It fits "just so" like a lot of evolutionary biology hypothesis but it does seem that there would be an advantage to have some portion of the population that sp

It fits "just so" like a lot of evolutionary biology hypothesis but it does seem that there would be an advantage to have some portion of the population that spent a significant part of their waking hours after dark. People to keep the fires going, to keep away predators, warn the rest of the group of danger, etc.