bigger so they can be stronger. I'm not sure I really buy that, and it doesn't say much about egg-laying creatures. Thus, I made Xala females the stronger (and smarter) sex -- and also gave Kesatans very little sex differentiation at all (I'm still debating whether I'll allow them to spontaneously change sex).
    ________

    As for three-parent reproduction: I don't think it's very plausible. I once thought up a three-parent race (though I didn't work out reproductive details) that also had three sexes, but reflecting back on that, it probably wouldn't work to well.

    Posted July 2nd, 2007 by Fonori
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    Fonori
     
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