Early hominid habitat preferences in East Africa: Paleosol carbon isotopic evidence

Sikes, Nancy E.

doi:10.1006/jhev.1994.1034

Cited by 132 publications

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“…The discontinuous ground cover in closed canopy forest and near-closed canopy woodland is dominated by C3 herbs and shrubs. This classification of savanna vegetation has been used to describe and sample modern plants and soils, and is consistent with prior reconstructions of vegetation communities based on buried Holocene age or older pedogenic carbonate or organic S^^C values Cerling et al, 1991;Cerling, 1992;Sikes, 1994Sikes, , 1995Sikes, , 1996Sikes et al, 1997Sikes et al, , 1999. A similar classification scheme, also used to interpret paleovegetation from isotopic data (e.g., Wynn, 2000), combines terminology developed by Cole (1963) with annual precipitation and soil drainage and texture to explain the distribution of savanna types (Johnson and Tothill, 1984;Belsky, 1990;Owen-Smith, 1999).…”

Section: Soil Stable Isotope Valuessupporting

confidence: 65%

“…Pedogenic carbonate and organic matter 8^^C values have thus been used to 1) determine the proportion of C4 biomass (0 to 100%) contributing to soil CO2 and 2) differentiate between standard physiognomic types of tropical plant communities in East Africa (e.g., Cerling, 1992;Kingston et al, 1994;Sikes, 1994Sikes, , 1995Sikes et al, 1999). The 5"C values of these two soil components increase as tree cover decreases and C4 biomass increases.…”

Section: Soil Stable Isotope Valuesmentioning

confidence: 99%

“…During the past 30 years this method of environmental reconstruction has been applied to early hominin and hominoid localities in East Africa (e.g., Cerling et al, 1977Cerling et al, , 1988Cerling and Hay, 1986;Cerling, 1992;Kingston et al, 1994;Sikes, 1994Sikes, , 1996Sikes, , 2000Sikes et al, 1997Sikes et al, , 1999and summarized in Sikes, 1999), as well as other time periods and areas worldwide (e.g., Quade et al, 1989aQuade et al, , 1995Smith et al, 1993;Alam et al, 1997). Pedogenic carbonate and organic 8^^C values represent many generations of plants, averaged over the lifetime of a soil (hundreds or thousands of years).…”

Section: Soil Stable Isotope Valuesmentioning

confidence: 99%

“…4B,8,9). This interpretation of the range of 8^^C values for the Bed I paleosols is based on comparison to modern East African soil datasets and corresponding vegetation communities (Cerling, 1992;Sikes, 1994Sikes, , 1995. The analog data indicate C4 biomass may be interpreted as percent grass or percent ground cover since, in these two standard types of vegetational savanna, tropical C4 grasses dominate the continuous herbaceous layer.…”

Section: Paleoecologymentioning

confidence: 99%

“…The widely spaced samples of these microstratigraphic units exposed in the trenches also enable us to examine lateral variation in the local physical or biological features of the paleolandscapes. We use the stable oxygen and carbon isotope values preserved within the carbonate and/or organic components of paleosols (buried soils) to reconstruct local climatic conditions and variation in tropical vegetation communities with different proportions of grasses (C4) to woody (C3) vegetation (e.g., Sikes, 1994Sikes, , 1996Sikes et al, 1999). This approach recognizes that not even a single paleosol is equivalent to an actual landscape because of the effects of time-averaging (e.g., Potts et al, 1999;Sikes et al, 1999).…”

Section: Introductionmentioning

confidence: 99%

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Stable isotopes of pedogenic carbonates as indicators of paleoecology in the Plio-Pleistocene (upper Bed I), western margin of the Olduvai Basin, Tanzania

Sikes

Ashley

2007

Journal of Human Evolution

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Section: Soil Stable Isotope Valuessupporting

confidence: 65%

Section: Soil Stable Isotope Valuesmentioning

confidence: 99%

Section: Soil Stable Isotope Valuesmentioning

confidence: 99%

Section: Paleoecologymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Stable isotopes of pedogenic carbonates as indicators of paleoecology in the Plio-Pleistocene (upper Bed I), western margin of the Olduvai Basin, Tanzania

Sikes

Ashley

2007

Journal of Human Evolution

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Environmental hypotheses of hominin evolution

Potts

1998

Am. J. Phys. Anthropol.

413

208

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The study of human evolution has long sought to explain major adaptations and trends that led to the origin of Homo sapiens. Environmental scenarios have played a pivotal role in this endeavor. They represent statements or, more commonly, assumptions concerning the adaptive context in which key hominin traits emerged. In many cases, however, these scenarios are based on very little if any data about the past settings in which early hominins lived. Several environmental hypotheses of human evolution are presented in this paper. Explicit test expectations are laid out, and a preliminary assessment of the hypotheses is made by examining the environmental records of Olduvai, Turkana, Olorgesailie, Zhoukoudian, Combe Grenal, and other hominin localities. Habitat-specific hypotheses have prevailed in almost all previous accounts of human adaptive history. The rise of African dry savanna is often cited as the critical event behind the development of terrestrial bipedality, stone toolmaking, and encephalized brains, among other traits. This savanna hypothesis has been countered recently by the woodland/forest hypothesis, which claims that Pliocene hominins had evolved in and were primarily attracted to closed habitats. The ideas that human evolution was fostered by cold habitats in higher latitudes or by seasonal variations in tropical and temperate zones also have their proponents. An alternative view, the variability selection hypothesis, states that large disparities in environmental conditions were responsible for important episodes of adaptive evolution. The resulting adaptations enhanced behavioral versatility and ultimately ecological diversity in the human lineage. Global environmental records for the late Cenozoic and specific records at hominin sites show the following: 1) early human habitats were subject to large-scale remodeling over time; 2) the evidence for environmental instability does not support habitat-specific explanations of key adaptive changes; 3) the range of environmental change over time was more extensive and the tempo far more prolonged than allowed by the seasonality hypothesis; and 4) the variability selection hypothesis is strongly supported by the persistence of hominins through long sequences of environmental remodeling and the origin of important adaptations in periods of wide habitat diversity. Early bipedality, stone transport, diversification of artifact contexts, encephalization, and enhanced cognitive and social functioning all may reflect adaptations to environmental novelty and highly varying selective contexts.

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Variability selection in hominid evolution

Potts¹

1998

Evol. Anthropol.

437

146

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Variability selection (abbreviated as VS) is a process considered to link adaptive change to large degrees of environment variability. Its application to hominid evolution is based, in part, on the pronounced rise in environmental remodeling that took place over the past several million years. The VS hypothesis differs from prior views of hominid evolution, which stress the consistent selective effects associated with specific habitats or directional trends (e.g., woodland, savanna expansion, cooling). According to the VS hypothesis, wide fluctuations over time created a growing disparity in adaptive conditions. Inconsistency in selection eventually caused habitat‐specific adaptations to be replaced by structures and behaviors responsive to complex environmental change. Key hominid adaptations, in fact, emerged during times of heightened variability. Early bipedality, encephalized brains, and complex human sociality appear to signify a sequence of VS adaptations—i.e., a ratcheting up of versatility and responsiveness to novel environments experienced over the past 6 million years. The adaptive results of VS cannot be extrapolated from selection within a single environmental shift or relatively stable habitat. If some complex traits indeed require disparities in adaptive setting (and relative fitness) in order to evolve, the VS idea counters the prevailing view that adaptive change necessitates long‐term, directional consistency in selection. © 1998 Wiley‐Liss, Inc.

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Early hominid habitat preferences in East Africa: Paleosol carbon isotopic evidence

Cited by 132 publications

References 0 publications

Stable isotopes of pedogenic carbonates as indicators of paleoecology in the Plio-Pleistocene (upper Bed I), western margin of the Olduvai Basin, Tanzania

Stable isotopes of pedogenic carbonates as indicators of paleoecology in the Plio-Pleistocene (upper Bed I), western margin of the Olduvai Basin, Tanzania

Environmental hypotheses of hominin evolution

Variability selection in hominid evolution

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