Household Task Delegation Among High-Fertility Forager-Horticulturalists of Lowland Bolivia

Human kin cooperation is universal, leading researchers to label humans as “cooperative breeders.” Despite widespread interest in human cooperation, there has been no systematic study of how household economic decision making occurs. We document age and sex profiles of task delegation by parents to children ages 4–18 among Bolivian forager-horticulturalists. We test for sex differences in the probability of delegation and examine whether tasks are more likely delegated as household labor demand increases. We also test whether food acquisition tasks are more likely delegated to higher producers.We find mixed support for the prediction that girls are more likely delegated domestic and alloparenting tasks than boys (np173 children). Both sexes are more likely delegated tasks during rice harvest months; number of coresident young children is also associated with greater probability of delegated allocare, although the effect retains significance for girls only. For both sexes, father absence is associated with greater probability of delegation, particularly for food acquisition tasks. Children delegated rice harvesting achieve 45% higher mean daily caloric returns from harvesting than children not delegated harvesting. Our results therefore suggest that delegation increases household economic efficiency. We find mixed support for the hypothesis that delegation prepares children for sex-specific adult roles

MHD flow and heat transfer in a rectangular duct

MHD Strömung und Wärmeübergang in einem Rechteckkanal Lediglich eine profunde Kenntnis des Wärmeübertragungsverhaltens laminarer und turbulenter magnetohydrodynamischer (MHD) Strömungen erlaubt eine adäquate Auslegung von Wärmeübertragern, zum Beispiel von Flüssigmetallblankets, oder eine Steuerung industrieller Verfahren durch den Einsatz von MHD Effekten. In diesem Bericht wird die experimentelle und numerische Untersuchung einer MHD-Strömung in einem Rechteckkanal mit elektrisch leitenden Wänden vorgestellt. Ein äußeres konstantes Magnetfeld B steht senkrecht auf der Kanalachse und ist ebenfalls senkrecht zum Wärmestrom , der von einem Strahlungsheizer erzeugt wird. Im Kanal werden sowohl integrale Größen wie der Druckverlust und die Nusselt-Zahl aber auch lokale Größen, zum Beispiel die Temperatur an der Fluid-Wand-Grenzfläche, die Geschwindigkeit und die lokale Temperatur ermittelt. Der untersuchte Parameterbereich umfaßt: Hartmann-Zahlen 0£ M£ 5000, Reynolds-Zahlen 0£ Re£ 1.3.105 und Peclet-Zahlen 0£ Pe£ 2900 . Der gemessene Druckverlust stimmt mit der analytischen Lösung für eine zweidimensionale MHD-Strömung in nahezu dem gesamten untersuchten Parameterbereich überein. Lediglich für Hartmann-Zahlen M£ 350 und Re³ 7.104 wird ein höherer Druckverlust ermittelt. Beim Überschreiten einer kritischen Reynoldszahl Recrit von Recrit=100.M entspricht der MHD-Druckverlust dem einer turbulenten hydrodynamischen Rohrströmung. Die Temperatur- und Geschwindigkeitsverteilung im Kanal, die mit einer kombinierten Temperatur- und Geschwindigkeitsmeßsonde (TEMPO) ermittelt wurde, stimmt mit den berechneten Werten für eine laminare MHD-Strömung überein. Die Nusselt-Zahl an der Wand ist bei MHD-Strömungen aufgrund der wandnahen Geschwindigkeitsüberhöhungen (den sogenannten Seitenwandjets), die sich an Wänden parallel zum Magnetfeld ausbilden und direkt dem Wärmestrom ausgesetzt ist, um ca. 30% größer als in einer hydrodynamischen Strömung. Bei großen M und sehr großen Re entspricht der Wärmeübergang der turbulenten MHD Strömung dem Wärmeübergang wie er auch in einer laminaren Strömung ermittelt wird. Der Grund dafür ist, daß die thermische Grenzschicht sich noch im Bereich der viskosen laminaren Grenzschicht befindet und somit leistet lediglich die molekulare Wärmeleitung einen Beitrag zur Wärmeübertragung. Bei bestimmten Parameterkonstellationen oder bei hinreichend langen Kanälen wächst die Grenzschicht in den Bereich der turbulenten Seitenwandschichten hinein. Durch den turbulenten Quertransport des Fluids wird der Wärmeübergang gesteigert. Die Wärmeübertragungsverbesserung kann um den Faktor 2 höher sein als bei einer laminaren MHD-Strömung

From the Womb to the Tomb: The Role of Transfers in Shaping the Evolved Human Life History

Humans are the longest living and slowest growing of all primates. Although most primates are social, humans are highly cooperative and social in ways that likely co-evolved with the slow human life history. In this paper we highlight the role of resource transfers and non-material assistance within and across generations in shaping low human mortality rates. The use of complex cooperative strategies to minimize risk is a necessary precursor for selecting further reductions in mortality rate in late adulthood. In conjunction with changes in the age-profile of production, the impacts of resource transfers and other forms of cooperation on reducing mortality likely played an important role in selection on post-reproductive lifespan throughout human evolution. Using medical data and ethnographic interviews, we explore several types of common risks experienced by Tsimane forager-horticulturalists, and quantify the types and targets of aid. Our results illustrate the importance of transfers in several key domains and suggest that the absence of transfers would greatly increase human mortality rates throughout the life course

Constraints on the salinity–oxygen isotope relationship in the central tropical Pacific Ocean

Uncertainties surround the relationship between salinity and the stable isotopic composition of seawater, largely due to a dearth of modern seawater isotope data. Here we report 191 new, paired measurements of salinity and seawater oxygen isotopes (δ¹⁸O_sw) taken from the central tropical Pacific in May 2012, from the surface to 4600 m depth. We observe significant correlations between δ¹⁸O_sw and salinity across the study region, with slopes ranging from 0.23 to 0.31‰/psu for the mixed layer, and 0.35–0.42‰/psu for waters between the mixed layer and 500 m depth. When considering δ¹⁸O_sw–salinity across averages of individual water masses in the region, slopes range from 0.21 to 0.40‰/psu, albeit with appreciable scatter. Surface salinity and δ¹⁸O_sw data corresponding to the North Equatorial Countercurrent are significantly higher than previously observed, which we attribute to a weak westerly current and dry conditions in the region during the May 2012 cruise. Subsurface (80–500 m) salinity values from 2012 are significantly lower than corresponding values from pre-existing regional data, highlighting a different latitudinal sampling distribution, while subsurface δ¹⁸O_sw is not significantly different. Thus, in May 2012, δ¹⁸O_sw in this region could not be used to distinguish between subsurface water masses of different salinities. Unlike other regions where the surface ‘freshwater endmember’ is close to the δ¹⁸O value of regional precipitation, the freshwater endmember implied by our dataset (− 10.38‰) is consistent with a strong evaporative influence. Paired δ¹⁸O–δD values of precipitation and surface seawaters have similar slopes (5.0, 5.1), and relatively low intercepts (1.4, 0.8) indicating isotopic variability in both reservoirs is also partly controlled by evaporation

Information flows from hippocampus to auditory cortex during replay of verbal working memory items

The maintenance of items in working memory (WM) relies on a widespread network of cortical areas and hippocampus where synchronization between electrophysiological recordings reflects functional coupling. We investigated the direction of information flow between auditory cortex and hippocampus while participants heard and then mentally replayed strings of letters in WM by activating their phonological loop. We recorded local field potentials from the hippocampus, reconstructed beamforming sources of scalp EEG, and - additionally in four participants - recorded from subdural cortical electrodes. When analyzing Granger causality, the information flow was from auditory cortex to hippocampus with a peak in the [4 8] Hz range while participants heard the letters. This flow was subsequently reversed during maintenance while participants maintained the letters in memory. The functional interaction between hippocampus and the cortex and the reversal of information flow provide a physiological basis for the encoding of memory items and their active replay during maintenance

The modulatory effect of self-paced and cued motor execution on subthalamic beta-bursts in Parkinson's disease: Evidence from deep brain recordings in humans

Deep brain stimulation (DBS) electrodes provide an unparalleled window to record and investigate neuronal activity right at the core of pathological brain circuits. In Parkinson's disease (PD), basal ganglia beta-oscillatory activity (13-35 Hz) seems to play an outstanding role. Conventional DBS, which globally suppresses beta-activity, does not meet the requirements of a targeted treatment approach given the intricate interplay of physiological and pathological effects of beta-frequencies. Here, we wanted to characterise the local field potential (LFP) in the subthalamic nucleus (STN) in terms of beta-burst prevalence, amplitude and length between movement and rest as well as during self-paced as compared to goal-directed motor control. Our electrophysiological recordings from externalised DBS-electrodes in nine patients with PD showed a marked decrease in beta-burst durations and prevalence during movement as compared to rest as well as shorter and less frequent beta-bursts during cued as compared to self-paced movements. These results underline the importance of beta-burst modulation in movement generation and are in line with the clinical observation that cued motor control is better preserved than self-paced movements. Furthermore, our findings motivate the use of adaptive DBS based on beta-bursts, which selectively trim longer beta-bursts, as it is more suitable and efficient over a range of motor behaviours than conventional DBS