I was wondering if one theoretically wanted to start a new cizilazation
or colony somewhere, what would be the minimum number of people needed to
insure that there will no inbreeding? This assumes that there are no frozen
eggs or sperm or other such external aids. I know that royalty used to breed
within their lineage to keep the blood pure, but I also read that this lead
to a higher rate of children with health problems.
Royalty back in the day also didn’t have access to modern medicine and vitamins. Was it the inbreeding, or was health reasons in general? Probably GD territory…
There’s some interesting info here.
Also, I think it all depends on the genetic health of your colonists. The only reason that inbreeding is so unhealthy is all of the damaging rare recessive genes. If you could screen large numbers of people for these rare genetic disorders before picking your actual colonists, and we now can, you’ll be able to reduce that number a fair bit.
Well, genetics certainly played a role in the hemophilia. There’s no doubt that the small gene pool affected the royal lines.
But to answer the question above–it would depend on what your criteria are for “minimum required”. Theoretically, two sets of genes would be adequate…Or even one full set of chromosomes plus just one extra “X” or “Y” to give you genders. (Assuming we’re talking humans).
As long as there were no lethal equivilants in the bunch, everyone would be exactly the same but the civilization could grow. The risk is that with no genetic variability the group would be at high risk from disease and whatnot.
Inbreeding does not create genetic diseases - it merely makes it more likely that recessive conditions will be expressed. If you happen to have a rare recessive mutation, and you have children with some random person in the population, the odds are very small that that person will also have that mutation (since it’s rare), so you’re not very likely to have a child with two copies of the mutation. But if you marry someone related to you, the odds are much higher, since you know that that mutation is present in your family. That’s why inbreeding is a problem.
Now, if you look hard enough, you could almost certainly find at least one mutation in every family that would cause a problem if it were present in a homozygous state, so inbreeding in general is problematic.
But if you had some idealized population with no harmful mutations at all that was protected from any external mutagens and somehow had a 100% faithful DNA replication system, you’d never have a problem with them inbreeding.
Or a psycho-social mess, for that matter. I’m curious about this too… if humanity ends up surviving the death of the solar system, it’ll be by colonizing other worlds far from here, so we’d better choose our settlers carefully!
I don’t think this sentence means what you think it means. Perhaps you mean to use the word inbreeding instead of genetics.
If so, then you are incorrect. Inbreeding had nothing to do with the hemophilia that occured in Queen Victoria’s line. The hemophilia would have been the same whether Vickie had married her cousin or an Australian aborigine or anyone else whether they were closely related or not.
I think Cecil may have covered this in one of his columns, but the Search Archive page is misbehaving right now (it keep wanting to download a file rather than bring up the search entry page) so I can’t be sure.
Previous thread.
It really does depend on how strict you in enforcing fidelity in marriages, how fast your populationis able to multiply and so forth. The absolute maximum required would be 5000 since we know that humans have survived isolated for millenia with that few people.
In reality you could probably get away with it with less than 20 people if you were prepared to keep stringent genealogy records and the populaiton was growing rapidly,
Well, I know that Huterites can all trace their blood lines back to a pool of 60 people. I know that they also have genetic problems cropping up at a greater rate than the general population.
However, I’m assuming they wern’t chosen for their fabo genes, back in the day, although they were pretty much all solid German breeding stock, so there you go.
I supposed if you could live with a somewhat increased rate of genetic blips, then 60 would be OK.
No…I meant that genetics played a role in the hemophilia. That is, hemophilia is a genetic aberration. But I understand what you’re saying: that inbreeding did not lead to the expression of the mutation in this case.
Anyway, with regards to the original query, genetic bottlenecks have occured and been survivied by as few as 20 individuals (cite ):
Several examples of bottlenecks have been inferred from genetic data. For example, there is very little genetic variation in the cheetah population. This is consistant with a reduction in the size of the population to only a few individuals - an event that probably occurred several thousand years ago. An observed example is the northern elephant seal which was hunted almost to extinction. By 1890 there were fewer than 20 animals but the population now numbers more than 30,000. As predicted there is very little genetic variation in the elephant seal population and it is likely that the twenty animals that survived the slaughter were more “lucky” than “fit”.
Another human example.
So the question you’re looking to have answered in the case of the health of a population is really how many individuals does it take to maintain good genetic variability and avoid a bottleneck? It’s been a long time since I’ve done any population genetics (See Hardy-Weinberg Principle) but as others have stated above a few thousand individuals are probably the minimum. It’s really a curve, with variability dropping off rapidly as the numbers dwindle.