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�鶹��Ѱ�����Boulder archaeologist Scott Ortman and colleagues around the world explore relationships between housing size and inequality in PNAS Special Feature

If the archaeological record has been correctly interpreted, stone alignments in Tanzania’s Olduvai Gorge are remnants of shelters built 1.7 million years ago by Homo habilis, an extinct species representing one of the earliest branches of humanity’s family tree.

Archaeological evidence that is unambiguously housing dates to more than 20,000 years ago—a time when large swaths of North America, Europe and Asia were covered in ice and humans had only recently begun living in settlements.

Between that time and the dawn of industrialization, the archaeological record is rich not only with evidence of settled life represented by housing, but also with evidence of inequality.

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�鶹��Ѱ�����Boulder archaeologist Scott Ortman partnered with colleagues Amy Bogaard of the University of Oxford and Timothy Kohler of the University of Florida on a PNAS Special Feature focused on housing size in the archaeological record and inequality.

In a , scholars from around the world draw from a groundbreaking archaeological database that collects more than 55,000 housing floor area measurements from sites spanning the globe—data that support research demonstrating various correlations between housing size and inequality.

“Archaeologists have been interested in the study of inequality for a long time,” explains Scott Ortman, a �鶹��Ѱ����� associate professor of anthropology who partnered with colleagues Amy Bogaard of the University of Oxford and Timothy Kohler of Washington State University to bring together the PNAS Special Feature. (Special Features in PNAS are curated collections of articles that delve into important topics.)

“For a long time, studies have focused on the emergence of inequality in the past, and while some of the papers in the special feature address those issues, others also consider the dynamics of inequality in more general terms.”

Kohler notes that "we use this information to identify the fundamental drivers of economic inequality using a different way of thinking about the archaeological record—more thinking about it as a compendium of human experience. It’s a new approach to doing archaeology.”

Patterns of inequality

Ortman, Bogaard and Kohler also are co-principal investigators on the Project funded by the National Science Foundation and housed in the �鶹��Ѱ�����Boulder in the Institute of Behavioral Science to create the database of housing floor area measurements from sites around the world.

Scholars then examined patterns of inequality shown in the data and studied them in the context of other measures of economic productivity, social stability and conflict to illuminate basic social consequences of inequality in human society, Ortman explains.

“What we did was we crowdsourced, in a sense,” Ortman says. “We put out a request for information from archaeologists working around the world, who knew about the archaeological record of housing in different parts of world and got them together to design a database to capture what was available from ancient houses in societies all over world.”

Undergraduate and graduate research assistants also helped create the database, which contains 55,000 housing units and counting from sites as renowned as Pompeii and Herculaneum, to sites across North and South America, Asia, Europe and Africa. “By no stretch of the imagination is it all of the data that archaeologists have ever collected, but we really did make an effort to sample the world and pull together most of the readily available information from excavations, from remote sensing, from LiDAR,” Ortman says.

The housing represented in the data spans non-industrial society from about 12,000 years ago to the recent past, generally ending with industrialization. The collected data then served as a foundation for 10 papers in the PNAS Special Feature, which focus on the archaeology of inequality as evidenced in housing.

Housing similarities

In their introduction to the Special Feature, Ortman, Kohler and Bogaard note that “economic inequality, especially as it relates to inclusive and sustainable social development, represents a primary global challenge of our time and a key research topic for archaeology.

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In the PNAS Special Feature published Monday, researchers from around the world describe evidence of inequality found in archaeological data of housing size. (Cover image: Johnny Miller/Unequal Scenes)

“It is also deeply linked to two other significant challenges. The first is climate change. This threatens to widen economic gaps within and between nations, and some evidence from prehistory associates high levels of inequality with lack of resilience to climatic perturbations. The second is stability of governance. Clear and robust evidence from two dozen democracies over the last 25 years that links high economic inequality to political polarization, distrust of institutions and weakening democratic norms. Clearly, if maintenance of democratic systems is important to us, we must care about the degree of wealth inequality in society.”

Archaeological evidence demonstrates a long prehistory of inequality in income and wealth, Ortman and his colleagues note, and allows researchers to study the fundamental drivers of those inequalities. The research in the Special Feature takes advantage of the fact “that residences dating to the same chronological period, and from the same settlements or regions, will be subject to very similar climatic, environmental, technological and cultural constraints and opportunities.”

Several papers in the Special Feature address the relationship between economic growth and inequality, Ortman says. “They’re thinking about not just the typical size of houses in a society, but the rates of change in the sizes of houses from one time step to the next.

“One thing we’ve also done (with the database) is arrange houses from many parts of the world in regional chronological sequences—how the real estate sector of past societies changed over time.”

The papers in the Special Feature focus on topics including the effects of land use and war on housing disparities and the relationship between housing disparities and how long housing sites are occupied. A study that Ortman led and conducted with colleagues from around the world found that comparisons of archaeological and contemporary real estate data show that in preindustrial societies, variation in residential building area is proportional to income inequality and provides a conservative estimator for wealth inequality.

“Our research shows that high wealth inequality could become entrenched where ecological and political conditions permitted,” Bogaard says. “The emergence of high wealth inequality wasn’t an inevitable result of farming. It also wasn’t a simple function of either environmental or institutional conditions. It emerged where land became a scarce resource that could be monopolized. At the same time, our study reveals how some societies avoided the extremes of inequality through their governance practices.”

The researchers argue that “the archaeological record also shows that the most reliable way to promote equitable economic development is through policies and institutions that reduce the covariance of current household productivity with productivity growth.”

GINI Project data, as well as the analysis program developed for them, will be available open access via the��.

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