Animal migration?
Which if you think about it makes a lot of sense for a evolutionary explanation for this behavior.
The existence of night rhythm people is hypotized to be a genetic factor that a human group needs some people to guard at night to keep the fire going and everyone safe.
Having a person within your group capable of noticing and tracking patterns trough time in nature can be a huge benefit but there is little further advantages to have more/multiple people tracking the same things.
Our genetics never considered that one day we function in a mega society where most people we interact with don't even know our full name, let alone our divergent skills and personal (dis)advantages.