“Unregulated Capitalism” is the model that most closely describes the behavior observed in underground/black markets.

Yes.

It is the state that emerges when humans make the choice to engage in commerce without regulation: capital gets allocated according to the laws of natural selection instead of supply and demand

No. Commerce without regulation existed for millennia, as you have correctly addressed here:

Humans lived in stateless societies for longer than we’ve had recorded history.

The black market is indeed commerce without regulation. That's the unregulated part. But it isn't just that. It is also a hierarchical system with privately accumulating capital at the tops of a steadily diminishing number of pyramids - that's the capitalism part - with no overarching authority to regulate it. In short, unregulated capitalism.