"Long before it's in the papers"
January 27, 2015


More unequal societies spread faster, according to simulations

Sept. 28, 2011
Courtesy of Stanford University
and World Science staff

You might want to file this one un­der “life is­n’t fair.”

So­ci­eties with great­er in­e­qual­ity be­tween rich and poor tend nat­u­rally to ex­pand at the ex­pense of the oth­ers, ac­cord­ing to a new study based on sim­ula­t­ions. Re­search­ers say this may ex­plain why in­e­qual­ity is the norm to­day.

The study sug­gests that more un­equal so­ci­eties en­joy their suc­cess not de­spite the suf­fer­ing they cre­ate, but be­cause of it. They are prone to gen­er­at­ing mass­es of de­prived peo­ple who strike out in search of new land and op­por­tun­i­ties, en­er­get­ic­ally spread­ing their cul­ture but al­so its ten­den­cy to form class di­vi­sions. Mean­while, more equal, or egal­i­tar­ian, so­ci­eties tend to lan­guish.

That’s at least the view of re­search­ers at Stan­ford Uni­vers­ity in Cali­for­nia, who used a com­put­er sim­ula­t­ion to com­pare de­mo­graph­ic sta­bil­ity and rates of migra­t­ion for egal­i­tar­ian and un­equal, or strat­i­fied, so­ci­eties. 

“This is the first study to dem­on­strate a spe­cif­ic mech­an­ism by which strat­i­fied so­ci­eties may have tak­en over most of the world,” said Mar­cus Feld­man, an ev­o­lu­tion­ary bi­ol­o­gist at Stan­ford. He is a co-au­thor of a pa­per on the top­ic, pub­lished on­line this week in the re­search jour­nal PLoS One.

When re­sources were con­sist­ently scarce, egal­i­tar­ian so­ci­eties – which shared the de­priva­t­ion equally popula­t­ion-wide – re­mained more sta­ble than strat­i­fied so­ci­eties, Feld­man and col­leagues say. In strat­i­fied so­ci­eties, the desta­bilizing ef­fect of un­equal shar­ing gave those so­ci­eties more in­cen­tive to mi­grate.

In situa­t­ions where re­source avail­abil­ity fluc­tu­at­ed, strat­i­fied so­ci­eties were bet­ter able to sur­vive the tem­po­rary short­ages, the study sug­gests. This is­n’t be­cause their peo­ple were any hap­pi­er, but be­cause the low­er clas­ses took the brunt of the pain, 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.

Sci­en­tists have pro­posed many pos­si­ble causes for the de­vel­op­ment of so­ci­o­ec­onomic in­e­qual­ity, such as a need for hi­er­ar­chi­c 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,” said cul­tur­al ev­o­lu­tion spe­cial­ist Deb­o­rah Rog­ers, lead au­thor of the stu­dy. “In­stead, it ap­pears that the strat­i­fied so­ci­eties simply spread and took over, crowd­ing out the egal­i­tar­ian popula­t­ions.” The study is a prod­uct of her doc­tor­al the­sis proj­ect at Stan­ford. Feld­man was Rog­ers’ ad­vis­er.

“This is not just an ac­a­dem­ic ex­er­cise,” Rog­ers said. “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.”

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You might want to file this one under “life isn’t fair.” Societies with greater inequality between rich and poor tend naturally to expand at the expense of the others, according to a new study based on simulations. Researchers say this may explain why inequality is the norm today. The study suggests that more unequal societies enjoy their success not despite, but because of, the suffering that they create. They are prone to generating masses of deprived people who strike out in search of new land and opportunities, energetically spreading their culture but also its tendency to form class divisions. Meanwhile, more equal, or egalitarian, societies tend to languish in difficult times. That’s at least the view of Stanford University researchers, who used a computer simulation to compare demographic stability and rates of migration for both egalitarian and unequal, or stratified, societies. “This is the first study to demonstrate a specific mechanism by which stratified societies may have taken over most of the world,” said Marcus Feldman, an evolutionary biologist at Stanford. He is a co-author of a paper on the topic, published online this week in the research journal PLoS ONe. When resources were consistently scarce, egalitarian societies – which shared the deprivation equally population-wide – remained more stable than stratified societies, Feldman and colleagues say. In stratified societies, the destabilizing effect of unequal sharing gave those societies more incentive to migrate. In situations where resource availability fluctuated, stratified societies were better able to survive the temporary shortages, the study suggests. This isn’t because their people were any happier, but because the lower classes took the brunt of the deprivation, 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. Scientists have proposed many possible causes for the development of socioeconomic inequality, 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,” said cultural evolution specialist Deborah Rogers, lead author of the study. “Instead, it appears that the stratified societies simply spread and took over, crowding out the egalitarian populations.” The study is a product of her doctoral thesis project at Stanford. Feldman was Rogers’ adviser. “This is not just an academic exercise,” Rogers said. “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.”