To extend the concept in the thread ‘Repopulation with 1 woman but multiple sperm donors’ further what is the viability of one woman who just had sex at restarting the species?
To all the complications and improbabilities in that thread, now other limiting factors are involved including 1 shot at pregnancy that must produce a male child and the woman must either still be able to conceive from her male child when he is old enough, or she must have twins of opposite gender from that first pregnancy. Also the inbreeding aspect should also be harsher then the other thread.
But is it actually possible though very improbable or is it impossible and there is no chance?
It’s not inherently impossible. Lab animals are routinely inbred to this extreme (so researchers can use a genetically homogenous population). But these critters aren’t very healthy even in the best cases, and wouldn’t stand a chance in the wild.
Basically, the problem is thus: every human have a handful of new mutations in their germ line, which they will pass on to their offspring. Most frequently, these mutations will be recessive, so they will never cause a problem when two unrelated individuals mate. But with inbreeding to this extent, some of that original handful of mutations will almost inevitably spread throughout the population, and genetic diseases will be common.
By comparison, the various royal families, with all of their genetic diseases, weren’t as inbred as a population your hypothetical case.
If the child is male - then the gene pool is 1.5 individuals. If they are fraternal twins (M, F, odds what - roughly 1 in 70?) then they will have approximately 50% genes in common. Combines with the mother, that makes 1.75 original individuals.
This would be risky. The problems with inbreeding is faulty genes - that often, faulty genes are “broken”. A gene that is supposed to make a particular (necessary) protein, does not. (I.e. in the sequence to make insulin, to make growth hormone, to make melanin, to make clotting factor, etc.) If a second copy of the gene is not broken, then that one may make enough of the protein that there is no problem; it is a recessive gene, but the healthy individual is still a carrier. Half his offspring will get the gene; if it pairs up with the same broken gene, the person will have problems. (Or, the mother will miscarry) If the gene codes a protein that disrupts the process in any way, it is a dominant gene and all offspring will have it.
Then, you have to rely on frequent mix-and-match to reduce the frequency of bad genes - but still, that means that say, one out of 4 genes in the pool is bad, the odds of deformities are pretty high. If the deformity is common, what would it be? How likely is a subsistence culture to tolerate individuals that are a burden on their resources? I sense a “harsh decision” story line…
I suppose that one story-angle advantage may be that those chosen to explore strange new worlds and seek out new civilizations probably are either chosen from the finest of the gene pool, or from a civilization advanced enough to weed out or correct such problems - although new errors can creep into the gene-copying process all the time.
If you look at the social implications of this situation, I think you’ll find it rare to the point of impossibility that the single survivor of the human race is going to concern herself so much with propagation of the species that she would have sex with her own son. More likely, they would either hunker down and try to be as happy as possible until they die, or spend their time traveling looking for other survivors to reproduce with–that is, if she even survives a solo childbirth.
If I were in such a situation, I wouldn’t concern myself with the future of the species. My child and my survival is the only thing that matters. The species is already extinct, as far as hypothetical me is concerned.
They don’t have to necessarily concern themselves with the survival/repopulation of the species, sex happens, and in such a situation contraceptives would probably be a bit hard to come by along with abortion services.
I believe there’ve been some islands colonized by a single pregnant female. However, these were in species where multiple births were the norm, rodents or rabbits or similar..
