The gulf between the haves and have-nots was smaller in the ancient Americas than in Eurasia.

After the advent of farming, inequality rose more dramatically in Europe and Asia than in the Americas.

Efforts to measure wealth in ancient societies are complicated by a lack of written records and the difficulty of linking expensive burial goods to specific households. Timothy Kohler at Washington State University in Pullman, Michael Smith at Arizona State University in Tempe and their team used house size — which often stands the test of time — as a proxy for household wealth. Studying sites across Europe and Asia dating between 11,000 and 2,000 years ago, and in North and Central America from 3,000 to 300 years ago, the team found that inequality increased worldwide over time, especially after the rise of agriculture.

Disparities were bigger in the Old World than in the New; this might be explained by Eurasia’s abundance of large domesticated mammals such as oxen and horses, which provided transport, farm labour and valuable manure. The services provided by these beasts might have made farming more profitable and enabled wealthy farmers or warriors on horseback to amass large amounts of land, the authors suggest.