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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.
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]
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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. |
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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. |
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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). |
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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. |
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<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... |
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didn't I just read the other day that Europeans are actually Neanderthal crossbreeds ? |
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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. |
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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. |
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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? |
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[FT], That would explain my hairy legs, music tastes, and occasional urge to bang on rocks. |
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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! |
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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. |
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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). |
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\\But I don't think I talked about carriers.\\ |
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\\Local circumstances and a founder effect have led to a
selective advantage for carriers of Downs syndrome in this
colony\\ |
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But, in any case, the cancer link is interesting. |
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//hairy legs// actually I was thinking of pointy caucasian noses. |
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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. |
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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. |
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oh. I read "download world". |
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I thought this was going to be a theme park. |
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//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.// |
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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. |
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//one can have a nonadvantageous (or even
disadvantageous) phenotype come to dominate
via founder effect// |
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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). |
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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. |
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[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. |
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//Interbreeding with Neanderthals doubted.// |
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May I refer to the comment of my esteemed and
prescient
colleague, [MaxwellBuchanan], above? I think I may. |
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// in one of the sequels // |
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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. |
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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. |
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