Every once in a while they might come together with other bands, possibly in seasonal festivals at which they would share news and knowledge as well as giving young people the opportunity to find a mate outside their tiny community.
this is good sentence and explains that although prehistoric groups were usually small and isolated. they occasionally gathered with other groups. these gatherings likely happened during seasonal festivals. such events were important for sharing information and cultural knowledge strengthening social connections, and helping younger members interact beyond their small community.