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Downs World

What if?
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I was pondering the Neandertals. They were not that different from us (linked). If they interbred with modern humans that implies that they were the same species as us. Humans too. Much of their differences probably had to do with gene dose and regulation rather than difference is sequence. How did their society differ because of this? Was it chance and numbers that led to disappearance of Neandertals? Or did they have a selective disadvantage?

People with trisomy 8 differ genetically only in having extra copies of certain genes. Downs World is a scifi concept for a book or movie, along the lines of Brave New World or the linked Twilight Zone episode. A human colony (extraterrestrial, or earthly) is rediscovered after a dark age. Local circumstances and a founder effect have led to a selective advantage for carriers of Downs syndrome in this colony, with the result that the populace is comprised entirely (or almost entirely) of people with trisomy 8.

The book would ideally be written by a person or persons with a thorough knowledge of Downs syndrome: less the purely medical aspects and more the subtle cognitive differences that characterize high functioning people with Downs. As with other high SF, the description of a different human society would allow a new viewpoint on our own and what it means to be human.

bungston, May 28 2010

Neanderthals: not that different. http://www.nytimes..../07neanderthal.html
[bungston, May 28 2010]

Twilight Zone: Eye of the beholder. http://spacedoutinc...1/TwilightZone.html
Classic SF. [bungston, May 28 2010]

Brave New World http://en.wikipedia...iki/Brave_New_World
Even classicer SF. Or is that classicker? [bungston, May 28 2010]

Possible genetic advantage conferred by trisomy 21: cancer resistance. http://news.bbc.co..../health/8055342.stm
[bungston, May 28 2010]

Interbreeding with Neanderthals doubted. http://www.bbc.co.u...nvironment-19250778
[DrBob, Aug 17 2012]

[link]






       This book would ideally be written by a person or persons who know that Downs is caused by trisomy 21, not trisomy 8, and that you can't be a "carrier" for Down's.   

       In most cases, Down's is pretty devastating. The problem is that, because it's a trisomy, a very large number of genes are affected (ie, present in an extra copy), so that any advantages will generally be outweighed by disadvantages of disrupting such a large chunk of the genome.   

       There are cases of partial trisomy 21, which have a smaller adverse effect, but I'm not aware of any advantages (though there may be some).   

       The mildest Down's cases are really just examples of a much more widespread phenomenon of copy-number variation (extra copies of some genes), which is extremely common and responsible for much of human variation.
MaxwellBuchanan, May 28 2010
  

       <pit nicking>modern humans and neanderthals are more like lions and tigers than of the same species; as in, their offspring would be analogous to ligers and tiglons</pn>. Oh biology, what a wishy washy field are thee...
swimswim, May 28 2010
  

       art thou.
MaxwellBuchanan, May 28 2010
  

       I sure art.
swimswim, May 28 2010
  

       didn't I just read the other day that Europeans are actually Neanderthal crossbreeds ?
FlyingToaster, May 28 2010
  

       Yes, see [bungston]'s first link. However, given the past history of work on the Neanderthal genome, I'd keep an open mind for a few more months.
MaxwellBuchanan, May 28 2010
  

       Yeh, that trisomy thing is embarrasing. I am tempted to edit it correct but will leave it as a testament to ignance and lack of background reading. But I don't think I talked about carriers.   

       That said, Max: currently Downs phenotype is a grab bag exactly as you say. But not always devastating, also as you say and it would be these folks the story would be about. Re advantage: one can have a nonadvantageous (or even disadvantageous) phenotype come to dominate via founder effect, and selective advantage of a phenotype depends on many things, which can be artifically introduced because this is scif-fi. This actually would be an interesting aspect to explore in the story: what is genetic fitness?
bungston, May 28 2010
  

       [FT], That would explain my hairy legs, music tastes, and occasional urge to bang on rocks.
RayfordSteele, May 28 2010
  

       Trisomy 21 might protect from cancer (link). One could riff on this for the selective advantage for Downs in the colony: perhaps an environment which produces a high cancer risk? Maybe from something that happened to throw humanity into the dark age? Now this is sounding like scifi!
bungston, May 28 2010
  

       Larry Niven's "Known Space" series includes "Protectors" - humans that evolve into uber-beings after eating a plant that alters their DNA. Part of the premis is that there's are least one planet where every family of primative humans is guarded by a Protector. His Ringworld also hosts a variety of human species who have evolved into niches due to the size of their environment and general absence of other animals.   

       Niven also has a short story (in Man-Kzin Wars II) where the main character stumbles on a series of reserves, one of which hosts Neanderthals in stasis. He releases some. Hilarity ensues (not really).
phoenix, May 28 2010
  

       \\But I don't think I talked about carriers.\\   

       \\Local circumstances and a founder effect have led to a selective advantage for carriers of Downs syndrome in this colony\\   

       But, in any case, the cancer link is interesting.
MaxwellBuchanan, May 28 2010
  

       //hairy legs// actually I was thinking of pointy caucasian noses.
FlyingToaster, May 28 2010
  

       There was a sci-fi show awhile back (don't know the name, sorry), about a ship colony of dna rejects who have this or that birth defect, run by a doomed captain and kept in space so as to keep the planet free of their genetic mutations.   

       Earth becomes plagued by some random virus which makes people's cells start falling apart, however the isolated ship of dna rejects seems immune. Hilarity ensues.
RayfordSteele, May 31 2010
  

       oh. I read "download world".
pashute, Aug 17 2012
  

       I thought this was going to be a theme park.
hippo, Aug 17 2012
  

       //There was a sci-fi show awhile back (don't know the name, sorry), about a ship colony of dna rejects who have this or that birth defect, run by a doomed captain and kept in space so as to keep the planet free of their genetic mutations.//   

       That would be "The Hitch-Hiker's Guide to the Galaxy", coincidentally by DNA. Probably it's in the radio version somewhere, in the print version it's in one of the sequels.
Loris, Aug 17 2012
  

       //one can have a nonadvantageous (or even disadvantageous) phenotype come to dominate via founder effect//   

       But not in the case of Down's. Unless there were a huge advantage, it would vanish very fast. Not only are people with Down's syndrome much less fertile, but a proportion of their children will not have Down's (the egg or sperm has an equal chance of having two copies of Chr21, or the normal one copy).   

       I presume that trisomy 21 doesn't greatly increase foetal mortality; I also guess that tetrasomy 21 is lethal early in development. In this case, if both parents have Down's then, out of four fertilisations, one will be normal (disomic for 21), one will be tetrasomic and hence won't develop, and two will have Down's (trisomy 21). Hence, one in three live births would be normal.   

       [EDIT: it appears that tetrasomy 21 is not always fatal. However, it seems likely that live births with tetrasomy 21 are mosaic, with a good proportion of the cells having lost at least one of the extra copies; or perhaps an early division error has created some tetrasomic cells from an initial trisomy. Equally, you can have mosaic trisomy where some of the cells are trisomic and others are normal (disomic), with the severity of symptoms depending on the proportion and types of cells affected. Either way, though, normal individuals will crop up very frequently, and it's hard to imagine them not having a great advantage.
MaxwellBuchanan, Aug 17 2012
  

       //Interbreeding with Neanderthals doubted.//   

       May I refer to the comment of my esteemed and prescient colleague, [MaxwellBuchanan], above? I think I may.
MaxwellBuchanan, Aug 17 2012
  

       // in one of the sequels //   

       In the radio version, it's the second series - the Space Ark built by the Golgafrinchans to rid themselves of an entire useless third of their population.   

       As to the books, which of the "increasingly inaccurately named five-volume trilogy" contains the reference is pretty much certain to be The Restaurant At The End Of The Universe.
8th of 7, Aug 17 2012
  
      
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