A big family has cultivated fruitful soil; two little families nearby have thankless and rebellious fields. The two poor families have to serve the opulent family, or slaughter it; there is no difficulty in that. But one of the two indigent families offers its arms to the rich family in exchange for bread, while the other attacks and is defeated. The subservient family is the origin of the servants and the workmen; the beaten family is the origin of the slaves.
─ Voltaire (from "Equality," Philosophical Dictionary, 1750)
This is a web-based version of the simulation described in this seminal 2006 paper by anthropologist Eric Alden Smith and economist Jung-Kyoo Choi. The paper presented a rigorous simulation of a theory of inequality that philosophers, social scientists, and economists have been refining for centuries.
The simulation creates a world of dot people born into patches with various amounts of resources (greener = richer). All dot people reproduce at a rate proportional to their income. A dot's income is displayed as the size of the dot, and you can set the rate of proportionality with the slider. There are different types of dot people: Doves, Solos, Clients and Patrons, who have different ways of getting income.
At first, all dot people are Doves. Doves simply share the resources with other dot people on their patch. When a new dot person is born, there is some probability (I keep it at 10 percent) that their offspring will have a different survival strategy. It might become a Solo — a type of dot that does not tolerate other dot people on its patch, and will pay a price to defend the patch. (You could think of Solos as the first dot people to discover the idea of ownership.) A dot person could also mutate into a Patron or Client. Patrons are territorial like Solos, but they engage in trade with Clients, giving up some of their resources for labor from the Clients, as long as it profits them overall (you can play around with the Patron's revenue from the Client with the slider). Clients are like Doves in that they are willing to share their patch, but they also engage in trade with their Patron.
Every year, every dot person reaps income from its patch, the Patrons and Clients engage in trade, and dot people are born and die according to their total income. It's a simple life, being a dot person.
Play around with it yourself and find out! But here's the gist: When trade is very profitable, Patrons and Clients generally dominate. When reproduction rates are high, Doves and Clients are prevalent, since they breed quickly enough to dominate the resources before territorial strategies can take hold. When reproduction rates are lower, but trade is not very profitable, territorial strategies (Solos or Patrons) will dominate.
Although the world is more complicated than these dotted fields, the recipe for inequality can be simple: ownership, trade, and a splash of luck. Fair individuals can unwittingly create unfair systems. It's important as we search for solutions for inequality that we think systemicly, not locally. So think kindly on your richer and poorer neighbors: they are just little dots like you, but born into a different patch.