Think of it in terms of thermodynamics. The first group requires extra energy relative to the second group to perform roles of leadership, since those are secon

Think of it in terms of thermodynamics. The first group requires extra energy relative to the second group to perform roles of leadership, since those are secondary goals. The second group is instead naturally drawn to the roles of direction of the group. Thus, the lowest energy state will be one where the second group is in charge. Over time, things will gravitate to that state as it is the global minimum.