This is scientific American 60 second science. I'm Christopher Intagiyata.

The square footage of a home tends to be a measure of wealth.

Compare the sizes of dwellings in a city, and you'll begin to get a picture of rich and poor and how wealth is distributed.

Now researchers have used that modern metric on ancient settlements.

They investigated housing-based wealth at 63 archaeological sites, from old world places like Mesopotamia to new world sites like Mesa Verde in Colorado.

As expected, the wealth differential widened as agriculture took off, and it kept growing in the old world.

But in the Americas, the gap suddenly stopped growing, about 2,500 years after the first crops showed up.

Well, this is a surprise, first of all.

Timothy Kohler is an archaeologist at Washington State University.

His team's hypothesis for the differences between hemispheres,

the old world had large domesticated animals.

And that, they say, was a game changer.

Because if you have a team of oxygen available, then you can farm much further from your house and you can also farm much more land and you can probably raise your income quite dramatically.

That sort of farming's land hungry, he says.

So over time, landowners with beasts of burden got richer at the expense of landless peasants.

The studies in the journal Nature.

Kohler says it's harder to scrutinize the holdings of the wealthy today in the age of

shell companies and offshore accounts, but he has this tip for future archaeologists.

My advice to them would not be to look just at their main residence, but if they have

residences in, you know, in New York City or in the Bahamas or wherever, they need to add up all those

residences and attribute them correctly to a single household.

Given the modern day stats on the wealth gap,

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