For most of our evolutionary history, we humans have been living in small groups, with no more than a few dozen up to a hundred people. Any life in groups brings with it the potential for conflict and the challenge of how to distribute resources or how to make decisions.

We have evolved social behaviors that enable us to regulate social life in such small groups, including social emotions, a social temperament, moral intuitions such as a sense of fairness and a sense of liberty and autonomy, and a so-called norm-psychology – a tendency to learn and imitate the behaviors of the people around us, to consider these behaviors as “normal” and to be irritated if someone behaves in a way that doesn’t follow the group’s norms.

Today’s hunter gatherers give us some clues about the social organization that our species lived in throughout most of our history. Hunter-gatherers tend to live in egalitarian groups, meaning that there is no strong hierarchy and an equal distribution of resources. Attempts by individuals to dominate the group or hord resources are discouraged and punished by everyone else in the group.

However, with agriculture, the ability to store and accumulate valuable resources, division of labor, the first cities, our group sizes started to grow, from a few thousand to many thousands and finally millions of people. How can life in such groups be regulated? It seems that with the increase in group sizes, the leveling mechanisms that worked well in small hunter-gatherer groups did not work sufficiently anymore in such larger group, and with increasing group size came an increasing inequality in power and wealth.

Scientists are trying to better understand the factors that have lead to this departure from egalitarian hunter-gatherer origins and the spread of inequality throughout our history.

One such factor seems to be the ability to store, accumulate, and defend valuable resources, which became possible and important with the beginning of a sedentary lifestyle and agriculture. Another factor seems to be the inheritance or transmission of these resources to children (instead of redistributing them equally to everyone in the next generation). Whether or not wealth is inherited or redistributed in the population, and to what extend, is governed by more or less formal social norms and institutions (such as property rights, tax regulations for different sources of wealth, existence or absence of social welfare programs such as funding equal access to education and health care for all citizens).

These factors together led to a transition to greater inequality in the neolithic period, and to an increase in inequality over time, through a feedback loop – the more wealth someone has, the more access to power and education they have, and the more wealth they can accumulate (and transmit to their offspring) (see also: System archetype “Success to the Successful”). Over time, the rich get richer, and the poor get poorer.

However, in the last two centuries, there is also a decrease in inequality observable.