Human minimal viable population size

[Linda]

This is just something I am researching for a story and I find the topic very interesting. If a group of people (I have about 200) are stranded on an M class planet, could the group survive down the centuries? And would they have to have planned matings to keep the group viable? It seems like a group of 200 might just survive. Also would their sheep, sehlats, and dogs survive - assuming their breeding was supervised by the people, I would think so, and with smaller numbers of individuals too, I would suspect. Hey, you only need two rabbits to be inundated in no time. I didn't put rabbits on the ill-fated ship, but I am thinking about it.

You spotted the sehlats? Yes, there are Vulcans on this ship (about half of the people). Which poses the question of how they get over the interspecies viability problem - which they would have to keep this group going. Well, they do (though it may stretch your credibility under the circumstances). I gloss over it somewhat mainly because D.C. Fontana did in her novel Vulcan's Glory, but still try to give a plausible answer. If she (the inventor of Sarek and Amanda) can do it, so can I!

http://answers.google.com/answers/threadview?id=378894

[evcake]

Are you reworking Tides of Space? Color me anticipatory.

[Linda]

Yes! You read my mind! And adding a sequel of about equal length, which is half written at this point. I want to make the details more realistic.

[evcake]

Then this should be in the Happy News thread. IMO

[blacknblue]

Survive? I would say yes. Survive without serious issues with mutation and genetic drift? Depends on how ruthless they are willing to be about culling their population.

[Distracted]

The main issues would be with consanguineous matings in the 2nd and 3rd generations. Assuming a large genetic difference between Humans and Vulcans and a decreased live birth rate between mixed species pairs, the actual effective breeding population might be considerably less than 200, though. If you're dealing with, say, a population of 100 humans and 100 Vulcans, each 50% male/female, and the fetal loss rate is really high for mixed pairings, you might effectively be dealing with two populations of 100, one Vulcan and one human, if mixed infants rarely survive. This would narrow the gene pool. Still, if crossbreeding could be made possible then recessive defects would be less common, since a Vulcan and a human would be highly unlikely to possess the same defective gene to pass it on to their offspring. In a situation like that, crossbreeding would actually increase the longterm genetic viability of the population.

[blacknblue]

But as Dis pointed out, by the third generation inbreeding would be almost unavoidable. And there would be effectively no way to predict what kind of effect inbreeding would have on a mixed-breed population. What happens when you inbreed a half-Vulcan with their Human first cousin for instance? Or vice versa? Or their Vulcan double-second cousin reinforced from both sides of the family? Who knows?

Polka-dots?

[Kevin Thomas Riley]

I recently saw a documentary on the Discovery Channel that said we (humans) all all descendants of a really small group of people that crossed from Africa to present-day Yemen. Well, apart from the ones that stayed in Africa anyway (excluding those Africans that stayed behind but who were related to the ones that left). The "racial" distinctions (skin colour, slanted eyes etc) came later as people adapted to different new environments. That means that two persons that on the surface look very different could have more genes in common than two persons that look very much alike.

So I'd say quite a small population would in theory be able to multiply and populate an entire planet.

[Distracted]

The problem is the sharing of recessive genes. If two people are alike enough genetically, eventually they may each give a recessive gene to one of their offspring which, combined with the same gene from the other parent, could produce a serious genetic defect. So, the farther apart genetically two parents are from each other, the less likely they are to have defective offspring. I would think that a dual species population capable of crossbreeding would have a better chance of long term survival than a more homogeneous population simply because of its greater genetic diversity.

[Kevin Thomas Riley]

^ Well, obviously! Still, it seems we humans were indeed able to inherit the Earth from a rather narrow gene pool to start with. As to how many original individuals we're talking about, I suppose that's anyone's guess.

[Distracted]

Yeah, well, "survival of the fittest" no doubt did some culling for us as well. Major defects didn't survive to breed. The ones that DID survive lived only because the defect created a different survival advantage. Did you know that people with sickle trait are less likely to die of malaria?

I doubt a group of civilized humans or Vulcans could cull as effectively as Mother Nature. I have read stories where a limited population survived to colonize a planet and only allowed certain people to breed based on DNA compatibility studies. That would seem cold blooded to me, though.

[justTripn]

It sticks in my mind that in the bottleneck, was it 60,000 years ago, the population of humans was just 10,000? They were in East Africa.

I'll go google . . .

[justTripn]

I was about right according to Wikipedia. But look at this, also from Wikipedia on "Population bottleneck":

Animals


Wisent, also called European bison, faced extinction in the early 20th century. The animals living today are all descended from 12 individuals and they have extremely low genetic variation, which may be beginning to affect the reproductive ability of bulls (Luenser et al., 2005). The population of American Bison fell due to overhunting, nearly leading to extinction around the year 1890 and has since begun to recover (see table).

A classic example of a population bottleneck is that of the Northern Elephant Seals, whose population fell to about 30 in the 1890s although it now numbers in the tens of thousands. Another example are Cheetahs, which are so closely related to each other that skin grafts from one cheetah to another do not provoke immune responses, thus suggesting an extreme population bottleneck in the past. Another largely bottlenecked species is the Golden Hamster, of which the vast majority are descended from a single litter found in the Syrian desert around 1930.

[Kevin Thomas Riley]

I doubt a group of civilized humans or Vulcans could cull as effectively as Mother Nature. I have read stories where a limited population survived to colonize a planet and only allowed certain people to breed based on DNA compatibility studies. That would seem cold blooded to me, though.

We're talking about Vulcans here. They might say "it's only logical" and go on about their "cold-blooded" business!

Hm, that might actually make an interesting story. The Vulcan on the planet suggests this but the humans thinks it would be cold-blooded. Conflict ensues and voilà... a story!

[blacknblue]

Aside from recessive defects, what about lack of adaptability? Europeans tend to be chunky, furry, and pale. So what happens if the planet they land on has high UV radiation levels and all the Humans in the group are of European descent? Or suppose it has very low sunlight, and every Human has dark skin? Vitamin D deficiency would be endemic. Genetic diversity provides a safety net for changing conditions. What happens when you hit a streak of freakish weather, like the blizzard of 1978? Some of us were better adapted to survive that than others. Those of us who were better suited to withstand the conditions jumped in to help out the ones that weren't, and most of us made it through. But if we had all been desert or tropical jungle bred, it might have been a lot worse than it was.