Mary Towner: UC Davis Department of Anthropology

Cultural traits are distributed across human societies in a patterned way. Study of the mechanisms whereby
cultural traits persist and change over time is key to understanding human cultural diversity. For more than a
century, a central question has engaged anthropologists interested in the study of cultural trait variation—what
is the source of cultural variation? More precisely, are cultural traits transmitted primarily from ancestral to
descendant populations (through vertical transmission or inheritance) or between contemporary, typically
neighboring, populations (through horizontal transmission or diffusion), or do they emerge as independent
innovations? In addition, do traits in different domains, such as kinship and family, subsistence and
settlement, or material culture, show different transmission patterns? Addressing such questions has proven
to be methodologically challenging. Drawing on a research collaboration with Dr. Monique Borgerhoff Mulder
and Dr. Mark N. Grote, I will show how autologistic models can overcome some of the limitations of previous
approaches by placing the different transmission mechanisms on a more equal analytical footing. These
models can explicitly incorporate the structural links between societies, with geographical proximity being
used as a proxy for horizontal transmission, and linguistic classification being used as a proxy for vertical
transmission. I illustrate the method with an application to cross-cultural data from the Western North
American Indian database, a sample of 172 societies for which detailed ethnographic surveys were
conducted in the early 20th century. Alternative autologistic models are estimated through MCMC simulations
and then compared based on Akaike Information Criterion. The results suggest that the best models will
almost always incorporate both vertical and horizontal processes.