That's really interesting, but why are they only allowed to have one child each?
The population of 2000 gets halved over time, which is not good. And though the smaller populations (150 and 500) look as if they survived better, that's partially because those populations had to have looser birth restrictions: Whereas in the simulations, the larger populations were allowed to have only one child per couple, the smaller populations allowed a couple to have two or three children to ensure the survival of the community. In the end, the growth cancelled out the disastrous effects. And if we take a look at the original 10 simulations for the 150-person starship (see graph below), we can see that three of the populations were totally wiped out. For 500 people, only one population got wiped out, and the risk of a wipeout gets smaller as population size goes up. The takeaway is that for both factors (genetic diversity and catastrophe survival), bigger populations are better.
Doesn't that by default halve the population every generation?