5
So this might be a slightly weird one, but I"ve seen answers to questions about minimum numbers for re-population and such, but what about a system where reproduction was controlled and coordinated, and the intent was zero population growth? The theory is, quite apart from sexual or romantic relationships, everyone in the group is the genetic parent of exactly two children (barring instances of twins/triplets/whatever), each with a different partner, so that everyone is genetically responsible for half of two children, and theoretically the closest relation anyone can have in their own generation is half-sibling, thus sharing on average only 25% of their DNA.
So how might a system like this impact the needed starting population size, assuming that eventual reintegration with a larger population was for practical purposes impossible? How many generations back does a common ancestor need to be to minimize the chances of undesirable effects of inbreeding? I know it would rely on a perfect, or near-perfect, 1:1 ratio of genetically female to genetically male, so I guess another question is how large a population do you need for the randomness of birth to reliably average out that way?
1Try narrowing this down to only one question. – callosaurus – 8 years ago
5Siblings share far more than 25% of their DNA with each other. There are worms that share 70% of their DNA with humans. – sphennings – 8 years ago
I think he more so meant Genes than DNA. – ggiaquin16 – 8 years ago
I answered below, but I realized that didn't answer the last part, so here it is: there is no reliable way to ensure averages in random processes. You will need to add this to your caveats... – adonies – 8 years ago
@sphennings And wasn't it chimpanzees who share the upper half of 99% of their DNA with humans? Something like that, though I wouldn't take poison on the exact number. – a CVn – 8 years ago
Check out some tribes that avoid contact with the outside world. Some exist for over 10 000 years with varying numbers, the lowest number I found was 15 individuals. The negative effects of inbreeding are vastly overestimated in our society – Raditz_35 – 8 years ago
Negative factors are not included in your model. But they happen
also note some models. They are different from you but could be useful
– ADS – 8 years agoYour premise is problematic. Mutations occur in our DNA all the time. It is a principle of genetics that without natural selection, deleterious mutations will spread in a population. Meaning in your scenario, as far as I can understand it, there never will be a "stable" population. You need to birth more than 1 person for each person in a population to maintain a stable population, and you need to allow for 'selection' (meaning competition, deaths and failures to reproduce). There's no established reason that the sex ratio must be close to 1:1. In fact it is not 1:1, (possibly as high as 1.2 – Soylent – 8 years ago
Giving you some pointers for further thought: https://worldbuilding.stackexchange.com/questions/3188/what-should-three-men-and-three-women-do-if-everyone-else-is-dead, http://www.telegraph.co.uk/news/worldnews/australiaandthepacific/pitcairnislands/1475509/We-sensed-a-dark-side-to-this-teetotal-God-fearing-little-society.html, http://www.sciencedirect.com/science/article/pii/S0006320707002534, https://en.wikipedia.org/wiki/Minimum_viable_population.
– adonies – 8 years agoAlso here: https://biology.stackexchange.com/questions/5524/how-many-people-are-required-to-maintain-genetic-diversity
– adonies – 8 years ago