Biological Rhythm Research 2004, Vol. •• No. ••. pp. ••–••

Seasonality in a Mapuche Native Population T.A. Bekinschtein1, A. Negro2, A. Goldín3, M.P. Fernández4, S. Rosenbaum5 and D.A. Golombek 1

Instituto de Investigaciones Neurológicas ‘Ramón Carrea’, Buenos Aires; School of Anthropology, University of Buenos Aires; 3School of Natural and Exact Sciences, University of Buenos Aires; 4Instituto Leloir, Buenos Aires; 5 Departamento de Ciencia y Tecnología, Universidad Nacional de Quilmes, Buenos Aires, Argentina 2

Abstract 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 Neuquén (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. Keywords: Sleep, seasonality, mapuche, natural entrainment.

Address correspondence to: Dr. Diego A. Golombek, Departamento de Ciencia y Tecnología, Universidad Nacional de Quilmes, R.S. Peña 1870, (1876) Bernal, Buenos Aires, Argentina. Tel. +54-11-4365-7100 ext 154; Fax +54-11-4365-7132; E-mail: [email protected] 0165-0424/04/000-000$22.00 © 2004 Taylor & Francis Ltd.

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Introduction Human biological timing can be understood in both cultural and biological contexts. Indeed, our brain encodes diverse mechanisms capable of coordinating temporal activities, and includes biological clocks that are able to measure diverse time frames, from seconds to days, and even years (see Dunlap et al., 2003). However, the concept of time duration and associated cycles is strongly associated with social and cultural roots, due to the imposed lifestyles of different societies (Adam, 1994, 1995; Levine, 1998). To some extent, it can be argued that we are prepared for a world that does not exist anymore (Moore-Ede, 1993). Our lives are not directly ruled by natural daylight or seasonal variables: the constant stimulation by potential synchronizers (artificial light, heating, work and school timetables) affects our biological clocks and also our subjective concept of time duration. The relative contribution of endogenous and exogenous factors to biological timing is thus difficult to assess. There are laboratory situations where all environmental variables can be controlled in order to understand how this temporal sense works in human beings (Khalsa et al., 2003; Golombek, 2003; Wever, 1979); however, this is a highly artificial situation removed from how the system works under natural conditions and how it evolved. The analysis of human communities where artificial stimuli are absent or greatly decreased constitutes an optimal situation for investigating biological timing and ‘time sense’. In this paper, we present our initial data about some seasonal variations in the native Mapuche population of Millaín Currical (in the province of Neuquén, Argentina). This population does not have electricity; therefore, it depends upon environmental variables and natural synchronizers.

Materials and Methods Geographical location and social characteristics The Mapuche community of Millaín Currical is located in the pre-Andean western region of the province of Neuquén, Argentina (37°55¢07≤S; 70°17¢45≤W). It is located about 40 km away from the nearest town, Loncopué (38°05¢S; 70°40¢W). The community is divided into two ‘parajes’ (sites): Huncal and Pichaihue. Each of these has a school and a sanitary post. The organization of the community is headed by a cacique (chief ), elected every two years by its members in a general assembly. There is also a cooperative that organizes general supplies for the community. The main way of living is the breeding of goats. There is also some commerce, involving their textiles and knitted goods. The land is not very fertile and this, together with the relative shortage of water, does not allow for a sustainable practice of agriculture. Analysis of environmental variables We used available data from the National Meteorological Service and also obtained our own data regarding average temperature, rainfall, wind velocity and luminance.

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Sleep journals Children from the ‘Paraje Huncal’ school, aged 10–14, filled out forms with their waking and sleeping time throughout 2-week periods. This was performed in June (Winter) and at the end of November (i.e., by the end of Spring). In these journals we also asked them to write any unusual feature of the day (i.e., sickness, special jobs, etc.) as well as the way of waking up (light, clock, rooster, etc.). Data were analyzed in order to determine the phase and variability of circadian sleep–wake cycles. Seasonal health patterns We had access to the databases of the Loncopué hospital; these enabled us to analyze the variation of medical and para-medical (i.e., dentistry, traumatology) consultations throughout the year. A total of 10 years (1992–2002) was analyzed and plotted.

Results Photoperiodic changes were significant throughout the year (Fig. 1a): the average value for the Summer scotophase was of 13.73 ± 0.80 h , and of 11.41 ± 0.04 h for the Winter (p > 0.0001, Student’s t test). Temperature and rainfall exhibited similar significant seasonal variations, as shown in Figure 1b: average rainfall for Summer and Winter months was, respectively, 12.06 and 61.16 mm, while temperature fluctuated from an average of 18.3°C (Summer) and 3.65°C (Winter). Medical consultations also showed a seasonal variation peaking in late Winterearly Spring (ANOVA: F = 2.26, p < 0.02); in contrast, paramedical visits did not change throughout the year (ANOVA: F = 1.34, p > 0.05) (Fig. 2). Thirty-four sleep journals were analyzed and indicated significant changes in wake-up time and, accordingly, in total hours awake (Fig. 3). It is interesting to consider that the seasonal changes (which correlate with the annual variation in photoperiod) in wake-up times were not extended to the timing of ‘getting up’. When asked for the timing of getting out of the bed, it was quite similar in both seasons (7.7 ± 0.7 h for the winter and 7.15 ± 0.5 h for the summer), since this time is probably defined by the daily obligations (i.e., school and farming).

Discussion Human circadian rhythms are entrained by environmental signals such as the daily photoperiod. However, electric light probably counteracts these subtle changes so that modern urban societies do not exhibit strong seasonal patterns. There have been a few studies where the photoperiod has been changed in laboratory conditions, and this has been found to induce neuroendocrine changes and also profoundly affect the sleep-wake cycle (Wehr, 1998). There are also studies of human circadian rhythms in extreme latitudes, such as the Arctic and the Antarctic regions (Yoneyama et al., 1999; Steel et al., 1995); however, in these cases the subjects had access to artificial

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Figure 1. Annual variation in environmental conditions. Upper panel: photoperiodic variation throughout the year, measured as total hours of daylight/day. Lower panel: changes in environmental temperature and average rainfall (measured in mm).

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Figure 2. Seasonal variations in total medical consultations of Millaín Currical inhabitants at the Loncopué hospital. A total of 10 years (1992–2002) were analyzed and plotted as average ± standard error for each month.

lighting and heating. It is clear that several behavioral, physiological and affective disorders show seasonal variations, which are undoubtedly normally masked by urban life. It is possible that these seasonal changes are exaggerated in human populations under natural entraining agents, and also that these signals are useful not only for adaptation to the environment but also for traditional and cultural activities. In this study we have found seasonal changes in behavior and medical visits in a native Mapuche population in Patagonia, which are in accordance with a strong seasonality in environmental variables such as photoperiod, temperature and rainfall. Indeed, in order to perform a complete correlation analysis, we would need sleep data

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Figure 3. Summer–winter differences in wake-up and sleep hours. ‘Clock time’ refers to rising/retiring times and ‘hours’ for time awake. *: p < 0.05, paired one-tail Student’s t test.

for longer periods of time. With 7–10 days of data (or the average value for that period) for each season we can only state that there is a correlation between sleep journals and environmental variables. Interviews with the students suggest that the most important variable for setting sleep–wake timing is the time of sunrise. The seasonal variation of visits to the hospital, peaking in August (i.e., by the end of Winter) might represent annual changes in the appearance of specific illnesses or, more simply, the fact that during June and July it is more difficult for the community to reach the Hospital in Loncopué, which is about 40 km away. However, the fact that paramedical visits do not show the same annual changes suggests that the first explanation is more plausible, and that the people are more prone to disease throughout the winter. We are currently analyzing what kind of diseases require the visits to the hospital. One of the most interesting features of this and other Mapuche communities is that every year they change their location between the ‘invernada’ (winter land) and ‘veranada’ (summer land). Every summer (usually starting in December), the same population migrates about 50 km west, leaving their winter lands and travelling with their families and animals to the other site, in order to have better pastures for the goats; families return to Huncal by April. This is another clear indication of a strong seasonal component in human social behavior, and we are currently researching the cultural and environmental driving forces for this seasonal migration.

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During their stay in the winter lands, children are required to attend primary school, which follows the regular Argentinean curriculum of education. In Millaín Currical, school is the only ‘socializing’ institution; indeed, the fact that the timing for ‘getting out of bed’ is similar in both seasons indicate that school might act as a social zeitgeber, complementing environmental information. School represents an excellent location for our studies, since we can not only gather data from the students but also include part of our scientific research in the educational curricula with the aid of their teachers. Indeed, we need data from the schoolchildren of Loncopué, to act as a control situation for students who enjoy electric light in their home. The school context needs some kind of definition of time use and time allocation, which is not necessarily imposed by the authorities. For example, personal communications from the schoolmaster indicate that the time of start of courses is determined by the time students arrive to the institution, which is consistently later during the winter (although, surprisingly, most students arrive at around the same time every day during a particular season). The study of time under anthropological perspectives is usually based upon the division between ‘traditional’ and ‘modern’ societies (e.g., Hill & Hurtado, 1993). One of the best known cases is the study by Evans-Pritchard, evidencing how the Nuer could structure time as a function of ecological cycles (Evans-Pritchard, 1940). However, most of the so-called ‘traditional’ societies now have a close interaction with ‘modern’ uses of time, including clocks and calendars, as well as a series of obligations such as attending to school or work. Nevertheless, the use of traditional time scales in ‘traditional’ societies has not been thoroughly studied. One of the few studies regarding circadian rhythmicity in a ‘traditional’ society is that of Siegmund and collaborators performed on the Trobriand islanders from the Tauwema village (Siegmund et al., 1998). 7-day studies with actometers showed that circadian behavior was regulated both by developmental factors (in particular related to the ultradian-circadian transition in young infants guided by parent-child interactions [e.g., Siegmund et al., 1994]) and the natural light-dark cycle. However, no seasonal changes were reported in the sleep patterns of Trobrianders. It is tempting to speculate that environmental signals relevant to community life might have been maintained in traditional stories and tales that have been passed on from generation to generation (Fernandez, 1988). Indeed, temporal patterns are fundamental to the economy of this Mapuche population, since seasonal farming is their main way of subsistence; in this sense, time has a definite ecological and economical relevance (Kümmerer, 1996; Reisch, 2001). In summary, this study represents the first analysis of a clear link between Mapuche lifestyle and the environment. When analyzing sleep–wake journals from Summer and Winter periods, a significant difference in wake-up time was found (being earlier in the Summer), which is in accordance with an expanded photophase for that season. Our subjects report that sunrise and natural light is one of the main factors for rising, supporting the notion that their habits are closely linked to Nature. In this sense, under the appropriate conditions, human might exhibit seasonal variations in their behavior (and presumably in their physiology) which might be considered as an adaptation to a changing environment.

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Acknowledgments Supported by Fundación Antorchas, Universidad de Buenos Aires and Universidad Nacional de Quilmes. The help from Gendarmería Nacional and schoolteachers from Huncal is gratefully acknowledged. We are grateful to the reviewers’ comments which helped us improve the manuscript.

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