The trick is not have "wealth" (ie property ownership/rights). Societies that were nomadic with low/no property ownership culture did not have wealth inequality since there wasn't that much "wealth" to have. They had their hierarchies but those were weak, more akin to the kind of hierarchies you have in families ("everyone listens to grandma" kind of hierarchy). Wealth inequality is obviously synthetic (and this study is kind of silly), since you need a governing body to maintain property rights (along with creating what today are the most valuable legal ownership structures, like intellectual property). A corporation, a mortgage, a deed, equity, all the defining elements of wealth, are exclusively legal constructs created/administered by governments. The wealth of every wealthy person you can think of is based on their rights to property, not the property itself (i.e stocks, deeds, trademarks, copyrights etc.). This requires a very elaborate infrastructure to maintain and a culture to support it. Wealth isn't a given and actually is very easily destroyed (when governments are toppled or property rights are taken away--Communist rebellions of the twentieth century are a good example).