Lateral variations in whole-rock and clay geochemistry of basal Bed II claystones in Olduvai Gorge, Tanzania, reflect water quality differences across the Eastern Lacustrine Plain ∼1.75 myr ago. Bulk Ba/Sr and (Na2O+K2O+MgO)/Al2O3 range from 1.4 to 4.2 and from 0.7 to 1.4, respectively, and indicate leaching of lacustrine claystones beneath freshwater wetlands at times following lake retreat. Bulk MgO/Al2O3 (0.3–1.0) and molar Mg/Al (0.5–3.9) ratios of <0.2-μm clays reflect alteration of Mg-rich lacustrine clays. These indicators point to freshest conditions near Locality 43 of Hay (1976; HWK-East; Leakey, 1971), moderate conditions to the east (Locality 40-MCK), and high salinity and alkalinity to the west (Localities 85-VEK, 45-FLK).

Clay geochemistry and artifact abundances are well correlated (r=−0.67, p<0.005), suggesting a relationship between paleo-water quality and hominid paleoecology. This pattern is consistent with predictions of greatest artifact discard/loss around freshwater sources where scavanging opportunities were greatest for hominids. This quantifies a relationship between artifact density distribution and a paleoecological proxy over landscape scales for the first time in Early Stone Age archaeology. In contrast, fossil bone abundance is uncorrelated (r=0.14, p=0.6), reflecting more complex taphonomic processes. Quantitative tests of landscape-scale land-use models are important for understanding early hominid behavior and its evolution.

Distances of raw material transportation reflect how hominid groups gather and exchange information. Early hominids moved raw materials short distances, suggesting a home range size, social complexity and communication system similar to primates in equivalent environments. After about 1.0 million years ago there was a large increase in raw material transfer distances, possibly a result of the emergence of the ability to pool information by using a protolanguage. Another increase in raw material transfer occurred during the late Middle Stone Age in Africa (after about 130,000 years ago), suggesting the operation of exchange networks. Exchange networks require a communication system with syntax, the use of symbols in social contexts and the ability to express displacement, which are the features of human language. Taking the Neanderthals as a case study, biological evidence and the results of computer simulations of the evolution of language, I argue for a gradual rather than catastrophic emergence of language coinciding with the first evidence of exchange networks.