Was reading about the Taino people that met Columbus, and how the chiefs could have as many as thirty wives or husbands and how they were often carried on palanquins by four other men, and wondered this.
I think this question would be more appropriate for an anthropologist or archeologist to answer than a historian as there are no known historical records of the first agricultural societies. The first known writing systems (roughly 3500 BCE 1) don't pop-up until several thousand years after the first large scale agrucultural communities began. "The first agriculture appears to have developed at the closing of the last Pleistocene glacial period, or Ice Age(about 11,700 years ago)." 2
Thus any evidence from this time would have to come from the archeological record or cultural studies.
The reason why these chiefs had so much power was probably resource control. The person, family, or tribe with access to the best resources would have wielded considerable power in these ancient societies. "Chiefs and their families generally have a higher standard of living than ordinary people. What makes this possible is that chiefs usually perform a society-wide economic redistribution function that, in some cases, is cloaked in the guise of ritual gift giving." 3
Edit: Apologies for bad formatting, done on mobile.