Seasonality in a Mapuche native population

Human circadian rhythms are entrained by the environmental light-dark cycle. In this study we have recorded diurnal and seasonal variations in a Mapuche native community of Neuquen (Patagonia, Argentina), where environmental variables including photoperiod, temperature and rainfall vary substantially throughout the year and could be considered as potential zeitgebers of human rhythmicity. We have analyzed patterns of disease and medical visits throughout the year. They exhibited a clear peak after the winter, while paramedical visits appeared to be stable throughout this period. Moreover, daily sleep-wake cycles (assessed by analyzing 10-day sleep journals completed by primary school students) revealed a clear seasonal tendency, with a significant delay in wake-up time in winter with respect to summer (and, accordingly, an increase in alpha for the hot season). In most cases, waking up was triggered by luminosity or by the sound of a rooster. This is a clear demonstration of a seasonal component in human behavior, which also correlates with the seasonal migrations of this community between two locations. This study of native communities, without access to electricity and artificial light, offers a unique opportunity for understanding the role of natural environmental signals in circadian and seasonal entrainment.