Even in the ancient world, wealth was represented by the size of your home, according to a new study.

The study, published this week in Nature, found that the introduction of agriculture sparked a rise in inequality between the “haves” – large-scale farmers – and the “have-nots” – landless workers.

Researchers from 14 different institutions collected house-size data from 63 archaeological sites, or groups of sites, in North America and Eurasia dating from before 8000 B.C.E. to around 1750 C.E. The team had to rely on house size due to the lack of detailed economic records from that timeframe.

The team used the data and a standard measurement of inequality known as a Gini coefficient to calculate the distribution of wealth in specific societies.

Gini coefficients, developed by the Italian statistician Corrado Gini, range from zero to one. Zero represented a society with complete wealth equality, while a ranking of one means a single person obtains all the wealth.

The researchers found that hunter-gatherer societies had low wealth disparities, with a median Gini of .17. They noted that the mobile lifestyle of hunter-gatherer groups made it difficult for individuals to accumulate wealth.

The introduction of agriculture led to designated social classes. Horticulturalists (small-scale, low-intensity farmers) had a median Gini of .27, while larger-scale agricultural societies had a median Gini of .35.

But, the researchers unexpectedly found that while societies in North America and Mesoamerica (the New World) plateaued at .35, inequality kept rising in the Middle East, China, Europe and Egypt (the Old World). Eventually the median Gini reached about .59 in these regions.

The researchers believe domestic animals may have been a main factor in the difference between the New World and Old World.

Old World farmers had the luxury of cattle, horses and oxen to do the labor of plowing fields, and carrying goods and people longer distances. This increased efficiency allowed farmers to expand and create larger plots, and stockpile foods. They also established groups of warriors to protect large territories and conquer new land.

The land and animal assets could also be passed down to future generations, allowing some families to accumulate even more wealth over time, while the poor struggled to do the same.

“These processes increased inequality by operating on both ends of the wealth distribution, increasing the holdings of the rich while decreasing the holdings of the poor,” the researchers write.

New World societies, however, didn’t yet have domesticated animals, and relied on human labor to accomplish tasks.

But, the researchers point out that the Gini coefficients seen in the Old World still do not even compare to modern day. The 2017 Allianz Global Wealth Report puts the U.S. Gini at .81. Previous estimates reported China at .73.