If moral universalism is true... How would we actually investigate it?

I've been thinking about this less as a metaphysical question and more as a methodological one.

Most of the debate is stuck on "is there a universal root system or not." But that might be the wrong starting point. We're not working from a complete record. What survived is filtered by who had writing, who had power, whose traditions got preserved. The avg person's inner life in 3000 BC is basically inaccessible to us. Some of the deepest excavations may be the ones we've lost entirely.

So instead of asking whether the root system exists, i'm more interested in: given what we do have, what patterns emerge when we stop treating traditions as separate and start treating them as partial maps of the same territory? Where do the maps overlap? Where do they diverge in ways that are hard to explain by shared constraints alone?

That feels like a more honest investigation than trying to prove or disprove universalism from the armchair.

What would that kind of comparative methodology actually look like? And has anyone tried to build it seriously?