So why so many people? The first thing to look at is that even the nearest star system, Proxima Centauri, is over four light-years away from Earth. At our current technology level, it would take us thousands of years to get there. This means we’d need to have a starship where generations are born and then die without ever seeing the planet that will eventually be colonized, not to mention the planet that they came from. 150 people could probably handle that, but there would be very little genetic diversity, which could increase susceptibility to genetic diseases. In Moore’s study, a larger number — at least 10,000 people — would ensure viable diversity in the human gene pool.