Glynn Isaac

Radiocarbon Dating of East African Lake Levels

The fluctuations of the key East African lakes discussed are summarized in Fig. 4 which also includes the available evidence from Lake Rukwa (42) and Lake Chad (43) Exceot for Lake Victoria, all of these now lack surface outlets and are situated in much drier climates than the major lakes of the Western Rift Valley, which remain filled to their overflow levels. The apparent differendes among the fluctuations of the lakes are partly due to differendes in the nature of the evidence or the intensity of research or both, although there must also have been important local differences in the histories of the lakes Yet the consistencies are far more striking, most notably the coincidence of early Holocene high stands. Between 10,000 and 8,000 years ago, it seems that lakes in many parts of tropical Africa were greatly enlarged. Where evidence for the previous span of time is well resolved, it appears that transgressions leading to this high stand began about 12,000 years ago, and evidende from three basins (Victoria, Nakuru, and Chad) indicates a pause or minor recession just at or before 10,000 years ago. Wherever information is available for the period preceding 12,000 years ago, it can consistentlybe shown that lakes were much small-er . Several basins (Rudolf, Nakuru, and Chad) also show traces of much earlier phases of lake expansion. which are not yet well dated but which all occurred more then 20,000 years ago. The Holocene record subsequent to the maximum of 10,00 to 8,000 years ago is more complex. Three basins (Rudolf, Nakuru, and Chad) show an apparently concordant, positive oscillation at some point between 6000 and 4000 years ago, but it is uncertain how widely this episode is represented. Although many of these lakes that are now closed filled to overflowing at least once during the late Quaternary, it is evident from Fig. 4 that the periods of expansion were short-lived compared with phases of contraction to levels near those of today. This pattern may be in accord with fragmentary evidence from lower and middle Pleistocene formations, such as those of Olduvai(44)and Paninj (45), within which some relatively short-term lake expansions can be documented, but which lack evidence for any marked long-term departure from a balance of evaporation and precipitation similar to the present one Further, this pattern of brief moist pulsations, with a duration of perhaps 2000 to 5000 years, is also suggested by other late Pleistocene and Holocene sequences (based primarily on geomorphological and palynological evidence) from the Saharan area, Angola, and South Africa (46). In default of radiometric dating, such complex successions of relatively brief moist intervals provide few stratigraphic markers of broad applicability. This, together with the fact that vegetation, weathering processes, montane glaciers, lake size, lake salinity, and so forth are all likely to reflect the diverse aspects of Climatic change differently, underscores the strictures of Cooke (2) and Flint (3) against the use of pluvials and intrlvasas a basis for subdividing Quaternary time in Africa. Positive correlations between high-latitude glacial advances or maxima and intervals of high lake levels have been demonstrated or suggested for many areas of mid-latitude North America and Eurasia (47), and similar patterns have often been regarded as probable for tropical Africa as well. However, the evidence summarized above shows a notable lack of such correlations for the tropical lakes considered here. If glaciation and tropical lake levels were connected at all, then a far more complex-delayed, multiplefactor, or inverse-relationship must be sought for the late Quaternary (48). This renders the introduction of new climato-stratigraphic terms such as hypothermal and interstadial (49) of questionable value in East Africa. Further, whereas the so-called pluvial lakes of higher latitudes were probably due primarily to reduced evaporation (50), our computations for the early Holocene lakes Nakuru and Naivasha, as well as for the oscillations of Lake Rudolf and Lake Victoria in recent decades, suggest that many or most of the high tropical lake levels where associated with a modest but significant increase in precipitation.

FxJj50: An early Pleistocene site in northern Kenya

Abstract Excavation in the Upper Member of the Koobi Fora Formation in Kenya has revealed a cluster of stone artefacts and broken up bones which accumulated 1–5 million years ago on the banks of a water course. The assemblage had been preserved by layers of silt. The stone artefacts consist of flakes and flake fragments plus simple flaked cobbles. It has been possible to conjoin individual pieces linking about 10 per cent of the artefacts and 4 per cent of the identifiable bones in pairs or sets. In some cases it seems likely that the specimens were fractured on the spot. Some of the fracture patterns on the bones suggest breakage with hammers, and apparent cut marks have also been found on some bones. There are signs of the presence of scavenging carnivores as well as of tool‐making hominids, and both could have contributed to the workings of a complex input‐output system. Whether the site was a home‐base camp or simply a locality used for meat‐eating and tool‐making remains uncertain. Experimental work ...

The diet of early man: Aspects of archaeological evidence from lower and middle Pleistocene sites in Africa

Abstract Evidence for Palaeolithic diet is critically reviewed, especially that from African sites. Methods of evaluating it, and some of the resulting socio‐economic conclusions, are examined. Hominids, although their ancestral stock was largely vegetarian, have evolved so as to include more protein in their diet; its importance has varied, apparently increasing by latitudinal gradations from equator to pole. Flexible joint dependence on animal and plant foods, establishment of home bases, food sharing, and differentiation of the subsistence activities of the sexes, together constitute an integrated behavioural complex already partly established some two million years ago. Large animals are certainly represented in Lower Pleistocene food refuse; they become commoner in the Middle Pleistocene, when evidence for effective co‐operative large‐scale hunting also first occurs. Other Middle and Late Pleistocene developments, some dependent on the increased geographic range of hominid settlement, are briefly rev...

STAGES OF CULTURAL ELABORATION IN THE PLEISTOCENE: POSSIBLE ARCHAEOLOGICAL INDICATORS OF THE DEVELOPMENT OF LANGUAGE CAPABILITIES

Asking an archaeologist to discuss language is rather like asking a mole to describe life in the treetops. The earthy materials with which archaeologists deal contain no direct traces of the phenomena that figure so largely in a technical consideration of the nature of language. There are no petrified phonemes and no fossil grammars. The oldest actual relicts of language that archaeologists can put their hands on are no older than the first invention of writing systems some five or six thousand years ago. And yet the intricate physiological basis of language makes it perfectly clear that this human ability has deep roots, roots that may extend as far as, or farther back in time than, the documented beginnings of tool-making some two and a half million years ago. However, to return to the simile: if the forest has been cut down and all that remains are the roots, then the mole may not be such an inappropriate consultant. So it is with the history of language development. Comparative studies can indicate phylogenetic patterns, while detailed understanding of the structure and physiology of modern human linguistic capabilities can suggest possible successive stages of prehuman development; however, beyond a certain point, historical understanding demands dated evidence for successive developmental stages. This record, if it is to be obtained at all, must be sought from paleontologists and archaeologists. It is probable that the search is not quite as hopeless as it may look at first glance, but it is equally certain that there are no very simple answers. In my mind there stand out two possible lines of approach to the problem. The j r s t involves scrutiny of the record of developing protohuman material culture systems and consideration of its potential relevance to the problem in hand. Stone artefacts are the best and most persistant long-term markers, but during the last five percent of the time span, we can also deal with more fancy evidence such as burials, ornaments, art, notations, cult objects, structures, and so forth. The second approach involves taking archaeological evidence which is indicative of the economic behavior and the adaptive patterns of early hominids and then considering the potential effects of varying intensities of information exchange on the functioning of the systems. This second approach should contribute to an understanding of the selection pressures that have moulded the evolution of language abilities. PART 1 of this paper follows the first approach, and PART I I the second.

Archeological Traces of Early Hominid Activities, East of Lake Rudolf, Kenya

Excavations have demonstrated that stone artifacts occur stratified within beds of Lower Pleistocene (or end Pliocene) age. At one site a low-density scatter of worked stone objects occurs together with small but significant quantities of broken-up bones. Potassium-argon dates indicate an age greater than 2 million years; thus, this may be the oldest known hominid occupation site. More than 20 hominid fossils have been recovered from various sedimentary formations in the area.

The Karari Industry: Early Pleistocene archaeological evidence from the terrain east of Lake Turkana, Kenya

Information concerning the technology, land-use patterns and activities of early hominids is being recovered from the Upper Member of the Koobi Fora Formation. The term Karari Industry is proposed for a distinctive local series of artefact assemblages that date to the period between 1.2 and 1.6 Myr BP.