Changes in mobility have long been considered a critical factor affecting social and economic change during transitions from hunting and gathering to food production. Archaeologists have relied on a wide range of indirect indicators of sedentism and the intensity of site occupation such as site size and structural complexity. One of the key problems has been how to ascertain more precisely how change in mobility combined with other factors of economic and social intensification. More than 40 years ago, Tchernov (Bar-Yosef and Tchernov 1966) first proposed the idea that remains of commensal species that today coexist with humans in settlement environments could be used to detect early sedentism in the archaeological record. Subsequent studies of the earliest occurrence of commensal house mice (Mus musculus domesticus ) in sites of complex Natufian hunter-gatherers of southwest Asia established a link between pronounced levels of commensalism and what is generally believed to have been one of the first sedentary cultures in the world. The commensalism model related increasing populations of commensal species and decreasing biological diversity to changes in the intensity of human site occupation. It was expressly developed to test assumptions about decreasing mobility among Natufian hunter-gatherers and their role in the subsequent domestication of plants and animals and emergence of agricultural villages. The validity of the model was later questioned, however, due to the lack of empirical knowledge on commensalism in a wide range of settlement environments including sedentary and more mobile ones. This research was designed to test Tchernov's commensalism hypothesis through a study of seasonally occupied settlements of Maasai pastoralists in East Africa. Methods from ecology, ethnography, and archaeology were used to document the impact of Maasai settlements on associated communities of small rodents and shrews (micromammals), to measure the intensity of human occupation in settlements, and to relate settlement intensity to micromammalian communities. Taphonomic approaches were also used to evaluate the potential for accumulation and preservation of evidence on commensalism in the substrate of the settlements. The results of the study showed that, in contrast to what we might expect in highly sedentary settings, Maasai settlements increased rather than decreased the biological diversity of local micromammalian communities. Along a gradient of decreasing settlement mobility, but continued seasonal use of settlements, there was no manifest increase in the population of any single species that would amount to pronounced commensalism. This supports the commensalism/sedentism linkage but also suggests more broadly that it should be possible to demarcate distinct contexts of commensalism and related levels of biological diversity in relation to varying intensities of site occupation. These results call for greater investment in systematic fine-recovery and study of variability of micromammalian assemblages at archaeological excavations
