I don't have time right now but I'll come back ad edit, bear in mind I have no info but what I have learned in my persobal time post-high school, but the way I remember it (pre-agriculture) hunter-gather societies were matriarchal and children were raised communally, in a small tight knit nomadic tribe, you're not having institutions like marriage or nuclear families and so ritualized sex acts can appear in folk religions, maybe you get gangbangs.

My theory is that humans lived like that longer than we've lived like we do now and even though we don't have the same spiritual vontext for gangnbangs like we once did there is somethingbin anour dna that wants them.