Grassed up
A cherished theory about why people walk upright has just bitten the dust
Feb 16th 2013 |From the print edition
AFRICA’S great grasslands are one of that continent’s most famous features. They are also reckoned by many to have been crucial to human evolution. This school of thought holds that people walk upright because their ancestors could thus see farther on an open plain. Forest primates do not need to be bipedal, the argument continues, because the trees limit their vision anyway.
As “Just So” stories go, it is perfectly plausible. But some go further and argue that the transition took place when the savannahs themselves came into existence, replacing the pre-existing forest and forcing human ancestors to adapt or die out. Fossil evidence suggests humanity’s upright stance began to evolve between 6m and 4m years ago. So the question is, did that coincide with the formation of the savannah? A paper in Geology, by Sarah Feakins, of the University of Southern California, suggests not.
Dr Feakins studied sediment cores from the Gulf of Aden, a place where offshore winds deposit detritus from a goodly part of the east of the African continent. In these, she discovered plant molecules that date back between 12m and 1m years. Such molecules contain carbon, and carbon atoms come in various isotopes, whose ratios give away their history. In particular, the ratio of ¹²C to ¹³C can tell you what sort of plant made the molecule in question.
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Read more here/Leia mais aqui: The Economist
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Northeast African vegetation change over 12 m.y.
Sarah J. Feakins1,*, Naomi E. Levin2, Hannah M. Liddy1, Alexa Sieracki1, Timothy I. Eglinton3 and Raymonde Bonnefille4
- Author Affiliations
1Department of Earth Sciences, University of Southern California, 3651 Trousdale Parkway, Los Angeles, California 90089-0740, USA
2Department of Earth and Planetary Sciences, Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland 21218, USA
3Geological Institute, Department of Earth Sciences, Sonneggstrasse 5, Eidgenössische Technische Hochschule (ETH—Swiss Federal Institute of Technology), Zurich, CH-8092 Zürich, Switzerland
4CEREGE, Centre National de la Recherche Scientifique, Université d’Aix-Marseille, B.P. 80, F 13545 Aix-en-Provence, cedex 04, France
↵*E-mail: feakins@usc.edu.
Abstract
Intense debate surrounds the evolution of grasses using the C4 (Hatch-Slack) photosynthesis pathway and the emergence of African grasslands, often assumed to be one and the same. Here, we bring new insights with the combination of plant leaf wax carbon isotopic composition (δ13Cwax) and pollen data from marine sediments of the Gulf of Aden (northeast Africa), which show that C4 biomass increases were not necessarily associated with regional grassland expansion. We find broadly opposing trends toward more enriched δ13Cwax values and decreased grass pollen proportions between 12 and 1.4 Ma. This apparently contradictory evidence can be reconciled if a greater proportion of the Late Miocene northeast African landscape were covered by C3 grasses than previously thought, such that C4 grasses and shrubs replaced a C3 ecosystem including trees and productive grasslands. In addition, δ13Cwax and pollen both indicate that true rainforests were unlikely to have been extensive in northeast Africa at any time in the last 12 m.y., although seasonally dry forests were a significant component of the regional landscape since the Late Miocene. Here, we extend regionally integrative marine archives of terrestrial vegetation back to 12 Ma, and we evaluate them in the context of an updated compilation of pedogenic carbonate δ13C values from East African Rift strata. We identify two distinct phases of increasing C4 biomass between 11 and 9 Ma (with a reversal by 4.3 Ma) and then a re-expansion between 4.3 and 1.4 Ma; surprisingly, neither was associated with grassland expansion.
Received 19 July 2012.
Revision received 18 September 2012.
Accepted 18 September 2012.
© 2013 Geological Society of America
FREE PDF GRATIS
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Northeast African vegetation change over 12 m.y.
Sarah J. Feakins1,*, Naomi E. Levin2, Hannah M. Liddy1, Alexa Sieracki1, Timothy I. Eglinton3 and Raymonde Bonnefille4
- Author Affiliations
1Department of Earth Sciences, University of Southern California, 3651 Trousdale Parkway, Los Angeles, California 90089-0740, USA
2Department of Earth and Planetary Sciences, Johns Hopkins University, 3400 N. Charles Street, Baltimore, Maryland 21218, USA
3Geological Institute, Department of Earth Sciences, Sonneggstrasse 5, Eidgenössische Technische Hochschule (ETH—Swiss Federal Institute of Technology), Zurich, CH-8092 Zürich, Switzerland
4CEREGE, Centre National de la Recherche Scientifique, Université d’Aix-Marseille, B.P. 80, F 13545 Aix-en-Provence, cedex 04, France
↵*E-mail: feakins@usc.edu.
Abstract
Intense debate surrounds the evolution of grasses using the C4 (Hatch-Slack) photosynthesis pathway and the emergence of African grasslands, often assumed to be one and the same. Here, we bring new insights with the combination of plant leaf wax carbon isotopic composition (δ13Cwax) and pollen data from marine sediments of the Gulf of Aden (northeast Africa), which show that C4 biomass increases were not necessarily associated with regional grassland expansion. We find broadly opposing trends toward more enriched δ13Cwax values and decreased grass pollen proportions between 12 and 1.4 Ma. This apparently contradictory evidence can be reconciled if a greater proportion of the Late Miocene northeast African landscape were covered by C3 grasses than previously thought, such that C4 grasses and shrubs replaced a C3 ecosystem including trees and productive grasslands. In addition, δ13Cwax and pollen both indicate that true rainforests were unlikely to have been extensive in northeast Africa at any time in the last 12 m.y., although seasonally dry forests were a significant component of the regional landscape since the Late Miocene. Here, we extend regionally integrative marine archives of terrestrial vegetation back to 12 Ma, and we evaluate them in the context of an updated compilation of pedogenic carbonate δ13C values from East African Rift strata. We identify two distinct phases of increasing C4 biomass between 11 and 9 Ma (with a reversal by 4.3 Ma) and then a re-expansion between 4.3 and 1.4 Ma; surprisingly, neither was associated with grassland expansion.
Received 19 July 2012.
Revision received 18 September 2012.
Accepted 18 September 2012.
© 2013 Geological Society of America
FREE PDF GRATIS
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NOTA DESTE BLOGGER:
AlÔ MEC/SEMTEC/PNLD: Corrijam isso nas próximas edições dos livros texto de Biologia recomendados em 2012. Aliás, os professores deveriam receber notas de retificação dos autores todas as vezes que a teoria da evolução de Darwin não for justificada no contexto de justificação teórica.
Que o exemplo de jornalismo científico do The Economist encontre eco na Grande Mídia Tupiniquim que não tem cojones para apontar a falência epistêmica da teoria da evolução de Darwin através da seleção natural e n mecanismos evolucionários - de A a Z.
Pano rápido, mais uma teoria sobre o bipedalismo vai para a lata de lixo da História da Ciência.
Que o exemplo de jornalismo científico do The Economist encontre eco na Grande Mídia Tupiniquim que não tem cojones para apontar a falência epistêmica da teoria da evolução de Darwin através da seleção natural e n mecanismos evolucionários - de A a Z.
Pano rápido, mais uma teoria sobre o bipedalismo vai para a lata de lixo da História da Ciência.
Chupa essa Nomenklatura científica e Galera de meninos e meninas de Darwin!
