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Natural Science Forum / Biology / Evolution / July 2009Why Sexual reproduction is more popular
Hello, I want to ask why complex animals are usual divided into sexes and are not intersexual. I know some evolutionary explanation for advantages of sexual reproduction against asexual, but I've never heard explanation why sexual reproduction is not made by pairs of intersexual individuals. I now it is popular among invertebrates why it disappeard for vertebrates? I will be appreciate for any help like link to a book where is an explanation or even name of author ;). Best Regards Adam > I want to ask why complex animals are usual divided into sexes and are > not intersexual. I know some evolutionary explanation for advantages [quoted text clipped - 5 lines] > I will be appreciate for any help like link to a book where is an > explanation or even name of author ;). I have a page on that topic: http://alife.co.uk/essays/gender_division/ -- __________ |im |yler http://timtyler.org/ tim@tt1lock.org Remove lock to reply. >> I want to ask why complex animals are usual divided into sexes and are >> not intersexual. I know some evolutionary explanation for advantages [quoted text clipped - 9 lines] > > http://alife.co.uk/essays/gender_division/ Nice essay, Tim. But there are two features of animal hermaphroditism that you ought to mention and include in the essay. 1. Some hermaphroditic animals require reciprocal coitus. But plants don't/can't use this strategy. Instead, they broadcast the male pollen. Why don't plants engage in coitus? My guess is because they don't have a fixed shape. (Well, also because they are immobile). 2. Other hermaphroditic animals are serial hermaphrodites. But I don't think that any (presumably perennial) plants are. Note that a serial hermaphrodite is automatically sexually dimorphic and subject to both male-combat and female-choice forms of sexual selection. My own speculation is that serial hermaphroditism is the evolutionary precursor of dioecious sexuality. Perplexed in Peoria wrote: > "Tim Tyler" <seemysig@googlemail.com> wrote: >> http://alife.co.uk/essays/gender_division/ > > Nice essay, Tim. Thanks. It needs rewriting - but it makes a basic point and has some references. > But there are two features of animal hermaphroditism > that you ought to mention and include in the essay. > 1. Some hermaphroditic animals require reciprocal coitus. But plants > don't/can't use this strategy. Instead, they broadcast the male pollen. > Why don't plants engage in coitus? My guess is because they don't > have a fixed shape. (Well, also because they are immobile). This is true. However, how this relates to separated genders is not immediately obvious to me. It could be implicated - but you haven't proposed how. > 2. Other hermaphroditic animals are serial hermaphrodites. But I don't > think that any (presumably perennial) plants are. Note that a serial > hermaphrodite is automatically sexually dimorphic and subject to > both male-combat and female-choice forms of sexual selection. My > own speculation is that serial hermaphroditism is the evolutionary > precursor of dioecious sexuality. That is interesting and relevant. It weakens the argument for the "different roles" theory a bit. However, it doesn't weaken it terribly much. Control over development from birth provides more in the way of options for specialisation than is present with sequential hermaphrodism - which I understand is called "dichogamy". See: http://en.wikipedia.org/wiki/Dichogamy ....for the story with plants. -- __________ |im |yler http://timtyler.org/ tim@tt1lock.org Remove lock to reply. > Perplexed in Peoria wrote: >> "Tim Tyler" <seemysig@googlemail.com> wrote: [quoted text clipped - 16 lines] > immediately obvious to me. It could be implicated - but you haven't > proposed how. In the absense of reciprocal coitus protocols, non-sequential hermaphroditism is unstable because desirable mates in terms of female choice may not match the desirable mates for male-choice. You, yourself, may find that you are scored as a desirable male partner, but an undesirable female one. Hence you may have the incentive to focus your resources on one role over the other. But with reciprocal coitus protocols in place, if cheating can be prevented, there is no instability. A standard argument shows that resources should be equally divided between the sex roles. >> 2. Other hermaphroditic animals are serial hermaphrodites. But I don't >> think that any (presumably perennial) plants are. Note that a serial [quoted text clipped - 12 lines] > > ....for the story with plants. Thx for the link. My ignorance of botany is again revealed. I had been thinking in terms of plants expressing female one year and male the next. I hadn't even considered that the two sexes might be expressed sequentially in the same flower. Thank you Tim for answer, I founded Matt Ridley book mentioned in the essay and started to read it :). Thank you once more. On Jul 5, 1:36=A0am, "Perplexed in Peoria" <jimmene...@sbcglobal.net> wrote: > "Tim Tyler" <seemy...@googlemail.com> wrote: > > On Jul 2, 12:05=3DA0am, Adam Skrodzki <adamskrod...@gmail.com> wrote: [quoted text clipped - 16 lines] > that you ought to mention and include in the essay. > 1. =A0Some hermaphroditic animals require reciprocal coitus. =A0But plant= s > don't/can't use this strategy. =A0Instead, they broadcast the male pollen= .. > Why don't plants engage in coitus? =A0My guess is because they don't > have a fixed shape. =A0(Well, also because they are immobile). > 2. =A0Other hermaphroditic animals are serial hermaphrodites. =A0But I do= n't > think that any (presumably perennial) plants are. =A0Note that a serial > hermaphrodite is automatically sexually dimorphic and subject to > both male-combat and female-choice forms of sexual selection. =A0My > own speculation is that serial hermaphroditism is the evolutionary > precursor of dioecious sexuality. thank On Jul 7, 7:08=A0pm, "Perplexed in Peoria" <jimmene...@sbcglobal.net> wrote: > "Tim Tyler" <seemy...@googlemail.com> wrote in messagenews:h2r72u$5lr$1@d= arwin.ediacara.org... > > Perplexed in Peoria wrote: > >> "Tim Tyler" <seemy...@googlemail.com> wrote: > >> But there are two features of animal hermaphroditism > >> that you ought to mention and include in the essay. > >> 1. =A0Some hermaphroditic animals require reciprocal coitus. =A0But pl= ants > >> don't/can't use this strategy. =A0Instead, they broadcast the male pol= len. > >> Why don't plants engage in coitus? =A0My guess is because they don't > >> have a fixed shape. =A0(Well, also because they are immobile). [quoted text clipped - 4 lines] > > In the absense of reciprocal coitus protocols, non-sequential hermaphrodi= tism > is unstable because desirable mates in terms of female choice may not > match the desirable mates for male-choice. =A0You, yourself, may find tha= t > you are scored as a desirable male partner, but an undesirable female one= .. > Hence you may have the incentive to focus your resources on one role > over the other. > > But with reciprocal coitus protocols in place, if cheating can be prevent= ed, > there is no instability. =A0A standard argument shows that resources shou= ld > be equally divided between the sex roles. I had to look up what "reciprocal coitus" meant: in unilateral mating, only one critter inseminates the other, while in reciprocal mating, both critters inseminate each other. I am still not sure I understand the argument. However, the conclusion seems to involve some animals getting to use reciprocal coitus sometimes - and those animals being less likely to have divided genders. It seems fair enough - but I don't know enough about it to say very much. I don't know how common reciprocal coitus is. Also, I think we are supposed to assume that females can usually decide when they get fertilised - since they are in charge of their own plumbing. Just because some sperm is delivered, that doesn't mean the females have to use it. For example, they could do something like what ducks do - turn their reproductive tract into a maze of twisty passages for losing bad sperm in. "Duck genitals locked in arms race" - http://www.cosmosmagazine.com/node/1277 -- __________ |im |yler http://timtyler.org/ tim@tt1lock.org Remove lock to reply. |
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