According to Popular Mechanics, it was originally believed that to successfully colonize another solar system, you would require a minimum of 150 colonists who, along the 2,000-year journey, were careful not to inbreed. Now it turns out that the minimum requirement is actually 10,000 colonists, with 40,000 being the ideal number, just in case there were several casualties along the way.
Genetic diversity keeps groups healthy, and larger populations tend to have more diversity. In small or isolated groups, including Ashkenazi Jews and the Amish, marriage between relatives has reduced genetic diversity and made otherwise rare diseases such as Tay Sachs and cystic fibrosis common among those populations. Graph A shows that Moore's suggestion of 150 people is not nearly high enough to maintain genetic variation. Over many generations, inbreeding leads to the loss of more than 80 percent of the original diversity found within the hypothetical gene.
A population of 500 people would not be sufficient either, Smith says. "Five hundred people picked at random today from the human population would not probably represent all of human genetic diversity . . . If you're going to seed a planet for its entire future, you want to have as much genetic diversity as possible, because that diversity is your insurance policy for adaptation to new conditions."
A starting population of 40,000 people maintains 100 percent of its variation, while the 10,000-person scenario stays relatively stable too. So, Smith concludes that a number between 10,000 and 40,000 is a pretty safe bet when it comes to preserving genetic variation.
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