I read a SyFy story a while back where a colony ship with hundreds of people aboard were going to a new planet.
None of the original were left, as it was taking a couple hundred years to get there.
The ones left had lost their ancestors’ level of knowledge and had separated into two ‘tribes’ each one cannibalizing the other, even though there was plenty of food stored aboard but they didn’t know how to open the storage bins.
They had lost all knowledge of the outside of the ship and thought that it was the entire ‘universe’. Kinda like the Easter Islanders....................
It’s about how it would go isolation leaves nothing.