Workshop Background

The upcoming research conference "Paleoclimates and Human Evolution:" Integrating drilling research with paleoanthropology and other geological records," will be held Nov 17-20, 2005 at the Smithsonian Institution’s Conference and Research Center (CRC) in Front Royal, Virginia. The CRC is located in the Blue Ridge Mountains, about 1 hr drive from Washington, D.C. The meeting is sponsored by the US National Science Foundation (Sedimentary Geology and Paleobiology Program-Grant #EAR 0530405, & HOMINID Program-Grant # BCS-0218511), the Smithsonian Institution’s Human Origins Program and DOSECC, the US national consortium for continental scientific drilling.

Anthropologists and archaeologists interested in human evolution have long recognized climate and environmental change as potentially powerful driving forces shaping the evolution of our species and its close relatives. For example, since its foundation, research in African paleoanthropology has looked carefully at evidence for climate change in attempts to interpret major evolutionary transitions in both human physical evolution and culture (reviewed in Potts, 1998). In recent decades, hypotheses have been proposed linking specific climate transitions in the Neogene (for example, episodes of aridification) or changes in overall climate variability to either specific events in hominin physical evolution or broader bursts in diversification (e.g. Vrba  1988, 2000; Potts, 1996; Bobe et al, 2002; Bobe and Behrensmeyer 2004). (Figure 1)

Figure 1. Three hypotheses relating evolutionary and environmental change:

Hypothesis A: Evolutionary change (first vertical bar) is unconnected to environmental change. It takes place at any time, including intervals of environmental stability or low variability. Newly evolved traits may reflect, for instance, ongoing competition within or between species irrespective of environmental setting.

Hypothesis B: Evolutionary change (second vertical bar) is concentrated in relatively brief periods of directional environmental change (e.g., a stepped decrease in temperature or precipitation). Newly evolved traits or taxonomic turnover directly reflect the shift from one dominant habitat type to another.

Hypothesis C: Evolutionary change (third vertical bar) is concentrated in intervals of high environmental variability. New traits reflect greater adaptive versatility, and first/last appearances of taxa reflect increasing vicariance or resource variability during these intervals.

These hypotheses are ideally testable if the record of hominin fossils and behavioral artifacts were relatively continuous and if the samples were densest around the time of a shift in the direction or variability of environmental change.

Simultaneous with these developments there has been a tremendous growth in interest in documenting the history of climate change in those same regions of the continents where the human evolution story has been played out. Some of this growth has been spurred by interest in complementing the paleoanthropological record (e.g. Behrensmeyer et al., 2002; Bonnefille, 1980; Cerling, 1992; DeMenocal, 1995; DeMenocal and Bloemendal, 1995; Liutkus and Ashley, 2000; Quade, 2004). However much of the work has also been driven by other concerns, specifically the desire to understand climate dynamics in the tropics, the heat engine of our planet. Quaternary paleoclimatology has proceeded at a rapid pace, with numerous research teams attempting to document major changes in climate (especially humid-arid climate transitions) and link those changes to external forcing variables such as orbital parameters or teleconnections with ice sheet dynamics at higher latitudes (Street-Perrott and Perrott, 1993; DeMenocal 1996). These investigations initially focused mostly on understanding the relatively short-term changes associated with the transition from the last glacial maximum (latest Pleistocene) to the interglacial Holocene climates we experience today. Such records are most frequently collected from sediment cores from lakes and mires, although increasingly speleothem, ice and coral records have been used for these purposes. In the last decade, researchers working on African lakes have sought to extend the time scale over which paleoclimatology hypotheses can be tested, through the acquisition of longer and older sediment records. The IDEAL (International Decade of East African Lakes) program was centered around the long term goal of acquiring very long time series data sets through scientific drilling of some of the world’s oldest lakes, in the African Rift Valley (Johnson et al., 1990; Cohen et al., 2000 ). These goals are now being realized with the recent successful completion of GLAD-800 drilling efforts at Lake Bosumtwi (Ghana) and scientific drilling at Lake Malawi .

Scientific drill core records, whether from deep lacustrine or marine sites, offer some very appealing sources of information for the hominid paleoclimate community. Unlike outcrop records of terrestrial paleoenvironments, which typically are temporally discontinuous, the records from basinal depocenters hold a promise of very high resolution and long duration archives. Tropical lakes, with their long-recognized sensitivity to subtle changes in precipitation/evaporation ratios, and their frequent accumulation of annually varved deposits, are ideal for producing such records (Street-Perrott and Perrott, 1993, Johnson et al., 2002). Similarly high resolution records can be obtained from continental margin barred basins, where anoxia and varved sedimentary records often develop in tropical settings (Cariaco refs). The geometry of stratigraphic sequences observed in seismic reflection profiles from Afrotropical lakes demonstrates that these lakes have undergone remarkable fluctuations in lake level over time (hundreds of meters) at what appear to be orbital time scales  (Figures 2 and 3) (Lezzar et al., 1996; Cohen et al., 1997)

Figure 2.Seismic reflection profile from central L. Malawi suggesting 100kyr lake level and depositional cyclicity. Amost identical cyclicity is observed in seismic profiles from L. Tanganyika. Acoustic facies couplets (shown in brackets) are composed of lowstand generated canyon mouth fan deposits (low amplitude, discontinuous facies) and highstand hemipelagic facies (high amplitude, continuous facies). Figure courtesy of C. Scholz (see Cohen et al., 2000).

Figure 3. Estimated timing of lake cycles in Lake Tanganyika relative to the marine oxygen isotope record. These estimates are based on a combination of known thicknesses of sediment packages (from seismic data) and sedimentation rates observed in similar tectonostratigraphic settings in Late Pleistocene-Holocene core records from the same lake. From Cohen et al. (1997).

Recent field studies indicate the existence of potential drilling targets that could yield near-continuous sediment records from the Late Miocene to the present of African tropical climate change, given a sufficiently long (500-1000m) drill coring campaign (Cohen et al., 2004).

The conference organizers (Gail Ashley, Andy Cohen, Craig Feibel, Rick Potts, Kay Behrensmeyer and Jay Quade) believe the time is ripe to bring the human evolution, continental scientific drilling and broader paleoclimate communities together to discuss both what we currently know about climate and environmental history in the arena of human evolution from current records, and what we might usefully learn in this area from carefully targeted future drilling campaigns. We have planned a workshop to bring together a) paleoanthropologists, archaeologists and paleontologists interested in the evolution of hominins and their ecological communities, b) geologists who have worked closely with the paleoanthropological community, interpreting local and regional climate change from outcrop records associated with hominin fossil sites, and c) paleoclimatologists involved in collecting and interpreting sediment core records from shallow and deep drilling programs, both on the continents and in the oceans. We propose to focus this workshop primarily on the African record, since this is the region where the longest and most continuous records of human evolution are to be found.

Conference Objectives

Our goals for this workshop are to;

1) identify key scientific hypotheses linking human evolution to explicit climate or environmental change scenarios,

2) identify specific target regions for drilling and data sets from resultant cores that could be used to test those hypotheses, and

3) formulate strategies for linking such records with existing paleoclimate and paleoenvironmental records from outcrops or the deep sea.

References Cited

Behrensmeyer, A.K., Potts, R., Deino, A., and Ditchfield, P. 2002, Olorgessalie, Kenya: A million years in the life of a rift basin. In Renaut, R. (ed.) Sedimentation in Continental Rifts SEPM Special Publ.. 73:97-106.

Bobe, René and A. K. Behrensmeyer.  2004.  The expansion of grassland ecosystems in Africa in relation to mammalial evolution and the origin of the genus Homo.  Palaeogeography, Palaeoclimatology, Palaeoecology 207: 399-420.

Bobe, R., Behrensmeyer, A.K., and Chapman, R.E., 2002. Faunal change, environmental variability and late Pliocene hominin evolution. Jour. Human Evol. 42:475-497.

Bonnefille, R., 1980, Vegetation history of savanna in East Africa during the Plio-Pleistocene. Proc. 4th Intl. Palynol. Conf., Lucknow, India pp. 75-89.

Cerling, T.E., 1992, Development of grasslands and savannas in East Africa during the Neogene. Palaeogeog., Palaeoclim. Palaeoecol. 97:241-247.

Cohen, A.S., Lezzar, K.E., Tiercelin, J.-J. and Soreghan, M.R.  1997  New palaeogeographic and lake level reconstructions of Lake Tanganyika:  Implications for tectonic, climatic and biologic evolution in a rift lake.  Basin Research 9: 107-132.

Cohen, A.S., Scholz, C.A., and Johnson, T.C., 2000, The International Decade of East African Lakes (IDEAL) drilling initiative for the African great lakes.  Jour. Paleolimnology 24:231-235.

Cohen, A., Lezzar, K., Russell, J., Scholz, C., Tiercelin, J.J., Gans, C. and Helfrich, L 2004. The Lake Tanganyika accommodation zone structural highs: Probable archive of continuous Miocene to Recent paleoenvironmental and paleoclimatic information for East Africa. EOS AGU Ann. Mtg. Abstr. w/prog.

deMenocal, P.B., 1995,  Plio-Pleistocene African climate. Science 270:53-59.

deMenocal, P.B., 1996, Sensitivity of subtropical African and Asian climate to prescribed boundary condition changes: model limplications for the Plio-Pleistocene evolution of low-latitude climate. In Johnson, T.C., and Odada, E. (eds.) The Limnology, Climatology, and Paleoclimatology of the East African Lakes. Gordon and Breach, Amsterdam, pp. 57-77.

deMenocal, P.B. and Bloemendal, J., 1995, Plio-Pleistocene climatic variability in subtropical Africa and the paleoenvironment of hominid evolution: A combined data-model approach. In Vrba, E.S., Denton, G.H.,, Partridge, T.C., and Burckel, L.H., (eds.) Paleoclimate and Evolution, with Emphasis on Human Origins.  Yale Univ. Press, New Haven, pp. 385-424.

Johnson, T.C. and 10 others, 1990, IDEAL An International Decade for the East African Lakes. Workshop Report 1 on the Paleoclimatology of the African Rift Lakes. Duke Univ. Marine Lab. Tech. Report, 39pp.

Johnson, T. C., Brown, E. T., McManus, J., Barry, S., Barker, P. and Gasse, F., 2002. A high-resolution paleoclimate record spanning the past 25,000 years in southern East Africa. Science, v. 295, p. 113-114, 131-132.

Lezzar, K., Tiercelin, J.J., DeBatist, M., Cohen, A.S., Bandora, P., Van Rensberger, P., Le Turdu, C., Mifundu, W. and Klerkx, J.  1996  New seismic stratigraphy and Late Tertiary history of the North Tanganyika Basin, East African Rift System, deduced from multichannel and high resolution reflection seismic data and piston core evidence.  Basin Research 8: 1-28.

Liutkus, C.M., and Ashley, G., 2000, Short term climate changes and Milankovitch cyclicity at Olduvai Gorge, Tanzania; evidence from sedimentology and stable isotopes. GSA Ann. Mtg. Abstr. w/prog. 32:21.

Potts, R., 1996, Evolution and climate variability. Science 273:922-923.

Potts, R., 1998b. Environmental hypotheses of hominin evolution. Yrbk. Phys. Anthrop. 41, 93-136.

Reference:  R. Potts, in press. Environmental hypotheses of Pliocene human evolution. In: Hominin Environments in the East African Pliocene: an Assessment of the Faunal Evidence, edited by R. Bobe, Z. Alemseged, and A.K. Behrensmeyer. Kluwer, New York.

Quade, J., Levin, N., Semaw, S., Stout, D., Renne, P., Rogers, M., Simpson, M., 2004, Paleoenvironments of the earliest stone toolmakers, Gona, Ethiopia. GSA Bull. 116:1529-1544.

Street-Perrott, F.A., and Perrott, R.A., 1993, Holocene vegetatio, lake levels and climate of Africa. In Wright, H.E., Jr., Kutzbach, J.E., Webb, T., Ruddiman, W.F., Street-Perrott, F.A., and Bartlein, P.J., (eds.) Global Climates Since the Last Glacial Maximum. Univ. Minnesota Press, Minneapolis pp. 318-356.

Vrba, E.S., 1988 Late Pliocene climate events and hominid evolution. In Grine, F.E., (ed) Evolutionary History of the “Robust” Australopithicines. Aldine Press, N.Y., pp. 405-426.

Vrba, E. S., 2000, Major features of Neogene mammalian evolution in Africa. In Vrba, E., Denton ,G.H., Partridge, T.C., and Burckle, L.H. (eds.) The Cenozoic of Southern Africa. Oxford Univ. Press, pp. 277-304.