"Comparing to Earth, Ark should carry a maximized human diversity. However, it is undoubtedly necessary to imagine that the settlement is done primarily by natural growth. The initial settlement, carrying out the way Ground-Ark could include as few as 2,000 families or 5,000 people, adults and their offsprings, knowledgeable in fields useful to construction and maintenance of the structure and the engines. And for the successor, a “meritocratic” ascent formed of volunteers selected for their social utility within the framework of the project.
The time of acclimatization and demographic balancing, including the possibility of a return to Earth, will undoubtedly be higher than a century." (http://strangepaths.com/interstellar-ark/2007/02/14/en/