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  • 1
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    Online Resource
    Aridity and hominin environments
    Proceedings of the National Academy of Sciences ; 2017
    In:  Proceedings of the National Academy of Sciences Vol. 114, No. 28 ( 2017-07-11), p. 7331-7336
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 114, No. 28 ( 2017-07-11), p. 7331-7336
    Abstract: Aridification is often considered a major driver of long-term ecological change and hominin evolution in eastern Africa during the Plio-Pleistocene; however, this hypothesis remains inadequately tested owing to difficulties in reconstructing terrestrial paleoclimate. We present a revised aridity index for quantifying water deficit (WD) in terrestrial environments using tooth enamel δ 18 O values, and use this approach to address paleoaridity over the past 4.4 million years in eastern Africa. We find no long-term trend in WD, consistent with other terrestrial climate indicators in the Omo-Turkana Basin, and no relationship between paleoaridity and herbivore paleodiet structure among fossil collections meeting the criteria for WD estimation. Thus, we suggest that changes in the abundance of C 4 grass and grazing herbivores in eastern Africa during the Pliocene and Pleistocene may have been decoupled from aridity. As in modern African ecosystems, other factors, such as rainfall seasonality or ecological interactions among plants and mammals, may be important for understanding the evolution of C 4 grass- and grazer-dominated biomes.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.1700597114
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    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2017
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  • 2
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    Woody cover and hominin environments in the past 6 million years
    Springer Science and Business Media LLC ; 2011
    In:  Nature Vol. 476, No. 7358 ( 2011-8), p. 51-56
    Details
    In: Nature, Springer Science and Business Media LLC, Vol. 476, No. 7358 ( 2011-8), p. 51-56
    Type of Medium: Online Resource
    ISSN: 0028-0836 , 1476-4687
    URL: Article
    DOI: 10.1038/nature10306
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    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2011
    detail.hit.zdb_id: 120714-3
    detail.hit.zdb_id: 1413423-8
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  • 3
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    Environmental dynamics during the onset of the Middle Stone Age in eastern Africa
    American Association for the Advancement of Science (AAAS) ; 2018
    In:  Science Vol. 360, No. 6384 ( 2018-04-06), p. 86-90
    Details
    In: Science, American Association for the Advancement of Science (AAAS), Vol. 360, No. 6384 ( 2018-04-06), p. 86-90
    Abstract: Development of the African Middle Stone Age (MSA) before 300,000 years ago raises the question of how environmental change influenced the evolution of behaviors characteristic of early Homo sapiens . We used temporally well-constrained sedimentological and paleoenvironmental data to investigate environmental dynamics before and after the appearance of the early MSA in the Olorgesailie basin, Kenya. In contrast to the Acheulean archeological record in the same basin, MSA sites are associated with a markedly different faunal community, more pronounced erosion-deposition cycles, tectonic activity, and enhanced wet-dry variability. Aspects of Acheulean technology in this region imply that, as early as 615,000 years ago, greater stone material selectivity and wider resource procurement coincided with an increased pace of land-lake fluctuation, potentially anticipating the adaptability of MSA hominins.
    Type of Medium: Online Resource
    ISSN: 0036-8075 , 1095-9203
    URL: Article
    DOI: 10.1126/science.aao2200
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    Language: English
    Publisher: American Association for the Advancement of Science (AAAS)
    Publication Date: 2018
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  • 4
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    High-temperature environments of human evolution in East Africa based on bond ordering in paleosol carbonates
    Proceedings of the National Academy of Sciences ; 2010
    In:  Proceedings of the National Academy of Sciences Vol. 107, No. 25 ( 2010-06-22), p. 11245-11249
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 107, No. 25 ( 2010-06-22), p. 11245-11249
    Abstract: Many important hominid-bearing fossil localities in East Africa are in regions that are extremely hot and dry. Although humans are well adapted to such conditions, it has been inferred that East African environments were cooler or more wooded during the Pliocene and Pleistocene when this region was a central stage of human evolution. Here we show that the Turkana Basin, Kenya—today one of the hottest places on Earth—has been continually hot during the past 4 million years. The distribution of 13 C- 18 O bonds in paleosol carbonates indicates that soil temperatures during periods of carbonate formation were typically above 30 °C and often in excess of 35 °C. Similar soil temperatures are observed today in the Turkana Basin and reflect high air temperatures combined with solar heating of the soil surface. These results are specific to periods of soil carbonate formation, and we suggest that such periods composed a large fraction of integrated time in the Turkana Basin. If correct, this interpretation has implications for human thermophysiology and implies a long-standing human association with marginal environments.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.1001824107
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    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2010
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  • 5
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    Dietary changes of large herbivores in the Turkana Basin, Kenya from 4 to 1 Ma
    Proceedings of the National Academy of Sciences ; 2015
    In:  Proceedings of the National Academy of Sciences Vol. 112, No. 37 ( 2015-09-15), p. 11467-11472
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 112, No. 37 ( 2015-09-15), p. 11467-11472
    Abstract: A large stable isotope dataset from East and Central Africa from ca . 30 regional collection sites that range from forest to grassland shows that most extant East and Central African large herbivore taxa have diets dominated by C 4 grazing or C 3 browsing. Comparison with the fossil record shows that faunal assemblages from ca . 4.1–2.35 Ma in the Turkana Basin had a greater diversity of C 3 –C 4 mixed feeding taxa than is presently found in modern East and Central African environments. In contrast, the period from 2.35 to 1.0 Ma had more C 4 -grazing taxa, especially nonruminant C 4 -grazing taxa, than are found in modern environments in East and Central Africa. Many nonbovid C 4 grazers became extinct in Africa, notably the suid Notochoerus , the hipparion equid Eurygnathohippus , the giraffid Sivatherium , and the elephantid Elephas . Other important nonruminant C 4 -grazing taxa switched to browsing, including suids in the lineage Kolpochoerus - Hylochoerus and the elephant Loxodonta . Many modern herbivore taxa in Africa have diets that differ significantly from their fossil relatives. Elephants and tragelaphin bovids are two groups often used for paleoecological insight, yet their fossil diets were very different from their modern closest relatives; therefore, their taxonomic presence in a fossil assemblage does not indicate they had a similar ecological function in the past as they do at present. Overall, we find ecological assemblages of C 3 -browsing, C 3 –C 4 -mixed feeding, and C 4 -grazing taxa in the Turkana Basin fossil record that are different from any modern ecosystem in East or Central Africa.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.1513075112
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    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2015
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  • 6
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    A stable isotope aridity index for terrestrial environments
    Proceedings of the National Academy of Sciences ; 2006
    In:  Proceedings of the National Academy of Sciences Vol. 103, No. 30 ( 2006-07-25), p. 11201-11205
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 103, No. 30 ( 2006-07-25), p. 11201-11205
    Abstract: We use the oxygen isotopic composition of tooth enamel from multiple mammalian taxa across eastern Africa to present a proxy for aridity. Here we report tooth enamel δ 18 O values of 14 species from 18 locations and classify them according to their isotopic sensitivity to environmental aridity. The species are placed into two groups, evaporation sensitive (ES) and evaporation insensitive (EI). Tooth enamel δ 18 O values of ES animals increase with aridity, whereas the tooth enamel δ 18 O values of EI animals track local meteoric water δ 18 O values, demonstrating that bioapatite δ 18 O values of animals with different behaviors and physiologies record different aspects of the same environment. The enrichment between tooth enamel δ 18 O values of ES and EI animals records the degree of 18 O enrichment between evaporated water (ingested water or body water) and source water, which increases with environmental aridity. Recognition of the ES–EI distinction creates the opportunity to use the 18 O composition of bioapatite as an index of terrestrial aridity.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.0604719103
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    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2006
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  • 7
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    Comment on the Paleoenvironment of Ardipithecus ramidus
    American Association for the Advancement of Science (AAAS) ; 2010
    In:  Science Vol. 328, No. 5982 ( 2010-05-28), p. 1105-1105
    Details
    In: Science, American Association for the Advancement of Science (AAAS), Vol. 328, No. 5982 ( 2010-05-28), p. 1105-1105
    Abstract: White and colleagues (Research Articles, 2 October 2009, pp. 65–67 and www.sciencemag.org/ardipithecus ) characterized the paleoenvironment of Ardipithecus ramidus at Aramis, Ethiopia, which they described as containing habitats ranging from woodland to forest patches. In contrast, we find the environmental context of Ar. ramidus at Aramis to be represented by what is commonly referred to as tree- or bush-savanna, with 25% or less woody canopy cover.
    Type of Medium: Online Resource
    ISSN: 0036-8075 , 1095-9203
    URL: Article
    DOI: 10.1126/science.1185274
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    Language: English
    Publisher: American Association for the Advancement of Science (AAAS)
    Publication Date: 2010
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  • 8
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    New species from Ethiopia further expands Middle Pliocene hominin diversity
    Springer Science and Business Media LLC ; 2015
    In:  Nature Vol. 521, No. 7553 ( 2015-05-28), p. 483-488
    Details
    In: Nature, Springer Science and Business Media LLC, Vol. 521, No. 7553 ( 2015-05-28), p. 483-488
    Type of Medium: Online Resource
    ISSN: 0028-0836 , 1476-4687
    URL: Article
    DOI: 10.1038/nature14448
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    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2015
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  • 9
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    Decision versus compromise for animal groups in motion
    Proceedings of the National Academy of Sciences ; 2012
    In:  Proceedings of the National Academy of Sciences Vol. 109, No. 1 ( 2012-01-03), p. 227-232
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 109, No. 1 ( 2012-01-03), p. 227-232
    Abstract: Previously, we showed using a computational agent-based model that a group of animals moving together can make a collective decision on direction of motion, even if there is a conflict between the directional preferences of two small subgroups of “informed” individuals and the remaining “uninformed” individuals have no directional preference. The model requires no explicit signaling or identification of informed individuals; individuals merely adjust their steering in response to socially acquired information on relative motion of neighbors. In this paper, we show how the dynamics of this system can be modeled analytically, and we derive a testable result that adding uninformed individuals improves stability of collective decision making. We first present a continuous-time dynamic model and prove a necessary and sufficient condition for stable convergence to a collective decision in this model. The stability of the decision, which corresponds to most of the group moving in one of two alternative preferred directions, depends explicitly on the magnitude of the difference in preferred directions; for a difference above a threshold the decision is stable and below that same threshold the decision is unstable. Given qualitative agreement with the results of the previous simulation study, we proceed to explore analytically the subtle but important role of the uninformed individuals in the continuous-time model. Significantly, we show that the likelihood of a collective decision increases with increasing numbers of uninformed individuals.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.1118318108
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    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2012
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  • 10
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    Uninformed Individuals Promote Democratic Consensus in Animal Groups
    American Association for the Advancement of Science (AAAS) ; 2011
    In:  Science Vol. 334, No. 6062 ( 2011-12-16), p. 1578-1580
    Details
    In: Science, American Association for the Advancement of Science (AAAS), Vol. 334, No. 6062 ( 2011-12-16), p. 1578-1580
    Abstract: Conflicting interests among group members are common when making collective decisions, yet failure to achieve consensus can be costly. Under these circumstances individuals may be susceptible to manipulation by a strongly opinionated, or extremist, minority. It has previously been argued, for humans and animals, that social groups containing individuals who are uninformed, or exhibit weak preferences, are particularly vulnerable to such manipulative agents. Here, we use theory and experiment to demonstrate that, for a wide range of conditions, a strongly opinionated minority can dictate group choice, but the presence of uninformed individuals spontaneously inhibits this process, returning control to the numerical majority. Our results emphasize the role of uninformed individuals in achieving democratic consensus amid internal group conflict and informational constraints.
    Type of Medium: Online Resource
    ISSN: 0036-8075 , 1095-9203
    URL: Article
    DOI: 10.1126/science.1210280
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    Language: English
    Publisher: American Association for the Advancement of Science (AAAS)
    Publication Date: 2011
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