Downloaded fromwhen approaching the HOMO or LUMO resonance of the molecular wire (28). The increased conductance at higher bias voltages then compensates for the molecular wire length increase in Fig. 4B (a factor of 40 is not sufficient for the achieved current increase). Thus, such a setup allows the determination of the small conductance (8.6 × 10 -13 S) of a single and the same molecular wire with 20 nm length (the conductance at small bias voltages cannot be measured over such a large distance, due to the extremely low current-below the detection limit-passing through the polymer in this case). In this regard, it would be interesting to prepare and study conjugated polymers with smaller HOMO-LUMO gaps. Such molecular wires should exhibit higher conductances and allow charge transport to be determined over even larger distances. Hominin footprints offer evidence about gait and foot shape, but their scarcity, combined with an inadequate hominin fossil record, hampers research on the evolution of the human gait. Here, we report hominin footprints in two sedimentary layers dated at 1.51 to 1.53 million years ago (Ma) at Ileret, Kenya, providing the oldest evidence of an essentially modern human-like foot anatomy, with a relatively adducted hallux, medial longitudinal arch, and medial weight transfer before push-off. The size of the Ileret footprints is consistent with stature and body mass estimates for Homo ergaster/erectus, and these prints are also morphologically distinct from the 3.75-millionyear-old footprints at Laetoli, Tanzania. The Ileret prints show that by 1.5 Ma, hominins had evolved an essentially modern human foot function and style of bipedal locomotion. Bipedalism is a key human adaptation that appears in the fossil record by 6 million years ago (Ma) (1). Considerable debate continues over when and in what context a modern human-like form of bipedalism evolved, because of a fragmentary record and disagreements over the functional interpretations of existing fossils and footprints (2-7). Modern human footprints reflect the specialized anatomy and function of the human foot, which is characterized by a fully adducted hallux, a large and robust calcaneus and tarsal region, a pronounced medial longitudinal arch, and short toes (2). Footprints reflect the pressure distribution as the foot makes contact with the substrate, but also the sediment's geomechanical properties (8). During normal walking, the weight-bearing foot undergoes a highly stereotypical movement and pressure distribution pattern in which the heel contacts the ground first, making a relatively deep impression on the substrate. This is followed by contact with the lateral side of the foot and metatarsal heads, after which weight transfers to the ball of the foot with peak pressure under the medial metatarsal heads, and finally ending with toe-off pressure under the hallux (9, 10). As a consequence, the deepest part of a footprint often occurs beneath the first and second metatarsal heads, that along with a deep hallucal impression cor...
Grasslands are one of the world's most extensive terrestrial biomes and are central to the survival of herders, their livestock and diverse communities of large wild mammals. In Africa, tropical soils are predominantly nutrient-limited but productive grassy patches in wooded grassland savannah ecosystems grow on fertile soils created by geologic and edaphic factors, megafauna, fire and termites. Mobile pastoralists also create soil-fertility hotspots by penning their herds at night, which concentrates excrement-and thus nutrients-from grazing of the surrounding savannahs. Historical anthropogenic hotspots produce high-quality forage, attract wildlife and increase spatial heterogeneity in African savannahs. Archaeological research suggests this effect extends back at least 1,000 years but little is known about nutrient persistence at millennial scales. Here we use chemical, isotopic and sedimentary analyses to show high nutrient and N enrichment in on-site degraded dung deposits relative to off-site soils at five Pastoral Neolithic sites (radiocarbon dated to between 3,700 and 1,550 calibrated years before present (cal. BP)). This study demonstrates the longevity of nutrient hotspots and the long-term legacy of ancient herders, whose settlements enriched and diversified African savannah landscapes over three millennia.
Monumental architecture is a prime indicator of social complexity, because it requires many people to build a conspicuous structure commemorating shared beliefs. Examining monumentality in different environmental and economic settings can reveal diverse reasons for people to form larger social units and express unity through architectural display. In multiple areas of Africa, monumentality developed as mobile herders created large cemeteries and practiced other forms of commemoration. The motives for such behavior in sparsely populated, unpredictable landscapes may differ from well-studied cases of monumentality in predictable environments with sedentary populations. Here we report excavations and ground-penetrating radar surveys at the earliest and most massive monumental site in eastern Africa. Lothagam North Pillar Site was a communal cemetery near Lake Turkana (northwest Kenya) constructed 5,000 years ago by eastern Africa's earliest pastoralists. Inside a platform ringed by boulders, a 119.5-m mortuary cavity accommodated an estimated minimum of 580 individuals. People of diverse ages and both sexes were buried, and ornaments accompanied most individuals. There is no evidence for social stratification. The uncertainties of living on a "moving frontier" of early herding-exacerbated by dramatic environmental shifts-may have spurred people to strengthen social networks that could provide information and assistance. Lothagam North Pillar Site would have served as both an arena for interaction and a tangible reminder of shared identity.
Throughout the Holocene, Lake Turkana has been subject to drastic changes in lake levels and the subsistence strategies people employ to survive in this hot and arid region. In this paper, we reconstruct the position of the lake during the Holocene within a paleoclimatic context. Atmospheric forcing mechanisms are discussed in order to contextualize the broader landscape changes occurring in eastern Africa over the last 12,000 years. The Holocene is divided into five primary phases according to changes in the strand-plain evolution, paleoclimate, and human subsistence strategies practiced within the basin. Early Holocene fishing settlements occurred adjacent to high and relatively stable lake levels. A period of high-magnitude oscillations in lake levels Afr Archaeol Rev (2015) ensued after 9,000 years BP and human settlements appear to have been located close to the margins of the lake. Aridification and a final regression in lake levels ensued after 5,000 years BP and human communities were generalized pastoralists-fishers-foragers. During the Late Holocene, lake levels may have dropped below their present position and subsistence strategies appear to have been flexible and occasionally specialized on animal pastoralism. Modern missionary and government outposts have encouraged the construction of permanent settlements in the region, which are heavily dependent on outside resources for their survival. Changes in the physical and cultural environments of the Lake Turkana region have been closely correlated, and understanding the relationship between the two variables remains a vital component of archaeological research.Résumé Tout l'Holocène, le lac Turkana a été soumis à des changements drastiques dans l'altitude des lacs et les stratégies de subsistance des gens utilisent pour survivre dans cette région chaude et aride. Dans cet article, nous reconstruisons la position du lac au cours de l'Holocène dans un contexte paléoclimatique. Mécanismes de forçage atmosphériques sont discutées afin de contextualiser les changements de paysage plus larges qui se produisent en Afrique orientale au cours des 12.000 dernières années. L'Holocène est divisé en cinq phases principales en fonction des changements dans l'évolution altitude du lac, paléoclimats et les stratégies de subsistance humains pratiqués dans le bassin. Premiers établissements de pêche de l'Holocène ont eu lieu à proximité d'altitude d'eau élevés et relativement stables. Une période d'oscillations de grande amplitude dans l'altitude du lac s'ensuit après 9000 années BP et les établissements humains semblent avoir été situé à proximité des marges sur le lac. Aridification et une régression finale du altitude des lacs s'ensuit après 5000 années BP et les communautés humaines sont généralisées éleveurs-pêcheurs-cueilleurs. Au cours de l'Holocène tardif, les altitudes des lacs pourraient avoir chuté en dessous de leur position actuelle et les stratégies de subsistance semblent avoir fait preuve de souplesse et de temps en temps spécialisé sur le pas...
The Holocene was time of dramatic climate change in East Africa, shifting from wetter climate in the Early-Mid Holocene (ϳ10-5 ka) to drier climates in the Late Holocene, followed by a slight reversal at Ͻ1 ka. The Holocene was a time of cultural change from huntergatherer and fishing to pastoralism. Recent excavations along the eastern shores of Lake Turkana, Kenya (4°N) provide new archaeological materials, a high-resolution stratigraphic and paleoenvironmental data set, OSL dates, and cultural records in the context of documented environmental change (falling lake levels). Archaeological site FwJj25 (4.20 Ϯ 0.28 ka), on the northeastern margin of Lake Turkana, provides one of the earliest records of pastoralism in the region. The palimpsest record of FwJj5 (0.90 Ϯ 0.06 ka) was in a small valley containing a groundwater seep located 5 km from the lake. FwJj5 reflects occupation by people who may have covered great distances in accessing resources, but were likely drawn to an environmental refugia of freshwater springs during times of regional aridity.
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