Have you taken a direct-to-consumer ancestry test and had an unexpected or shocking result? Perhaps your ancestors were from a different part of the globe than you expected, or you found a long-lost relative. Our study of ancient DNA (aDNA) from individuals who lived at Paquimé (Chihuahua, Mexico) produced a similarly startling finding—a child with parents more closely related than first cousins. This discovery and other data from the site are shedding new light on the social structure of Paquimé.

Paquimé (also called Casas Grandes) is one of the largest and most important archaeological sites in Precontact Northwest Mexico and the Southwest United States (Northwest/Southwest). Paquimé dates to A.D. 1200-1450 and comprises a massive adobe complex (three or more stories tall in some places), with hundreds of rooms and features including ballcourts, roasting pits, cruciform- and serpent-shaped mounds, and an underground well at which ceremonies and rituals were held. The adobe complex closest to this well was named “The House of the Well” by Charles DiPeso, who excavated a significant portion of the site from 1959-1961. Along with housing thousands of exotic materials, the House of the Well also contained a 6–10-year-old male child buried beneath a large roof support post. This child was placed with turquoise and had evidence of a fatal blow to his skull, which led DiPeso to interpret the burial as a sacrifice. Our analysis of this child’s aDNA revealed that his parents were 2nd-degree relatives, meaning they shared 25-50% of their DNA (e.g. aunt/uncle-niece/nephew or half-siblings). The runs of homozygosity (RoH) levels we measured in the child are some of the highest in the ancient Americas (RoH are repetitive segments of an individual’s genome). We interpret the confluence of these lines of evidence—very high RoH, unique burial with luxurious goods and a sacrificial blow to the skull—as part of a ritual conducted by an elite family to aggrandize their social standing at Paquimé during the site’s apex.

Adobe architecture at Paquimé (credit: authors)

Our research is groundbreaking in many ways. The ancient genome published in this study is the first from Paquimé. Previous attempts to extract genome-wide data from Paquimé individuals have been unsuccessful, likely due to the region’s high heat, which severely damages aDNA. This work is a collaboration between Mexican and American archaeologists and geneticists affiliated with various institutions. Such interdisciplinary, cross-border research is especially important in an increasingly divided world. We hope this research demonstrates how people with different backgrounds and interests can build bridges across modern, arbitrary borders to learn about the people who lived before these borders existed. Moving forward, we will continue to examine the ancient genomes of the people who lived at Paquimé and in surrounding regions. Along with unexpected findings, such as with the child in this study, we will leverage aDNA to learn how people in the ancient Northwest/Southwest interacted with each other during the long human occupation of the region.

Read the associated research, out now in Antiquity: High levels of consanguinity in a child from Paquimé, Chihuahua, Mexico by Jakob Sedig et al.