Suppose current interpretations of the archaeological record are accurate. In that case, a series of stone alignments found in Tanzania’s Olduvai Gorge may represent the remains of shelters constructed 1.7 million years ago by Homo habilis, an extinct hominin species considered one of the earliest branches in the human evolutionary lineage. If correctly identified as shelters, these rudimentary structures would considerably push back the timeline for early human habitation.

However, the most precise and unambiguous evidence for housing—structures indisputably built and lived in by humans—dates to just over 20,000 years ago. This period coincides with the last Ice Age, when glaciers blanketed large portions of North America, Europe, and Asia. It also marks a point in human history when communities had only recently formed settled societies. From this time forward, particularly before the onset of industrialisation, the archaeological record becomes increasingly rich. Not only does it reveal the prevalence of housing as a hallmark of settled life, but it also uncovers significant clues regarding the emergence and evolution of social inequality.

A newly published PNAS Special Feature brings together an international team of scholars collaborating to analyse these patterns through a pioneering archaeological initiative. Central to their work is an extensive database comprising over 55,000 housing floor area measurements drawn from archaeological sites worldwide. This vast dataset underpins a series of studies demonstrating compelling correlations between the size of residential structures and levels of economic inequality in various historical contexts.

Scott Ortman, an associate professor of anthropology at the University of Colorado Boulder, worked alongside Amy Bogaard of the University of Oxford and Timothy Kohler of the University of Florida to coordinate this special collection. According to Ortman, archaeologists have long been interested in understanding inequality, often focusing on how and when it emerged. However, the current body of research goes further, seeking to understand the broader dynamics that have shaped economic disparities across time and space. The team has adopted a novel perspective, treating the archaeological record as a sequence of ancient artefacts and a comprehensive repository of human experience. This shift in approach represents an exciting development in archaeological methodology.

The core of this work stems from the Global Dynamics of Inequality (GINI) Project, supported by the National Science Foundation and headquartered at CU Boulder’s Center for Collaborative Synthesis in Archaeology. Ortman, Bogaard, and Kohler, all co-principal investigators, led a global effort to compile housing data from non-industrial societies dating from approximately 12,000 years ago to the advent of industrialisation. By reaching out to archaeologists with regional expertise, the team effectively “crowdsourced” the data collection process, assembling a wide-ranging database that draws on both published excavation records and cutting-edge remote sensing technologies such as LiDAR. Sites represented include the famously preserved cities of Pompeii and Herculaneum, alongside less celebrated but equally informative locations across the Americas, Europe, Africa, and Asia.

Although the dataset does not yet encompass every instance of residential architecture uncovered by archaeology, it represents a highly ambitious and impressively comprehensive sampling of what is currently accessible. Undergraduate and graduate students were crucial in organising and entering the data. With over 55,000 individual housing units catalogued, the database has become a foundational tool for analysing inequality in pre-industrial contexts. Ten papers within the PNAS Special Feature use this information trove to explore how housing size variations reflect broader social and economic trends, particularly the distribution of wealth and power.

In their introductory essay, Ortman, Kohler, and Bogaard underscore the pressing relevance of their research. They frame economic inequality as one of the foremost global challenges of the twenty-first century, closely tied to other critical issues such as climate change and the stability of democratic governance. Prehistoric data, they argue, suggest that societies with pronounced inequalities were often less resilient to environmental shocks. Furthermore, recent evidence from modern democracies indicates that economic disparity undermines political trust and weakens institutional legitimacy. These insights highlight the vital role of archaeology in illuminating not only the distant past but also the foundational mechanisms shaping the present and future of human societies.

Notably, the Special Feature explores how residential data from the same periods and regions—subject to consistent environmental, technological, and cultural conditions—offer valuable comparisons. Some papers examine how wealth inequality evolved with economic growth, focusing on how average house sizes changed over time and what these shifts reveal about access to resources. Others investigate the impact of land use practices, warfare, and duration of site occupation on housing disparities. One key study, led by Ortman and involving an international team, draws a direct connection between variability in house sizes in ancient societies and measures of income inequality used in contemporary settings. Their findings suggest that residential floor area is a conservative but effective proxy for estimating historical wealth disparities.

Bogaard emphasises that wealth inequality did not inevitably follow the advent of agriculture. Instead, high levels of inequality only became entrenched in specific ecological and political contexts—particularly where land could be monopolised. Conversely, some societies managed to maintain relatively egalitarian structures through governance systems designed to curb the accumulation of excess wealth and to promote equitable access to resources. The archaeological record, she asserts, offers powerful lessons for modern societies. It indicates that equitable economic development is best supported by institutions and policies that reduce the reinforcement of inequality through successive generations. In short, understanding the roots of inequality through the lens of ancient housing can help us better address the challenges we face today.

More information: Scott Ortman et al, Economic inequality is fueled by population scale, land-limited production, and settlement hierarchies across the archaeological record, Proceedings of the National Academy of Sciences. DOI: 10.1073/pnas.2400691122

Journal information: Proceedings of the National Academy of Sciences Provided by University of Colorado at Boulder