Life after the apocalypse is perhaps one of the most popular genres of fiction and cinema. According to the Abrahamic religions, in order to revive humanity in such cases, only two people are enough for nature: a man and a woman. But is it really so?
How many people do you need to guarantee the population of the entire planet?
According to the experience of livestock breeders, in order for a population to survive and reproduce successfully, it must contain at least 50 healthy and mature individuals, based on 25 females and 25 males. This condition also applies to humans.
The main problems of such a small group of “founders” will be the degeneration of genes and inbreeding. The point is that 50 individuals cannot carry the entire genetic diversity of mankind. Part of the signs (for example, blood type, skin color, certain physical and mental abilities) will be lost.
In addition, in such populations, the likelihood of inbreeding depression is high. This is the result of closely related marriages, not necessarily in the first generations. In a group with the same alleles of genes, offspring can inherit recessive traits.
Under normal circumstances, the mother and father give the child two sets of identical genes. If one of them is damaged, then the embryo successfully replaces it with the second. However, if the defective set of both parents is identical, then the child will have a spoiled hereditary factor.
At best, this will weaken its immunity and biological adaptation, at worst, it will reduce reproductive abilities or lead to death.
To prevent this from happening, the optimal number of individuals in a group should not be less than 500. In science, this is called the effective population size. Its range is the same 50/500 individuals. Here, 50 individuals is the minimum threshold and 500 is the preferred threshold.
Planet colonization and modern technologies
US anthropologist John Moore calculated the number of people needed to colonize a new planet. The scientist suggested that if technology will allow us to move to a new planet, for example, to Proxima b, then the crew of the spacecraft should be 180 people carefully selected for genetic characteristics.
These are young healthy people who will be forced to track marriages among themselves.
Anthropologist Cameron Smith disagrees. John Moore does not take into account accidents and the psychological factor. What if one of the crew dies? But what if such a factor as love intervenes in the selection? Then the whole mission will be in jeopardy.
It is best to send not 180, but 14,000 young people. This colony, given the resources, will survive anyway.
The problem seems completely insignificant if the crew does not reproduce naturally, but with the help of genetic engineering and an artificial womb. Then the crew can safely be the aforementioned 50 people.