Inequality has been linked to human sustainability for over 10,000 years, according to new findings by archaeologists.

Wealth inequality began shaping human societies more than 10,000 years ago, long before the rise of ancient empires or the invention of writing. That’s according to a new study led by Washington State University archaeologist Tim Kohler that challenges traditional views that disparities in wealth emerged suddenly with large civilizations like Egypt or Mesopotamia. The research is part of a special issue of the Proceedings of the National Academy of Sciences, co-edited by Kohler and Amy Bogaard, an archaeologist at Oxford University in England.