The cartoon shows how early agrarian societies tended to trade in order to get basic goods they lacked in exchange for the surplus of the goods they had.
These societies realized that through commerce they could satisfy their needs more efficiently than remaining isolated. In this way, through specializing in one specific activity that cost less in comparative terms (due to their abilities or access to resources), like producing spearheads or hunting zebras, a tribe was able to exchange its surplus for the other goods it needed that was the surplus of another tribe. By doing this, both tribes increased their general satisfaction and got more resources than by trying to be self-sufficient.