How many people does it take for our species to survive?
This question was asked by the journalists of the scientific website LiveScience. It turned out that the answer depends on the circumstances: different disaster scenarios are different conditions for the survival of the human population.
One of the most unfavorable variants of the apocalypse is nuclear war. It could trigger a nuclear winter, in which even summer temperatures will be below zero, and survivors will face imminent famine, not to mention radiation exposure. Nevertheless, if even a few hundred people manage to survive this, our species will be saved.
Anthropologists who specialize in the study of early human civilizations and space colonization know that groups of several hundred people can survive for centuries and even millennia. There are many examples of this in history. About 12,000 years ago, when the last ice age ended and the early Neolithic era began, there were many small villages in the world. They were inhabited by from several hundred to 1000 people engaged in agriculture. They probably had family and marital ties with the inhabitants of other villages of the same kind, but in general they were fairly independent populations. In an apocalyptic scenario, the same thing could happen.
In the event that human civilization is destroyed, residents of large cities will find themselves in the most vulnerable position: they are completely dependent on imports of food and electricity. Therefore, the surviving populations will be forced to disperse in search of resources. One of the main problems in this case would be inbreeding - crossing of close relatives. For small populations, this is always a risk, an example of which is the fall of the Habsburg dynasty. Closely related marriages, which members of the royal family practiced for centuries, led to the fact that their last representative, the sick and sterile Charles II, in the sense of genetics, was the fruit of an incestuous relationship between brother and sister.
The same threatens the survivors of the apocalypse if they do not have the genetic diversity to avoid closely related alliances. In addition, for a successful crossing, a certain number of individuals of the opposite sex of childbearing age are required. This is the so-called effective population size - the average number of individuals in a population, the genetic contribution of which ensures its successful reproduction and survival.
It would be more real to survive a global catastrophe if humanity seriously prepared for it. For example, it would build shelters where it would be possible to isolate from the source of danger. Let us recall the island states of New Zealand and Australia, which, with the onset of the coronavirus pandemic, turned into a kind of large-scale shelters, isolating themselves from the rest of the world and preventing the spread of the virus on their territory. Another example is the World Seed Vault on Svalbard, where seed samples of major crops are hidden in a tunnel at a depth of 130 meters. Experts believe that it makes sense to create such a special shelter on Earth in case of disasters and for people.
Another scenario is when all that remains for people is to leave the Earth. What size team is needed to survive in space? Experts in space anthropology have calculated that a launch crew of 98 would be enough to reach Proxima Centauri b. It is the closest known Earth-like and potentially habitable exoplanet. It revolves around Proxima Centauri, the closest star to the Sun, and is 40 trillion kilometers from us. At the current level of development of space technology, such a journey will take 6300 years.
At the same time, it is necessary that the crew consists not of random people, but of 49 unrelated couples capable of reproduction, and childbearing must be controlled and limited so that the population remains genetically diverse and healthy. And a very good option would be a crew of 500 people - with such a number, the probability of preserving the genetic diversity of the population would be much higher.