During settlement planning, if the human population is to reproduce, careful consideration into the size of the starting population must be carried out. The size of the human population must not be too small due to the risk of Inbreeding Depression (causing genetic disorders) and it must not be too big due to the risk of overpopulation (causing lack of food/resources).
Statistically, every person owns 5 to 6 genetic defects, each usually only on one of two chromosomes in a pair, preventing clinical manifestation. The combination of two identical defective DNAs poses a 25% probability to result in a DNA with the same defect on both chromosomes, which inevitably causes some kind of disability.
- To achieve large genetic diversity a possible solution is to bring a few adult colonists and many fertilized human eggs to Mars. This gives an opportunity to build a big community on Mars with a comparatively small transport effort. (inspired by The Cascade)
- Genetic screening and selection of the settlers who are going to Mars. If the settlers do not carry any genetic defect, the inbreeding depression does not occur, no matter how small the population is. The problem is: Not all defects are known. Only a small number can be detected with today's knowledge, but that knowledge is supposed to increase rapidly in the next few years.
- Another solution is to rapidly increase the gene pool with a high level of immigration. With this scenario there is no inbreeding because the population is too large and diverse. This solution requires low transportation costs or a vigorous colonization program, or both. This must go hand in hand with a great increase of food production, to avoid overpopulation. And eventually require a lot of energy. A case can be made that available energy is the most important driver for population and therefore for avoiding inbreeding.