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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.anbehav.2010.04.002 Byline: Amy L. Schreier (a), Matt Grove (b)(c) Abstract: Random walks have long been used to characterize animal movement patterns; recently, this practice has received renewed impetus via the application of Levy walk models. Whilst such models have produced encouraging results, the methods applied have been inconsistent and often problematic; furthermore, primates remain under-represented in such studies. This paper addresses both of these problems via the explanation of a novel and robust analytical method as applied to an extensive primate data set. In a study of a band of hamadryas baboons at the Filoha outpost of Awash National Park, Ethiopia from March 2005 to February 2006, the baboons' location was mapped every 15min during all-day follows using a handheld GPS unit, yielding over 3000 step lengths and waiting times documented across 105 complete follows. Both power law and exponential models were fitted to the step length and waiting time data via maximum likelihood procedures within a model selection paradigm facilitated by the use of an information criterion to distinguish between models. Results show that the step lengths were exponentially distributed, and thus consistent with a random distribution of resources in space. Waiting times, however, were power law distributed, and thus consistent with a power law distribution of patch sizes. We evaluate these results within a discussion of the extent to which random search algorithms are applicable to animals with extensive knowledge of their habitats. Author Affiliation: (a) Department of Evolutionary Anthropology, Duke University, U.S.A. (b) Institute of Cognitive and Evolutionary Anthropology, University of Oxford, U.K. (c) Brasenose College, Radcliffe Square, Oxford, U.K. Article History: Received 2 February 2010; Revised 22 February 2010; Accepted 18 March 2010 Article Note: (miscellaneous) MS. number: A10-00072R

Central Africa is a key region for examining patterns of hunter-gatherer inhabitation and engagement with ecological diversity and environmental change. In contrast to adjacent regions, however, the archaeological record of prehistoric hunter-gatherer populations in Central Africa is underrepresented in studies of recent human evolution. This limited engagement with Central African archaeological records in part stems from the complexities of identifying, excavating, and dating hunter-gatherer sites in what are today often heavily forested environments, a focus on named stone tool industries from undated sites to structure the record, and highly limited means to associate dated hunter-gatherer occupations with proxy records of environmental conditions. Here, we present a novel synthesis of prehistoric hunter-gatherer stone tool assemblages from dated Central African sites and use climate model datasets to illuminate the environmental and ecological landscapes in which they were deployed. Our results suggest a significant ecological shift occurred from 14,000 years ago onwards, associated with a greater engagement with broadleaf forests. We examine the extent to which a range of geographic and paleoclimatic drivers can explain patterns of gross assemblage composition and the appearance of individual lithic technologies highlighting the significant role of changes in altitude, precipitation, seasonality, and ecology. Notably, considerable continuity can be observed between the habitat ranges of contemporary hunter-gatherer populations in Central Africa and prehistoric occupations that significantly precede the appearance of farming lifeways in the region. • Synthetic review of Late Pleistocene and Holocene lithic assemblages in Central Africa. • Environmental contextualization of lithic assemblages over time. • Shift of environmental context occupied by Central African hunter-gatherers identified in the Pleistocene-Holocene transition. • Quantitative assessment of drivers of similarity in assemblage composition over time. • Altitude, site type, ecology and precipitation seasonality identified as significant drivers of similarity in assemblage composition. [ABSTRACT FROM AUTHOR]

The origin and initial dispersal of Homo sapiens out of East Africa and into the Levant remains a major research focus in evolutionary anthropology. There is little doubt that climatic changes played a role in facilitating this dispersal, but the specific dynamics remain poorly understood. This contribution surveys the fossil and genetic evidence for the origin and dispersal of modern humans, and situates this evidence within the context of biological theories of plasticity and dispersal. It is shown that certain climatic and environmental conditions are expected to lead to the evolution of plastic strategies, and that such strategies are characteristic of successfully dispersing species. A model is formulated that allows for the identification of features in climatic records that are conducive to the evolution of plasticity, and thus to the development of dispersal capabilities. Using as an example a palaeoclimatic record from Lake Tana, Ethiopia, the model is used to pinpoint the chronology of likely periods of dispersal from East Africa. Results indicate the presence of a dispersal phase c.97–105 ka, a date that fits well with the initial modern human colonisation of the Levant shortly after 100 ka. Implications of recent genetic chronologies for the origin of non-African modern humans and the archaeological evidence for possible routes out of Africa are discussed in this context. [ABSTRACT FROM AUTHOR]

Abstract: Many explanations have been proposed for the evolution of our anomalously large brains, including social, ecological, and epiphenomenal hypotheses. Recently, an additional hypothesis has emerged, suggesting that advanced cognition and, by inference, increases in brain size, have been driven over evolutionary time by the need to deal with environmental complexity. The essential logic is that orbital variables have affected the quantity of solar energy reaching the earth, thus creating climatic changes that posed adaptive challenges to ancestral humans. Larger-brained humans were better equipped to deal with such changes, and proliferated accordingly, leading to the observed trajectory of increasing brain size. Though cross-citation remains rare, researchers from areas as apparently disparate as philosophy and botany are ultimately reaching similar conclusions. In order to test the validity of hypotheses linking encephalisation to climatic variability in the human lineage, the endocranial volumes of 180 fossil human skulls spanning the last 3.2million years were collated from the literature and regressed upon a series of palaeoclimatic variables, including the amplitudes of the orbitally induced eccentricity, obliquity, and precession cycles. Multiple regression analyses demonstrate that the minimum amplitude of the eccentricity cycle explains 43% of the variance in endocranial capacity, with two further climatic variables accounting for a further 16%. These results are discussed in relation to the increasing weight of evidence that suggests that climatic instability may have played a significant part in the evolution of advanced cognition in both humans and other animals. [Copyright &y& Elsevier]

Over the past 25 years research concerning the effects of climatic fluctuations on past human societies has shifted focus considerably, with most recent hypotheses emphasizing shorter-term variability over longer-term change. Definitions of change and variability, however, remain subjective and vary considerably between researchers. It is suggested that white noise, due to its inherent unpredictability, provides a theoretically robust model of variability that accords with perceptions of variability conveyed by the existing literature. The use of white noise as a model for variability enables the development of an algorithm that objectively decomposes an empirical climatic signal into change and variability components. The algorithm, which combines singular spectrum analysis and Fourier methods, is validated via an extensive series of simulations and applied via two empirical case studies. It is shown that the algorithm has the potential to produce genuine advances by isolating features of interest and facilitating more rigorous hypothesis testing. Its use will therefore aid researchers studying palaeoclimatic effects on prehistoric human societies as well as those studying the nature and effects of contemporary climate change. • Current definitions of climatic change and variability are often vague and subjective • An algorithm is designed that objectively decomposes a time series into change and variability components • An extensive series of simulations is employed to validate this algorithm • Two empirical case studies demonstrate its effectiveness [ABSTRACT FROM AUTHOR]

Rapid climate variability has been hypothesized to play an important role in hominin evolution, yet our knowledge of Plio-Pleistocene climate change on short timescales is poor. Here, we developed centennial-scale reconstructions of precipitation from leaf wax biomarker hydrogen isotope ratios (δD wax) using lacustrine sediment from West Turkana, Kenya. We analyzed two time intervals (∼1.72 and ∼1.60 Ma) with different orbital configurations (0.043 and 0.025 eccentricity, respectively) to examine the influence of seasonal insolation forcing on high-frequency climate variability and the rates of climate transitions. Our data indicate that under low summer insolation, which should induce high latitude glaciation and tropical African aridity, millennial-scale climate variability was stronger. This suggests that hominins may have been forced to contend with increased climate variability during already extreme environmental conditions. Additionally, we observe a rapid shift from arid to humid conditions occurring in less than 200 years under high-amplitude precessional-scale insolation change. The rate of this transition is similar to that observed in some proxy records of the onset of the African Humid Period, indicating high sensitivity to gradual insolation forcing in the Turkana Basin. Such abrupt climate changes could induce evolutionary selection for generalist behavioral traits in hominins. • High-resolution Turkana δD wax was measured in two early Pleistocene intervals. • High-frequency climate variability was strongest during low insolation times. • An abrupt, large-amplitude climate transition occurred during increasing insolation. • These changes may have influenced early human evolution and Acheulean innovation. [ABSTRACT FROM AUTHOR]

We challenge the view that our species, Homo sapiens , evolved within a single population and/or region of Africa. The chronology and physical diversity of Pleistocene human fossils suggest that morphologically varied populations pertaining to the H. sapiens clade lived throughout Africa. Similarly, the African archaeological record demonstrates the polycentric origin and persistence of regionally distinct Pleistocene material culture in a variety of paleoecological settings. Genetic studies also indicate that present-day population structure within Africa extends to deep times, paralleling a paleoenvironmental record of shifting and fractured habitable zones. We argue that these fields support an emerging view of a highly structured African prehistory that should be considered in human evolutionary inferences, prompting new interpretations, questions, and interdisciplinary research directions. [ABSTRACT FROM AUTHOR]

Lithic assemblages immediately following the Howiesons Poort, often loosely referred to as the 'post-Howiesons Poort' or MSA III, have attracted relatively little attention when compared to other well-known phases of the South African Middle Stone Age (MSA) sequence. Current evidence from sites occurring in widely-differing environments suggests that these assemblages are marked by temporal and technological variability, with few features in common other than the presence of unifacial points. Here we present a technological and geometric morphometric analysis of 'points' from the new excavations of Members 2 BS, 2 WA and the top of 3 BS members at Border Cave, KwaZulu-Natal, one of the key sites for studying modern human cultural evolution. Our complementary methodologies demonstrate that, at this site, hominins adopted a knapping strategy that primarily produced non-standardised unretouched points. Triangular morphologies were manufactured using a variety of reduction strategies, of which the discoidal and Levallois recurrent centripetal methods produced distinctive morphologies. We find technological and morphological variability increases throughout the post-Howiesons Poort sequence, with clear differences between and within chrono-stratigraphic groups. Finally, we assess the suitability of the 'Sibudan' cultural-technological typology proposed for post-Howiesons Poort assemblages at Sibhudu, another KwaZulu-Natal site, and find similarities in the morphological axes characterising the samples, despite differences in the shaping strategies adopted. Overall, our work contributes to the growing body of research that is helping to address historical research biases that have slanted our understanding of cultural evolution during the MSA of southern Africa towards the Still Bay and Howiesons Poort technocomplexes. • Points from post-Howiesons Poort layers at Border Cave are manufactured via diverse reduction sequences that produce triangular blanks. • Technological choices, i.e., knapping modality, orientation of the tip and retouch, influence gross point morphology. • Diagnostic Sibudan morphotypes can be distinguished within the Border Cave sample to an extent, despite notable technological differences. • Qualitative and quantitative assessment of technology and form provide a nuanced methodology for analysing lithic production strategies. [ABSTRACT FROM AUTHOR]

The hypothesis of a connection between the onset (or intensification) of Northern Hemisphere Glaciation, the stepwise increase in African aridity (and climate variability), and an important mammalian (including hominin) species turnover is a textbook example of the initiation of a scientific idea and its propagation in science. It is, however, also an example of the persistent popularity of a hypothesis despite mounting evidence against it. A critical review of key publications on the topic and statistical re-analysis of key records of global ice volume and African climate leads to three conclusions: (1) The Northern Hemisphere Glaciation was a gradual process occurring between ∼3.5 and 2.5 Ma, not a single event at ∼2.8 Ma or at any other time. (2) A consistent stepwise (+/−0.2 Ma) transition toward greater aridity in Africa at ∼2.8 Ma does not exist; instead, there are regionally different, gradual transitions partly in connection with the intensification of the Northern Hemisphere Glaciation, but above all with the establishment of the tropical Walker Circulation after ∼2 Ma. (3) Mammalian (including hominin) species turnovers at this time also appear to have been gradual, rather than stepwise. • We falsified the hypothesis of a connection between Northern Hemisphere Glaciation, African climate and human evolution. [ABSTRACT FROM AUTHOR]