ScienceDaily (June 8, 2010) — If you think summer in your hometown is hot, consider it fortunate that you don't live in the Turkana Basin of Kenya, where the average daily temperature has reached the mid-90s or higher, year-round, for the past 4 million years.
Lake Turkana, Kenya. (Credit: iStockphoto/Markus Karner)
"The 'take home' message of our study," said Passey, whose report appears in the online early edition ofProceedings of the National Academy of Sciences, "is that this region, which is one of the key places where fossils have been found documenting human evolution, has been a really hot place for a really long time, even during the period between 3 million years ago and now when the ice ages began and the global climate became cooler."
Passey, an assistant professor in the Morton K. Blaustein Department of Earth and Planetary Sciences at the university's Zanvyl Krieger School of Arts and Sciences, says that conclusion lends support to the so-called "thermal hypothesis" of human evolution.
That hypothesis states that our pre-human ancestors gained an evolutionary advantage in walking upright because doing so was cooler (when it is sunny, the near-surface air is warmer than air a few feet above the ground) and exposed their body mass to less sunlight than did crawling on all fours. The loss of body hair (fur) and the ability to regulate body temperature through perspiration would have been other adaptations helpful for living in a warm climate, according to the hypothesis.
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Benjamin H. Passey a,1,2, Naomi E. Levin a,1, Thure E. Cerling b, Francis H. Brown b, and John M. Eiler a
-Author Affiliations
aDivision of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125; and
bDepartment of Geology and Geophysics, University of Utah, Salt Lake City, UT 84112
↵1Present address: Department of Earth and Planetary Sciences, Johns Hopkins University, 301 Olin Hall, 3400 North Charles Street, Baltimore, MD 21218.
Edited* by Karl K. Turekian, Yale University, New Haven, CT, and approved May 14, 2010 (received for review February 12, 2010)
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 13C-18O 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.
continental paleoclimate clumped isotopes soil temperature hominid bipedal locomotion
Footnotes
2To whom correspondence should be addressed. E-mail: bhpassey@jhu.edu.
Author contributions: B.H.P., N.E.L., T.E.C., F.H.B., and J.M.E. designed research; B.H.P., N.E.L., T.E.C., F.H.B., and J.M.E. performed research; B.H.P., N.E.L., T.E.C., F.H.B., and J.M.E. analyzed data; and B.H.P. wrote the paper.
The authors declare no conflict of interest.
↵*This Direct Submission article had a prearranged editor.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1001824107/-/DCSupplemental.
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NOTA CAUSTICANTE DESTE BLOGGER:
Gente, eu nem sei como emitir aqui uma nota causticante. Sa be por que? Porque a evolução é mais inteligente do que você, Enézio, idiota! Se não anunciarmos o fato, Fato, FATO da evolução, as pedras clamarão! E as pedras da Etiópia fizeram justamente: os pré-humanos perderam os pelos por causa do calor escorchante e era uma vantagem evolutiva perder os pelos que outrora tinha sido uma vantagem evolutiva, entendeu? Eu? Não entendi bulhufas. E os caras são da do Caltech, Universidade de Hopkins e da Universidade de Utah. Tutti buona gente, capice?
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