“In cultures that lack writing, all individuals participate in the communication life of the group without need for special training or skill. Once writing is introduced, a hierarchy of political power becomes possible with the more skilled readers and writers holding a greater share of the power. Abstract concepts such as property, law based on principles, religion, and money are all introduced into a society along with writing.”
I wrote this about 10 years ago. In the United States, it seems this is not as true as it was then. In general, the trend continues; those with greater reading and writing skills do tend to have more power. It seems, however, the ability to for critical thought that was once associated with literacy has been lost. I expect it is temporary, and just like climate change continues despite it being cold in the winter (in the northern hemisphere) the powerful will continue to be those who have greater literacy and critical thinking. And creativity. And compassion.