Minimum population question

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McHell
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Re: Minimum population question

Postby McHell » Fri Oct 12, 2007 8:34 am UTC

... and then the colony ship of 300 meets 500 genetically inferior but aggressive locals, gets killed to the last man, and thinks: why didn't we go for 1000 instead? ... :shock:

Zake
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Re:

Postby Zake » Sat Oct 13, 2007 12:58 am UTC

evilbeanfiend wrote:surely you have to account for the rate of mutation somehow. perhaps BSG needs fewer as increased ration exposure from space travel is increasing genetic diversity


Ah, but remember we're not trying for diversity in general, but diversity of good genotypes. The mutations caused by interstellar radiation would almost entirely be deleterious ones, including the ones which cause problems when one has two copies of them. So it would actually make the problem worse.

McHell wrote:why didn't we go for 1000 instead? ... :shock:


Because only having three hundred people left more energy for the phaser arrays, rather than using it up on life support. :D

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McHell
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Re: Re:

Postby McHell » Sat Oct 13, 2007 1:06 am UTC

Zake wrote: The mutations caused by interstellar radiation would almost entirely be deleterious ones, including the ones which cause problems when one has two copies of them.

Indeed the key is that there's many more ways to break something than to improve it. [Something here being a gene or a complex interaction influenced by it.]

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mehmattski
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A slightly different approach

Postby mehmattski » Sat Oct 13, 2007 7:01 pm UTC

I was thinking about this more, and another issue with colonizing another planet will be preventing reproductive isolation between the Earth population and the colony population. Given enough time, of course, even very large populations are expected to generate mutations which prevent reproduction after secondary contact. But I think this problem can be reduced, so long as the colony is not forgotten and new colonists keep arriving from Earth.

If the ships aren't able to achieve near-light speeds and therefore might take many tens of generations to reach the new planet, then perhaps it would be best to send two ships, each carrying 300 (or 1000) colonists. Every generation, there could be an exchange of a few individuals- this would keep the gene pool of the entire colony population homogenized, and prevent fixation of mutations which would cause reproductive isolation.

Once the colonists reach the new planet however, reproductive isolation may not be avoidable, if the new planet requires selection to a new environment, and the byproduct of those genes selected prevent mating with Earth humans.

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McHell
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Re: Minimum population question

Postby McHell » Sat Oct 13, 2007 7:40 pm UTC

I don't think interbreeding among 2 isolated small populations will keep it closer to the reference population on earth --- yes because 2x 300 is better/more stable (because you're referring to genetic drift, I presume) than 1x 300 but that's it.
[There may be a non-drift component: adapting to life in a space station ---> you cannot avoid that.]

That said, it takes a lot to get reproductively incompatible; look at humans and all the shapes and sizes they have but still can happily interbreed. Even those from very inbred communities. And look at lions and tigers, even they succeed in getting some fertile offspring (one way better than other way). Nearly all circus lions and tigers appear to have some mixed blood for example. [But ligers are pretty unhealthy overall.]

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Re: Minimum population question

Postby blob » Sat Oct 13, 2007 7:54 pm UTC

Sending humans back and forth between planets may be difficult. But by the time we're colonising other planets, aren't we likely to have better genetic engineering technology? Instead of sending DNA inside people to be used in old fashioned reproduction, we could send it as information to be reconstituted the other side and used in 'population compatibility maintenance' gene therapy :mrgreen:

(edit)...actually, that would pretty much solve the inbreeding thing too, wouldn't it?
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Crazy Eddie
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Re: Minimum population question

Postby Crazy Eddie » Sun Oct 14, 2007 3:40 am UTC

I read in a book called 1491 that the American Indians had built up a population far larger than anyone had suspected until recently, and that 90+ percent of them fell to European diseases without ever laying eyes on a white person. Supposedly the initial migration to the Americas was so small, and so genetically homogeneous, that even after 10,000+ years the Indians had practically no resistance to European diseases, and the societies that the Europeans encountered in the centuries after contact can best be described as "post-apocylyptic"

Is that theory still generally assumed to hold water?

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Re:

Postby CatV » Tue Mar 21, 2017 8:37 am UTC

gmalivuk wrote:
Token wrote:
Pesto wrote:Are we assuming all the other things that go along with a destroyed Earth, like loss of technology and such?

Well, it's no fun if you can just clone your way back to genetic diversity.


Um... how would cloning create diversity?


Cloning would actually cause the opposite of genetic diversity unless it were combined with genetic manipulation, or cloning of individuals unable to reproduce.

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Re: Minimum population question

Postby eSOANEM » Tue Mar 21, 2017 10:57 am UTC

Crazy Eddie wrote:I read in a book called 1491 that the American Indians had built up a population far larger than anyone had suspected until recently, and that 90+ percent of them fell to European diseases without ever laying eyes on a white person. Supposedly the initial migration to the Americas was so small, and so genetically homogeneous, that even after 10,000+ years the Indians had practically no resistance to European diseases, and the societies that the Europeans encountered in the centuries after contact can best be described as "post-apocylyptic"

Is that theory still generally assumed to hold water?


I've certainly heard arguments like that a lot. I think usually it's argued that the relative lack of domesticated animals was to blame for the weaker immune systems rather than a lack of genetic diversity.

CatV wrote:
gmalivuk wrote:
Token wrote:
Pesto wrote:Are we assuming all the other things that go along with a destroyed Earth, like loss of technology and such?

Well, it's no fun if you can just clone your way back to genetic diversity.


Um... how would cloning create diversity?


Cloning would actually cause the opposite of genetic diversity unless it were combined with genetic manipulation, or cloning of individuals unable to reproduce.


They might have meant that you could clone dead folks to get genetic diversity back

Edit: shit, I hadn't realised this was a necro.
Last edited by eSOANEM on Tue Mar 21, 2017 11:44 pm UTC, edited 1 time in total.
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Re: Minimum population question

Postby Copper Bezel » Tue Mar 21, 2017 1:45 pm UTC

Bringing back the dead does seem a timely subject for this thread. = o
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Re: Minimum population question

Postby Writergirl » Sun Mar 26, 2017 11:55 pm UTC

It's a tad controversial, but many studies suggest that when Mt. Toba erupted 70,000 years ago, world human populations fell to the low thousands. The ice age also hit us pretty hard, seeing as we don't have fur. Those two disasters are why humans have such low genetic diversity today, compared to other apes. There is an oft-quoted factoid that two groups of the same species of apes in the same jungle have more genetic differences than all of humanity. So, whatever the magic number for a sustainable population is, it probably could've been lower if there hadn't been an ice age recently, or if we'd evolved to stay warm better.


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