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Thread: Dumb Luck Reproduction

  1. #1 Dumb Luck Reproduction 
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    Flowering plants love to flirt. It seems unnatural, even lewd, that a plant would grow an enormous sexual structure loaded with male and female gametes dangling so close together, almost touching. Why not just do it?

    The plant is waiting for a chance agent to mix things up. Often a bee. Variation is that important. Apparently the plant can't trust itself to roll its own damn dice. Why is that? It seems a closed system can't cut it... why?

    Some plants let wind randomize fertilization. The great conifers come to mind. They needn't invest so much in building flowers or offering nectar. And perhaps it is because wind is not fickle enough that the conifers push luck another way: a single tree dumps loads of seed almost straight down, ensuring none if any of a year will reach maturity. Of course the tree could more efficiently drop a few fat seeds guaranteed to survive, but that wouldn't be very random would it?

    I'm still trying to get my mind around this.

    How about other kingdoms? Sometimes the coast waters turn pink or milky with spawn. I'd previously thought this was about maximizing offspring survival, but I guess I was wrong - it's about minimizing the surviving offspring, with a margin for survival. Eh?


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  3. #2  
    Forum Cosmic Wizard spuriousmonkey's Avatar
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    Nature doesn't care about waste as long as it is affordable.


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  4. #3  
    Forum Cosmic Wizard i_feel_tiredsleepy's Avatar
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    Also, flowering seems to work quite well. Those flowering plants are the most recently evolved group, and they make up the majority of the land plants extant today. All that grass may not look like a flowering plant, but it is, the flowers are just tiny.

    Few offspring tends to correlate with a large parental investment, either in the form of some sort of highly resistant seed, like the bulb of a tulip, or the kind we associate with mammals. The cost for an organism to have 1-3 offspring and making sure they survive to maturity over a long period of time, will not necessarily be better than producing 1000 babies with a 1% chance of survival.

    Edit: Also consider if you're a minnow, there's not much you can really do to prevent your offspring from being eaten anyway, so the best thing to do is probably to have as many babies as you can.
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  5. #4  
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    I'll rephrase the proposition. A strategy of having many offspring doomed to die by pure fluke is genetically advantageous in itself. Spawning vast numbers is not an attempt to maximize survival, rather it's to maximize fluke.

    Why don't men produce just one sure-fire sperm? Why do women cast their eggs down perilous ways to an uncertain lodging? It seems that much of reproduction, in many species, is built to fail most of the time.
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    Forum Cosmic Wizard i_feel_tiredsleepy's Avatar
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    Well if you think about how that would work is that you get a inverse correlation between parental investment and number of offspring. It would be incredibly expensive to make that one sure-fire sperm and make sure the offspring survives, and then you also would have to make sure that the female has one surefire egg. I don't see how this would be likely to come about by natural selection, it would be incredibly unlikely when it seems to me natural selection would usually favour the patterns of few offspring with high investment and many offspring with little investment.

    How would an organism insure that the sperm is always viable, a surefire method of DNA replication is as yet unknown, errors always happen.
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  7. #6  
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    Quote Originally Posted by i_feel_tiredsleepy
    How would an organism insure that the sperm is always viable, a surefire method of DNA replication is as yet unknown, errors always happen.
    It wouldn't and it doesn't now. If I'm not mistaken, first sperm to pop in gets accepted (and others blocked) - before fertilization is tried. If half the sperm contain dud genes the odds don't change because you try 1 of 100 or 1 of 280,000,000. However the odds of getting at least one human sperm to reach the egg - I guess you'd agree - should be magnitudes greater if the sperm were only doubled in size e.g. the size of mouse sperm. In that case an investment of just 1/2 or 1/20 sperm volume should still perform better.

    As it is, a female may be trying to conceive, and still no luck. Dumb luck. Her body's partially to blame. She's got to roll just one egg down the convoluted bowling lane of her fallopian tube, timed to hit a sperm in the middle run, then roll on clear of all walls and finally nest it just so in her uterine wall. It's like those amusement park games rigged so you end up playing twenty times to win the puffy bear. Why does the female make the fate of her own eggs so uncertain?

    Now that I think about it, copulation and ejaculation seem ...geared... to further randomize which sperm get ahead. Like a craps shoot, fluke is not just of the dice but also of the shaking up and casting forth. I trust animals breed that way for good reason.

    And what's with all the spilled sperm? When you sit down at a casino, does the dealer let you pick one deck of two to play with, discarding the other? Why?
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    Just as a note, most if not all Pinophyta (pines, cypresses, etc) don't drop their seeds straight down, most cones open while still in the foliage and the wing seeds (think maple seeds) are carried by the wind to other locations. The exceptions, eg, Taxaceae, Cephalotaxaceae, etc.. use fleshy covers on the seed to attract animals who eat the "berries" and move the seeds to other locations. So this example isn't actually viable in the discussion.
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  9. #8  
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    Quote Originally Posted by Pong
    Quote Originally Posted by i_feel_tiredsleepy
    How would an organism insure that the sperm is always viable, a surefire method of DNA replication is as yet unknown, errors always happen.
    It wouldn't and it doesn't now. If I'm not mistaken, first sperm to pop in gets accepted (and others blocked) - before fertilization is tried. If half the sperm contain dud genes the odds don't change because you try 1 of 100 or 1 of 280,000,000. However the odds of getting at least one human sperm to reach the egg - I guess you'd agree - should be magnitudes greater if the sperm were only doubled in size e.g. the size of mouse sperm. In that case an investment of just 1/2 or 1/20 sperm volume should still perform better.

    As it is, a female may be trying to conceive, and still no luck. Dumb luck. Her body's partially to blame. She's got to roll just one egg down the convoluted bowling lane of her fallopian tube, timed to hit a sperm in the middle run, then roll on clear of all walls and finally nest it just so in her uterine wall. It's like those amusement park games rigged so you end up playing twenty times to win the puffy bear. Why does the female make the fate of her own eggs so uncertain?

    Now that I think about it, copulation and ejaculation seem ...geared... to further randomize which sperm get ahead. Like a craps shoot, fluke is not just of the dice but also of the shaking up and casting forth. I trust animals breed that way for good reason.

    And what's with all the spilled sperm? When you sit down at a casino, does the dealer let you pick one deck of two to play with, discarding the other? Why?
    That's a really good question i've never thought about that before. Would be a great evolutionary advantage. The more randomization of a breeding process, the more variety, the greater chance of survival of the genes. Which in term would promote more randomized breeding. Nice... Thanks for bringing that to my attention.
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  10. #9  
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    A major reason why mammals produce millions of sperm is simply that they are not the only sperm trying to reach an egg. If a male copulates just after another male has also done so, the chances of his sperm being the winner in the race is much greater if there are lots of sperm. So evolution favours the producer of many sperm.

    Even among humans, supposedly monogamous (ha, ha), there are numerous occasions where a copulation follows a previous one by a different male, and sperm are in competition. It is by no coincidence that the human penis has the perfect design to shovel out another man's semen, when inserted.
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  11. #10  
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    Skeptic hit on an important point, sperm competition. Chimpanzees have the largest testes size to body size ratio across primates and it's because an estrous female will mate with every male in the group. Gorillas have some of the smallest, because they ensure by physical force that no other males are around to even attempt to mate with their females. Gorilla sperm is very low in number and a lot of them are mutated with two heads or the swim in circles etc. And it's fine because there's no competition with other males' sperm. They can leisurely make their way to the female's egg.

    Looking at the human female reproductive system, however, gives us an idea of why it may be advantageous to have a system that fails so often. 30 - 40% of all conceived fetuses are miscarried within the first week. 70% of all conceived fetuses are miscarried within the first trimester. If the fetus makes it past the first trimester, odds are very good that it will survive to birth. But why are so many lost prior to that point?

    Reproduction is very expensive, and it's especially expensive for humans. Towards the end of gestation and in particular while nursing, a lot of energy will be drawn out of the mother, and that energy will be used to make sure the baby accomplishes very important growth. How well babies grow in this period has long lasting effects on their life; birth weight correlates with many measures of disease and mortality.

    Total parental investment by humans in each single offspring amounts to 18+ years of support. Very few animals can match us in this investment. Now: do we want to waste 18 years of effort on an offspring who is more likely to die before reproducing themselves? Do we want to waste effort on raising an infant with a critically low birthweight that virtually guarantees they'll suffer as adults? No. That's not something natural selection would favor.

    There is a lot of evidence to suggest that many of the human fetuses that are lost so early in pregnancy are lost because either the fetus is inferior (genetic abnormalities, a failure to strongly implant a placenta that will be key to nutrient intake later in pregnancy) or because the mother is in a critical energetic state that makes it unlikely she'll be able to meet the infant's nutritional needs later in pregnancy and nursing.

    What appears to be a high rate of failure are the results of a system that is sensitive to key factors that effect the likelihood of success of an attempt at reproduction. The plus side of this system is that a fetus who makes it through all these barriers is likely to be very high quality, and as animals that only have a very few offspring, making sure each one is high enough quality to survive is important.
    Man can will nothing unless he has first understood that he must count on no one but himself; that he is alone, abandoned on earth in the midst of his infinite responsibilities, without help, with no other aim than the one he sets himself, with no other destiny than the one he forges for himself on this earth.
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  12. #11  
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    I do see truth in everybody's counterpoints. And I appreciate the consideration of my odd angle.

    Rewind to the questions that began this speculation:

    Why don't self-pollinating plants just clamp their male and female sex organs together? Instead they rely on fluke fertilization e.g. pollens tumbling randomly across a narrow gap. And all flowering plants go to great lengths (flowers!) to invite random outside forces into fertilization, like the play of breezes or the hit-and-miss of raindrops. Why?
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    Forum Cosmic Wizard paralith's Avatar
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    .... are you just talking about sexual reproduction in general? The general advantage is an increase in genetic diversity of the offspring, which makes it more likely that at least some of them will have the right genetic variations to handle unexpected environmental challenges. And since plants can't move themselves to find a partner to swap genes with, they have to find ways to send their gametes across the spaces. Some plants, however, have the ability to self fertilize in addition to cross fertilization, so that if there is no gene swapping partner within a reasonable distance they can still have offspring. I thought you were asking something different, sorry.
    Man can will nothing unless he has first understood that he must count on no one but himself; that he is alone, abandoned on earth in the midst of his infinite responsibilities, without help, with no other aim than the one he sets himself, with no other destiny than the one he forges for himself on this earth.
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  14. #13  
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    Quote Originally Posted by paralith
    The general advantage is an increase in genetic diversity of the offspring
    Alright. Now let's consider reproduction as closed vs. open system. Open would be casting gametes to the external lottery of wind, so the parents have absolutely no influence over which get fertilized and with whom. Closed would be under sexual selection... extremely closed example being artificial insemination and then culling those with unwanted genes. Which allows greater diversity?
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  15. #14  
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    Well, obviously if you're consistently selecting for a certain set of traits or genes over time, at least at those loci the population will become less diverse/variable.

    Of course, when understanding why a species has evolved one particular reproductive strategy requires looking at more factors than just genetic diversity. Plants have very little control over whose pollen ends up in their flowers, so they could very well end up with a deletrious combination. Sending out lots and lots of pollen, then, is also a way to ensure that at least some of your pollen will find a partner with whom it can make a beneficial combination. Genetic diversity of offspring is probably also more important for plants, since seeds that fall in a disadvantageous spot can't get up and go somewhere else. But, maybe if some of them have the right combination of genes, they'll still do ok.

    (Plants don't completely lack control, though. They may not know whose pollen will end up in their flowers, but the pollen still has to travel through the flower to get to the area where the eggs are, which allows the plants some time to potentially screen what pollen makes it there.)

    For animals like humans, we can behaviorally counteract a lot of things that plants can only hope to handle with the genes they inherited. And since we put so much effort into each individual offspring, we want to do as much as we can to find an advantageous partner, both in genes and in ability/willingness to help invest. (Though of course, we may choose to find those two contributions in two different people.)
    Man can will nothing unless he has first understood that he must count on no one but himself; that he is alone, abandoned on earth in the midst of his infinite responsibilities, without help, with no other aim than the one he sets himself, with no other destiny than the one he forges for himself on this earth.
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  16. #15  
    Forum Cosmic Wizard i_feel_tiredsleepy's Avatar
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    Quote Originally Posted by Pong
    I do see truth in everybody's counterpoints. And I appreciate the consideration of my odd angle.

    Rewind to the questions that began this speculation:

    Why don't self-pollinating plants just clamp their male and female sex organs together? Instead they rely on fluke fertilization e.g. pollens tumbling randomly across a narrow gap. And all flowering plants go to great lengths (flowers!) to invite random outside forces into fertilization, like the play of breezes or the hit-and-miss of raindrops. Why?
    Well considering plants can't move. Plant lifecycles go through a haploid and diploid stages. For mosses they live out most of their life as a haploid organism, some will produce male gametophytes, some female, some both. They rely on rainfall to allow their sperm to swim over to the ova on another moss. The ova is fertilized, turned into a diploid spore, dispersed by the wind, then there's meiosis and a haploid lifestyle starts again. Ferns reproduce by producing haploid spores that are dispersed by the wind, once these spores land they develop into a structure called a prothallus that produces male and female gametes, then rain happens and the sperm either fertilize themselves or preferably a neighbouring prothallus. Then a bunch of ferns grow.

    Those are the plant reproductive systems that existed prior to flowers and wind dispersal of male gametes to stationary female gametes. That in combination with what Paralith said, shows that flowering plants have developed a reproductive system much more advantageous than what came before. It's actually quite impressive.

    Plants can prevent deleterious breeding through rejection of spores or by producing only male or only female plants to prevent inbreeding. I remember very vaguely from the one plant biology course I took, that their are a number of markers and points in development where the flower is capable of aborting the embryo.
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  17. #16  
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    Okay, you've both confirmed that selection may be more or less random. It may include naturally chaotic selection as in rain scattering, and ...artificial... selection as in sexual selection and parental abortion/intervention.

    I'm sure "artificial" selection isn't the right term here. What I'm pointing to is selective forces from within the species (parental gene expression) itself. I think of that as closed system vs. open system.

    Intuitively, I'd think that closing up and self-managing fertilization - unto the species I mean not self-fertilization - would be advantageous. The species can maximize survival of its gametes with the minimum investment... then try the various offspring in the open system of natural selection. Humans basically employ this strategy - we don't let bees decide which sperm go where. But then we throw it all to chaos by growing a virtual naturally selective environment within our reproductive organs, and at considerable expense too.

    Paralith reminded that an inbuilt high failure rate helps to addle out the unfit. Makes sense. The sheer number of failures is amazing. And as a rule the process discriminates kinda wildly, so that at any one stage the basically viable have "a fair chance". Maybe a statistician grasps it better. It's like a machine that accepts quarters for the 25 candy, but instead of testing individual coins for counterfeit it demands about seventy million dollars in change, then tumbles all that through centrifuges, discarding all but one, because the survivor of this mad process "is probably a quarter".

    ***

    The story of Wilbur the pig in Charlotte's Web cutely illustrates the play of open vs. closed selection, and fluke vs. meaningful selection. Wilbur enters life as the runt of a litter, probably because of birth order (First born use the teats nearer a sow's head, which produce more milk). By dumb luck he's seventh of a litter with only six working teats available. There we have fluke strongly favoring one piglet over another, regardless of genetic makeup, and (contrary to lay reason) this fluke is engineered within the "closed system" of the species itself. The farmer's daughter feels sorry for the runt and removes it from cruel "natural" selection by fostering it. Throughout the plot farmer Zuckerman's axe looms large however. The pig turns out to have a boisterous and friendly disposition, so with a combination of environmental fluke and surprisingly adaptive genes (it's a radiant pig) fairs pretty well.
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  18. #17  
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    Pong, I'm not entirely sure I'm following your idea, so let me first repeat it back to you in my own words - that way, you can tell me if I'm just totally up the creek. :P (Sadly, your cute example didn't make it completely clear for me.)

    A completely "open" sexual reproduction system is one where the the parents simply find someone, apparently they don't care who, to mix genes with, have the offspring, and then the offspring are on their own to try and survive as well as they can in the environment. A "closed" sexual reproduction system is one where the parents put a lot of time and effort into finding the right mate to combine their genes with. Once the offspring are born they're just on their own again, but this time they have this really good combination of genes to start out with, thanks to the efforts of their parents.

    If what I said above is not true to your idea, then you can ignore what I've written below if you want.

    I always return to a cost-benefit analysis when talking about selection, because it really helps me to understand why certain traits or groups of traits have been selectively favored over others.

    Number one: what are the costs to the parents of spending a lot of time finding the right mate? It depends on how difficult mates are to find. It depends on if there are any reliable ways that one individual can assess the suitability of the other individual's genes relative to their own. It depends on how many options there are in the first place. These all factor into the costs, and these costs could be quite high.

    Number two: what are the benefits? If the environment is stable, such that the environment you know now will probably be the same for your offspring, and you know what gene combinations are most likely to help your offspring survive in that environment, then it might be really beneficial to make sure you have those gene combinations. But what if you don't know what the environment is going to be like? What if you don't know what genes you really should be aiming for? Especially if the costs of putting a lot of effort into finding a specific type of mate are really high, it simply may not be worth pursing a "closed" reproductive strategy.

    You also seem to be forgetting that not all animals just leave their offspring on their own to deal with the environment all by themselves after birth. Sure, you can do the best you can within reasonable costs to find a good genetic match up. But if you decide to invest time and effort in the offspring after birth as well, you can alter some of those environmental conditions so that your offspring's development, given the genes that it has, is the best it can be. If you are in a position to do this, then putting more effort into the pre-birth mate selection may not be worth it.
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  19. #18  
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    Quote Originally Posted by paralith
    A completely "open" sexual reproduction system is one where the the parents simply find someone, apparently they don't care who, to mix genes with, have the offspring, and then the offspring are on their own to try and survive as well as they can in the environment. A "closed" sexual reproduction system is one where the parents put a lot of time and effort into finding the right mate to combine their genes with. Once the offspring are born they're just on their own again, but this time they have this really good combination of genes to start out with, thanks to the efforts of their parents.
    I'm thinking more about the act of reproduction, than parenting strategies. But yeah that's kinda it.

    I mean open and closed in the neutral sense of open and closed systems. For example a greenhouse is a closed system, while pollination by wild insects is a relatively open system. All living things are "closed" in some ways, "open" in others. They self-regulate and reproduce, yet they also respond and adapt.

    I'm saying that many species could regulate their reproductive function as neatly closed energy efficient systems that leave nothing to chance, but for good reason they don't. And strangely they spend a large amount of energy inviting or engineering external or uncontrollable factors to basically mess with their own reproduction.

    I think they're conforming with a "law" which states no closed system can survive indefinitely. In practice the closing of an information system leads to usually rapid demise, for example by looping. These concepts aren't normally generalized to reproductive systems but I'm giving them a try. I'm suggesting that incorporating fluke factors - which have no relation to real-world fitness - may be a good compromise between that law and reproduction. See, you avoid the perils of the closed system, and do it without getting bound (closed) to the fate of another species, like the bee, or any other feature of the environment. A dice roll is most reliable to this end, just because the result depends on nothing.


    Quote Originally Posted by paralith
    You also seem to be forgetting that not all animals just leave their offspring on their own to deal with the environment all by themselves after birth. Sure, you can do the best you can within reasonable costs to find a good genetic match up. But if you decide to invest time and effort in the offspring after birth as well, you can alter some of those environmental conditions...
    No I'm not forgetting. I'm looking at how species balance the opposing needs of reproduction and diversity.

    If I fix the environment to suit my offspring, that's a plus for reproduction and a minus for diversity. It's "closing" part of the open environment into my own system, where I can regulate it. That environment then is really part of the species, just like a dirt playground is part of humanity and a rose blossom is part of honeybees. Playgrounds and roses can't be allowed to diverge much, and we wont' diverge from them either. Who knows after long symbiotism the relationships might loose original meaning and grow weird. Life is always trying to close things up, and it's basically our "way" but it's a dangerous way. Imagine if we settled into a niche and stopped evolving.

    ***

    Quote Originally Posted by paralith
    costs of putting a lot of effort into finding a specific type of mate are really high
    Did you re-read my Dumb Daughter hypothesis? Remember I proposed that male plumage could pay the costs of female time and attention selecting an appropriate mate.. so she can devote all energy to basic survival and laying eggs.
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  20. #19  
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    Mate selection is pretty much universal among all those organisms with sufficient brain power. There are fish that simply squirt their seed into the ocean, but higher animals tend to be somewhat choosey about who they mate with. At least, the females are, and that is probably because they have limited reproductive resources and cannot waste them on a mate that donates inferior genes. Males can often spray their seed around, and simply make more.

    The point is that, for mate selection to be so nearly universal among animals with brains, it must carry great benefits. Even quite simple fish, like the stickleback, have been shown to be selective in reproductive partner.

    It makes sense. For a female, the investment in finding a mate with good genes is minimal compared to the investment of biological resources for reproduction overall.
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  21. #20  
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    flesh is cheap


    why spend time building things with the best chance for survival if there's still a chance it will fail



    10 seeds with 80% chance of sucess means 8 seeds will grow

    100 seeds with 40% chance of sucess means 40 seeds will grow
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