This must have been the default for human history probably as well, I am thinking.

They also said the switch to putting babies back side down (as opposed to stomach side) had something like a 50% decrease in SIDS in the US.

I'd wager that for most of human history at least three generations lived in the same room.

I’m not sure. Biblical accounts seem to indicate everyone had their own tent. Granted, these were rich patriarchs, so maybe not the norm back then.

Is anyone here familiar with the subject across ancient cultures more broadly?

Personally, I sleep better when I’m alone. Haven’t convinced my wife that we should have a separate king and queen suite, though.

Not ancient, but I come from indigenous folks that live Southeast Asia. Because we're from up high in the mountains, the traditional way of living is supposed to go back quite far in time.

There are still a few that live traditionally in what basically is a large, two-floor long house for a multi-generational household. The families live on the second floor in one large room, but often with a small loft area for a quasi-third floodr The bottom floor is open with no walls (just support beams) to keep the animals. So it's constantly noisy.