A Spring Forward for Hominin Evolution in East Africa

Abstract

Groundwater is essential to modern human survival during drought periods. There is also growing geological evidence of springs associated with stone tools and hominin fossils in the East African Rift System (EARS) during a critical period for hominin evolution (from 1.8 Ma). However it is not known how vulnerable these springs may have been to climate variability and whether groundwater availability may have played a part in human evolution. Recent interdisciplinary research at Olduvai Gorge, Tanzania, has documented climate fluctuations attributable to astronomic forcing and the presence of paleosprings directly associated with archaeological sites. Using palaeogeological reconstruction and groundwater modelling of the Olduvai Gorge paleo-catchment, we show how spring discharge was likely linked to East African climate variability of annual to Milankovitch cycle timescales. Under decadal to centennial timescales, spring flow would have been relatively invariant providing good water resource resilience through long droughts. For multi-millennial periods, modelled spring flows lag groundwater recharge by 100 s to 1000 years. The lag creates long buffer periods allowing hominins to adapt to new habitats as potable surface water from rivers or lakes became increasingly scarce. Localised groundwater systems are likely to have been widespread within the EARS providing refugia and intense competition during dry periods, thus being an important factor in natural selection and evolution, as well as a vital resource during hominin dispersal within and out of Africa.

Testing Dietary Hypotheses of East African Hominines Using Buccal Dental Microwear Data

“…Moreover, there are concerns about the viability of a diet specialized in freshwater resources. Ancient hominin species lived near freshwater springs, rivers, lakes or estuaries [133–137], which has led several authors to speculate that access to freshwater from endorheic lakes of the East African Rift System (EARS) would have been vital for hominin survival and expansion during the Pliocene [134,138–140]. However, many of these lakes would have been saline during the Pliocene [140,141].…”

“…It may seem unlikely that P . boisei would have been a crab-specialist in a highly dispersed resource landscape if the productivity of the freshwater lakes would not have been sufficient to maintain the large populations of crabs needed to feed a highly specialized crab-consuming hominin [133]. However, consumption of fresh water crabs might have been a sporadic, or even a fallback resource for the paranthropines.…”

Modelling the role of groundwater hydro-refugia in East African hominin evolution and dispersal

“…The only way of directly testing the model validity over much longer timescales is through geological evidence, and output from an identical analytical model has previously been shown to be consistent with the geological record at Olduvai Gorge, Tanzania within the study area22. However, another approach is to compare the analytical model used here with a more complex numerical model simulation operating over longer timescales, as a proxy for actual data.…”

Subtle signatures of seeps: Record of groundwater in a Dryland, DK, Olduvai Gorge, Tanzania

“…Rift‐related extensional tectonics segmented the Olduvai stratigraphy into blocks separated mainly by normal faults (Hay, ). Similar to other rift basin localities: Mesozoic, eastern North American rift basins (Birney de Wet & Hubert, ; de Wet et al ., ) and Plio‐Pleistocene, southern Rio Grande Rift, USA (Mack et al ., ), bedrock, faults, and magmatic sources influence groundwater composition and flow patterns at Olduvai (Ashley & Hay, ; Cuthbert & Ashley, ).…”

“…Today groundwater exits at the base of the slope creating a lake/swamp called Obalbal. The scenario was probably similar during the Pleistocene, at which time the Ngorongoro Highland was even higher (Cuthbert & Ashley, ). This scenario is, apparently, a common scenario along the EARS as Olago et al .…”