Why class societies are rule, not exception

STANFORD (US) —The disproportionate suffering of the poor may have been a driving force behind the global spread of class structure during early human civilization, according to a new study.

Using a computer simulation to compare demographic stability and rates of migration for both egalitarian and unequal societies, researchers found that class structure provided unequal access to resources, contributing a destabilizing effect on the population, and driving migration and the expansion of stratified societies.

“This is the first study to demonstrate a specific mechanism by which stratified societies may have taken over most of the world,” says Marcus Feldman, an evolutionary biologist at Stanford University.


When resources were consistently scarce, egalitarian societies—which shared the deprivation equally throughout the population—remained more stable than stratified societies where the destabilizing effect of unequal sharing of scarce resources created more incentive to migrate in search of additional resources.

In environments where the availability of resources fluctuated from year to year, stratified societies were better able to survive the temporary shortages because the bulk of the deprivation was absorbed by the lower classes, leaving the ruling class—and the overall social structure—intact. That stability enabled them to expand more readily than egalitarian societies, which weren’t able to adapt to changing conditions as quickly.

Many possible causes for the development of socioeconomic inequality have been proposed by scientists, such as a need for hierarchical control over crop irrigation systems, or the compounding of small differences in individual wealth over time through inheritance.

“The fact that unequal societies today vastly outnumber egalitarian societies may not be due to the replacement of the ethic of equality by a more selfish ethic, as originally thought by many researchers,” says cultural evolution specialist Deborah Rogers, lead author of the study published in PLoS One.

“Instead, it appears that the stratified societies simply spread and took over, crowding out the egalitarian populations.

“This is not just an academic exercise,” says Rogers. “Inequalities in socioeconomic status are increasing sharply around the world. Understanding the causes and consequences of inequality and how to reduce it is one of the central challenges of our time.”

Funding was provided by the National Science Foundation, the Morrison Institute for Population and Resource Studies, Stanford University, and the National Institutes of Health.

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