from 120 people? You wouldnt have a viable genetic diversity for long term survival. inbreeding would quickly become a thing, and i doubt you’d make it to even 100,000 before total collapse.

For long term survivability, you’d need like…a minimum of 5000 people, and even with 5k you’d have to have strict controls on who could have children with who, for decently long time.

Well: if we believe Christianity we only needed 6k-10k years from two people to the billions we have today, so it shouldn’t take so long

The current consensus is that the minimum viable population for most species is between 500 to 1,000 individuals.

The problem isn’t inbreeding depression (you only need about 50 individuals to avoid that)—it’s lack of diversity to adapt to a changing environment. Pathogens would evolve that would wipe out the entire species because they’re too genetically homogeneous.