Because of culture, humans are often considered to be divorced from the environment and not under the same ecological forcing as other species. However, in a new paper published in Proceedings of the National Academy of Sciences (PNAS) scientists from the University of Helsinki, Faculty of Science, show that key environmental parameters, namely climate-related primary productivity, biodiversity, and pathogen stress, have strong influence on the global pattern of population densities of ethnographically documented hunter-gatherers.