Inbreeding In Small Populations

[SaxonViolence]

Maybe this is more of an Anthropological Question.....

 

Please move if appropriate.

 

I recently read that most inbreeding problems could be side-stepped with a population of 1200? 1500? {Don't remember exactly.}

 

This applies mainly to Space Colonies. It could also apply to PAW {Post Apocalyptic World} Ark planning, etc.

 

Just for arguments sake, lets go with the larger number.

 

We start a Moon Colony, an O'Neil Colony--or whatever.

 

We hope there will be a steady influx of new Blood--but we want this Colony to be as Absolutely self-sustaining as possible.....

 

Even if they never get another shipment from Earth.

 

We start out with 1500 men and women, carefully selected to have above average Health and Intellegence--and screen out every genetic anomaly that it is possible to screen for.

 

Assume that for the first few generations, the Colony will be in "Go-Forth-and-Multiply", or Growth mode.

 

Couples will Average 4.5 Surviving Children between them.

 

But we want to stack the odds a bit more.

 

The Colonists bring along a very large assortment of Frozen Sperm from the best candidates available.

 

It is customary--though not strictly required--that each woman bear one child via Frozen Sperm before she marries.

 

Each Sperm Donor sires only one child. {Though there may be Multiple Specimens--for failed attempts, or unforeseen fertility problems.}

 

{To avoid the Inequity of every man being expected to raise one non-related child--AI Children are generally raised by the Mother's parents.....}

 

This is in addition to the customary 4.5 Children per couple.

 

A women who wants more children, or whose husband was infertile might chose to raise many more AI Children.....

 

As well as Women who never wed.

 

How much are we sweetening the gene pool?

 

A second question:

 

While I realize that Inbreeding is largely a matter of bad recessives piling up.....

 

Nonetheless, if our Colony was composed of Nigerians--just for instance--would a Sperm Bank collected from Norwegians, Taiwanese, Esquimaux and Navajo be more efficient at warding off Inbreeding, than a comparable Stock of Nigerian Sperm?

 

Saxon Violence

[Guest MacPhee]

A Nigerian Moon Colony would greatly stimulate space-travel. We'd be regularly launching rockets carrying "Earth Aid" to provide the colonists with food.

Edited June 17, 2012 by MacPhee

[CraigD]

I recently read that most inbreeding problems could be side-stepped with a population of 1200? 1500? {Don't remember exactly.}

 

This applies mainly to Space Colonies. It could also apply to PAW {Post Apocalyptic World} Ark planning, etc.

 

I recall at least some serious study of this question, ca. 2002, by anthropologist John Moore. As best I can tell, all or most of it was published in an obscure 2003 hardcover-only book, Interstellar Travel & Multi-Generational Space Ships. Though I can’t find an online source of the full book, excerpts, or preprints or academic papers of its source material, a couple of 2002 articles mentioning Moore and the subject. Whitley Strieber’s (I know, he’s at times a pseudo-scientific arch crank/provocateur, but he’s smart, and a good researcher) Love & Marriage in a Space Colony, and the NewScientist article "Magic number" for space pioneers calculated appear to have had access to it, and provided a bottom-line summary of Moore’s answer to the minimum viable population question for humans:

 

"160. But with some social engineering it might even be possible to halve this to 80."

 

It’s thought that the human population has fallen as low as 12,000 to 2,000 in the distant, prehistoric past, setting an empirical upper limit on the human MVP. (see here for a summary and some links to sources).

 

Nonetheless, if our Colony was composed of Nigerians--just for instance--would a Sperm Bank collected from Norwegians, Taiwanese, Esquimaux and Navajo be more efficient at warding off Inbreeding, than a comparable Stock of Nigerian Sperm?

I believe that, as a rule, present day geneticists are mistrustful of categorizing breeding stock by superficial appearance, nation of residence or family origin, etc, concluding that, even millennia before the 20th century’s great increases in worldwide travel and relocation, the human gene pool was so thoroughly mixed that there are practically no races, in a genetically meaningful sense. That is, a person who comes from a distant country and looks little like you may be more closely genetically related to you than someone a close neighbor who looks much like you. What we can see with our naked eyes can be deceptive.

 

To select a population, such as for a generation ship or a Moon or orbiting colony in solar system, if genetics were a primary criteria (there’s no guarantee, IMHO, that it would be – money, national interests, etc. are all possible, and not unlikely, non-scientific criteria), I think each candidate colonist, sperm, or egg donor, would be analyzed by sequencing and mapping all or part of their genome.

[SaxonViolence]

Well,

 

When the population fell, there may have very well been Some problems with Inbreeding--though obviously not insurmountable.

 

Then as the Population multiplied and split, enough point mutations would occur, to "Un-Inbreed" the Stock.

 

Was reading a book about Cheetahs sometime ago. Apparently, in the last Ice Age, Cheetahs all but perished, and today there is precious little genetic diversity amongst them.....

 

Resulting in Hiss-Poor fertility.

 

How so?

 

The Uterine Wall's response to a Fertilized Egg is very much like an Immune reaction to a Foreign Substance--at least in the initial stages.

 

The closer the Ovum's DNA is to the Mother's, the harder it is to get the Ball Rolling.

 

Are Racial Differences Skin-Deep {Only}?

 

Perhaps, I really don't Know--but in the current Climate of Rabid Politikal Korrectness, Researchers get Pilloried for even asking Questions--never mind the Conclusions.

 

Saxon Violence

 

 

 

Naive Mendellian Genetics seems to imply that from one parent, one either inherits half Grandpa's Genome, Or half Grandma's.

 

This is true for individual genes, but one's DNA doesn't stay neatly divided, Mother's Side to the Right; Father's Side to the Left.

 

The DNA crosses over at many points--therefore a given Sperm or Unfertilized Egg can have a virtually unlimited combination of Genes from Grandpa and Grandma.

 

This being the case, you can have true full Brothers who have less DNA in common than many first or second--or even far more distant Cousins.

 

{Can have--Obviously, that would be exceptional...}