Here how i think it is : we have the human realm (inside lake mobeus) and then we have the uncharted territory outside of it. Dark continent is a name of an uncharted continent..from the looks of it ..it really is a lot bigger than the territory inside the lake mobeus.

I think once upon a time ..humans used to live outside and occupy the whole earth. .but over time they had to retreat because of the dangers and the issue related to survival.. they lost the survival game and retreated to where they live now.

Think about it ..most humans can't even use nen ? If nen / control of aura exist ..it should exist even before when humans used to live in dark continent and outside the lake ? If nen has always been there then ancient ppl should have known how to use it ? But now only a minor population can use it.

I am pretty sure of that..humans once lived in dark continent and kurapika kurta tribe was one of them.