In ancient Rome, the wealthy patricians ran the empire. The second-class plebeians worked the farms, baked the bread and built the walls. The rest of the workforce—a full third of the Roman population—were slaves.

Human history is, sadly, entwined with inequality. Most early civilizations, the Sumerians, Egyptians and Harappans among them, had social classes—strata of inequity that left some better positioned than others. Yet it has long been assumed that prior to the Athenian and Roman empires,—which arose nearly 2,500 and more than 2,000 years ago, respectively—human social structure was relatively straightforward: you had those who were in power and those who were not. A study published Thursday in Science suggests it was not that simple. As far back as 4,000 years ago, at the beginning of the Bronze Age and long before Julius Caesar presided over the Forum, human families of varying status levels had quite intimate relationships. Elites lived together with those of lower social classes and women who migrated in from outside communities. It appears early human societies operated in a complex, class-based system that propagated through generations.

By analyzing the DNA of more than 100 ancient skeletons from a burial site near Augsburg, Germany, the researchers determined the sex and relatedness of individuals buried together on single farmsteads. They were members of Central European farming communities that spanned from the late Neolithic period through the Bronze Age—or from around 2800 B.C. through 1300 B.C. Related individuals, the study’s authors found, were laid to rest with goods and belongings that appeared to be passed down through generations. The unrelated people in the household were buried with nothing, suggesting they were a lower class of “family members,” who were not given the ceremonial treatment.

“We don’t know if the low-status individuals in Augsburg were slaves, menial staff or something else,” comments Philipp Stockhammer of the Ludwig Maximilian University of Munich, who was a co-author of the new study. “But we can see that in every household, individuals of very different status were living together.”

By radio dating the teeth samples and comparing them with regional geographical radioactivity profiles, Stockhammer and his collaborators also determined where each person grew up. Traces of radioactive elements called isotopes are all around us, including in our food and water. From childhood, these elements are incorporated into our bones and can be used to determine where someone was raised. The results show that in nearly all of the households studied, there were females who hailed from elsewhere.

Whereas the remains suggest that farmsteads were passed through many generations of males—up to five in some cases—females only persisted in a community for one generation. This observation means a system of patrilocality was followed: men stayed in their place of upbringing, while women moved in with their husband’s family. Patrilocal cultures had previously existed, including far back in the Paleolithic, but the findings support the idea that the practice became more common as the organization of societies developed.

Stockhammer points out that social structure has long been a major topic in archeology and that countless studies have explored the communal interactions of ancient societies. Yet he feels the new study illuminates the transition of societal organization as we moved, from the late Stone Age to the Bronze Age, toward individual families living with those of a subservient class and women from other communities. “We added a new aspect to the current state of the art: the integration of genetic, isotopic and archaeological data, which helped us understand the complexity of past social structures,” Stockhammer says. Though he is resolute that his findings cannot directly be correlated with other ancient societies, he does draw a comparison with classical Greece’s oikos family structure and Rome’s familia, in which slaves and those of lower status were part of the family.

University of Michigan archeologist Alicia Ventresca Miller, who was not involved in the paper, shares Stockhammer’s enthusiasm and feels this new work reveals a lot about early human inheritance of goods and property. “As far as I can tell, there are no other studies that have such large sample sizes and multiple analyses to come to these conclusions, especially for prehistoric groups,” she says. “Their finding that wealth was inherited, rather than achieved, has real impacts for research on inequality and will likely change our understanding of ancient Europe. The results give us insight into the complexity of ancient lifeways.”

Krishna Veeramah, a population geneticist in the department of ecology and evolution at Stony Brook University, who was also not involved in the study, thinks the new multidisciplinary research approach may serve as a model for future work, especially as characterizing ancient DNA becomes more affordable and widespread.

For his part, Stockhammer believes marrying outside one’s community encouraged the cultural exchange of information, which ultimately led to the formation of new civilizations. Increasing social interactions with other communities allowed for a more efficient transfer of skills and goods to a wider population. “I am sure the fact that a large number of adult women from outside the society entered the society had an important effect—that new knowledge and technologies came with them,” he says.

Anthropologists and scientists from other fields refer to a concept called ratcheting, in which cultural information is not just shared and learned but also modified and improved. If ancient humans mingled with outside communities, countless kernels of know-how would have been borrowed and altered for both good and bad (more effective tools; more lethal weapons and warfare).

Individuals marrying outside of their community may have also made sense from the standpoint of genetic fitness and allowed local societies to thrive. Doing so would have prevented the genetic abnormalities that come from inbreeding and perhaps, in the long term, improved collective community survival.

Stockhammer already has plans to expand his work to areas beyond just Augsburg in hopes of assembling a more comprehensive view of Bronze Age social structure. He aims to develop a picture of how we lived, interbred and formed cultural groups—and how and when class division, or structured inequality, arose in human society.