Oldest evidence of tool making hominins in a grassland-dominated ecosystem

New Oldowan locality Sare-Abururu (ca. 1.7 Ma) provides evidence of diverse hominin behaviors on the Homa Peninsula, Kenya

The Homa Peninsula, in southwestern Kenya, continues to yield insights into Oldowan hominin landscape behaviors. The Late Pliocene locality of Nyayanga (∼3-2.6 Ma) preserves some of the oldest Oldowan tools. At the Early Pleistocene locality of Kanjera South (∼2 Ma) toolmakers procured a diversity of raw materials from over 10 km away and strategically reduced them in a grassland-dominated ecosystem. Here, we report findings from Sare-Abururu, a younger (∼1.7 Ma) Oldowan locality approximately 12 km southeast of Kanjera South and 18 km east of Nyayanga. Sare-Abururu has yielded 1754 artifacts in relatively undisturbed low-energy silts and sands. Stable isotopic analysis of pedogenic carbonates suggests that hominin activities were carried out in a grassland-dominated setting with similar vegetation structure as documented at Kanjera South. The composition of a nearby paleo-conglomerate indicates that high-quality stone raw materials were locally abundant. Toolmakers at Sare-Abururu produced angular fragments from quartz pebbles, representing a considerable contrast to the strategies used to reduce high quality raw materials at Kanjera South. Although lithic reduction at Sare-Abururu was technologically simple, toolmakers proficiently produced cutting edges, made few mistakes and exhibited a mastery of platform management, demonstrating that expedient technical strategies do not necessarily indicate a lack of skill or suitable raw materials. Lithic procurement and reduction patterns on the Homa Peninsula appear to reflect variation in local resource contexts rather than large-scale evolutionary changes in mobility, energy budget, or toolmaker cognition.

Homo heterogenus: Variability in early Pleistocene Homo environments

To understand the ecological dominance of Homo sapiens, we need to investigate the origins of the plasticity that has enabled our colonization of the planet. We can approach this by exploring the variability of habitats to which different hominin populations have adapted over time. In this article, we draw upon and synthesize the current research on habitats of genus Homo during the early Pleistocene. We examined 121 published environmental reconstructions from 74 early Pleistocene sites or site phases to assess the balance of arguments in the research community. We found that, while grasslands and savannahs were prominent features of Homo habitats in the early Pleistocene, current research does not place early Pleistocene Homo, in any single environmental type, but in a wide variety of environments, ranging from open grasslands to forests. Our analysis also suggests that the first known dispersal of Homo out of Africa was accompanied by niche expansion.

Steps to individuality in biology and culture

Did human culture arise through an evolutionary transition in individuality (ETI)? To address this question, we examine the steps of biological ETIs to see how they could apply to the evolution of human culture. For concreteness, we illustrate the ETI stages using a well-studied example, the evolution of multicellularity in the volvocine algae. We then consider how those stages could apply to a cultural transition involving integrated groups of cultural traditions and the hominins that create and transmit traditions. We focus primarily on the early Pleistocene and examine hominin carnivory and the cultural change from Oldowan to Acheulean technology. We use Pan behaviour as an outgroup comparison. We summarize the important similarities and differences we find between ETI stages in the biological and cultural realms. As we are not cultural anthropologists, we may overlook or be mistaken in the processes we associate with each step. We hope that by clearly describing these steps to individuality and illustrating them with cultural principles and processes, other researchers may build upon our initial exercise. Our analysis supports the hypothesis that human culture has undergone an ETI beginning with a Pan-like ancestor, continuing during the Pleistocene, and culminating in modern human culture. This article is part of the theme issue 'Human socio-cultural evolution in light of evolutionary transitions'.

Seasonality and Oldowan behavioral variability in East Africa

The extent, nature, and temporality of early hominin food procurement strategies have been subject to extensive debate. In this article, we examine evidence for the seasonal scheduling of resource procurement and technological investment in the Oldowan, starting with an evaluation of the seasonal signature of underground storage organs, freshwater resources, and terrestrial animal resources in extant primates and modern human hunter-gatherer populations. Subsequently, we use the mortality profiles, taxonomic composition, and taphonomy of the bovid assemblages at Kanjera South (Homa Peninsula, Kenya) and FLK-Zinj (Olduvai Gorge, Tanzania) to illustrate the behavioral flexibility of Oldowan hominins, who were targeting different seasonally vulnerable demographics. In terms of the lithic assemblages, the specific opportunities and constraints afforded by dry season subsistence at FLK-Zinj may have disincentivized lithic investment, resulting in a more expedient toolkit for fast and effective carcass processing. This may have been reinforced by raw material site provisioning during a relatively prolonged seasonal occupation, reducing pressures on the reduction and curation of lithic implements. In contrast, wet season plant abundance would have offered a predictable set of high-quality resources associated with low levels of competition and reduced search times, in the context of perhaps greater seasonal mobility and consequently shorter occupations. These factors appear to have fostered technological investment to reduce resource handling costs at Kanjera South, facilitated by more consistent net returns and enhanced planning of lithic deployment throughout the landscape. We subsequently discuss the seasonality of freshwater resources in Oldowan procurement strategies, focusing on FwJj20 (Koobi Fora, Kenya). Although more analytical studies with representative sample sizes are needed, we argue that interassemblage differences evidence the ability of Oldowan hominins to adapt to seasonal constraints and opportunities in resource exploitation.

Ecological perspectives on technological diversity at Kanjera South

The aspects of hominin behavior responsible for Oldowan stone tool variation are the focus of much debate. There is some consensus that this variation arises from a combination of ecological and cultural factors. The diversity of raw material types and technological strategies present at Kanjera South, Kenya, provide an opportunity to examine the interacting influences of ecology and culture on Oldowan stone tool variation. Here, we combine previous analyses of raw material properties, provenance, and technology with quantitative measures of core reduction intensity and tool utilization to examine the influence of both ecological and technocultural factors on stone tool variation at Kanjera South. The results of this analysis reflect a dynamic relationship between raw material properties, provenance, and hominin mobility. Exotic raw materials are generally more resistant to edge attrition compared with those available locally, which may have incentivized their transport over long distances and more extensive reduction. Cores produced on raw materials from distant sources also exhibit more complex core reduction strategies than locally acquired materials. While this pattern is partially due to the differences in the quality of knappable stone, bifacial centripetal and multifacial core reduction strategies also arise due to the continuous transport and use of exotic raw materials. Moreover, the variation in stone tool reduction is not consistent with neutral models of stone tool transport and discard. These results demonstrate that ecological factors such as raw material provenance and physical properties have strong impacts on reduction intensity and the technological strategies used by hominins.

Earliest Olduvai hominins exploited unstable environments ~ 2 million years ago

Rapid environmental change is a catalyst for human evolution, driving dietary innovations, habitat diversification, and dispersal. However, there is a dearth of information to assess hominin adaptions to changing physiography during key evolutionary stages such as the early Pleistocene. Here we report a multiproxy dataset from Ewass Oldupa, in the Western Plio-Pleistocene rift basin of Olduvai Gorge (now Oldupai), Tanzania, to address this lacuna and offer an ecological perspective on human adaptability two million years ago. Oldupai's earliest hominins sequentially inhabited the floodplains of sinuous channels, then river-influenced contexts, which now comprises the oldest palaeolake setting documented regionally. Early Oldowan tools reveal a homogenous technology to utilise diverse, rapidly changing environments that ranged from fern meadows to woodland mosaics, naturally burned landscapes, to lakeside woodland/palm groves as well as hyper-xeric steppes. Hominins periodically used emerging landscapes and disturbance biomes multiple times over 235,000 years, thus predating by more than 180,000 years the earliest known hominins and Oldowan industries from the Eastern side of the basin.

Soil and plant phytoliths from the Acacia-Commiphora mosaics at Oldupai Gorge (Tanzania)

This article studies soil and plant phytoliths from the Eastern Serengeti Plains, specifically the Acacia-Commiphora mosaics from Oldupai Gorge, Tanzania, as present-day analogue for the environment that was contemporaneous with the emergence of the genus Homo. We investigate whether phytolith assemblages from recent soil surfaces reflect plant community structure and composition with fidelity. The materials included 35 topsoil samples and 29 plant species (20 genera, 15 families). Phytoliths were extracted from both soil and botanical samples. Quantification aimed at discovering relationships amongst the soil and plant phytoliths relative distributions through Chi-square independence tests, establishing the statistical significance of the relationship between categorical variables within the two populations. Soil assemblages form a spectrum, or cohort of co-ocurring phytolith classes, that will allow identifying environments similar to those in the Acacia-Commiphora ecozone in the fossil record.

Social evolution in Plio-Pleistocene hominins: Insights from hamadryas baboons and paleoecology

Reconstructions of hominin evolution have long benefited from comparisons with nonhuman primates, especially baboons and chimpanzees. The hamadryas baboon (Papio hamadryas) is arguably one of the best such models, as it exhibits both the male kin bonding and the cross-sex pair bonding thought to have been important in hominin evolution. Here we link processes of behavioral evolution in hamadryas baboons with those in a Plio-Pleistocene hominin, provisionally identified as Homo erectus (sensu lato) - a pivotal species in that its larger body and brain size and wider ranging patterns increased female costs of reproduction, increasing the importance of sociality. The combination of these higher costs of reproduction and shifts in diet and food acquisition have previously been argued to have been alleviated either via strengthening of male-female bonds (involving male provisioning and the evolution of monogamy) or via the assistance of older, post-reproductive females (leading to post-reproductive longevity in females, i.e., the grandmother hypothesis). We suggest that both arrangements could have been present in Plio-Pleistocene hominins if they lived in multilevel societies. Here we expand on our earlier scenario with two sets of recent data in support of it, (1) archaeological data from the 2 million year old Oldowan site of Kanjera South, Kenya and other sites that are suggestive of tool dependent foraging on nutrient dense resources (animal carcasses and plant underground storage organs), cooperation, and food sharing; and (2) a pattern of genetic variation in hamadryas baboons that suggests the operation of kin selection among both males and females at multiple levels of society. Taken together, these two sets of data strengthen our model and support the idea of a complex society linked by male-male, male-female, and female-female bonds at multiple levels of social organization in Plio-Pleistocene hominins.

Shifting Climates, Foods, and Diseases: The Human Microbiome through Evolution

Human evolution has been punctuated by climate anomalies, structuring environments, deadly infections, and altering landscapes. How well humans adapted to these new circumstances had direct effects on fitness and survival. Here, how the gut microbiome could have contributed to human evolutionary success through contributions to host nutritional buffering and infectious disease resistance is reviewed. How changes in human genetics, diet, disease exposure, and social environments almost certainly altered microbial community composition is also explored. Emerging research points to the microbiome as a key player in host responses to environmental change. Therefore, the reciprocal interactions between humans and their microbes are likely to have shaped human patterns of local adaptation throughout our shared evolutionary history. Recent alterations in human lifestyle, however, are altering human microbiomes in unprecedented ways. The consequences of interrupted host-microbe relationships for human adaptive potential in the future are unknown.

Plio-Pleistocene decline of African megaherbivores: No evidence for ancient hominin impacts

It has long been proposed that pre-modern hominin impacts drove extinctions and shaped the evolutionary history of Africa's exceptionally diverse large mammal communities, but this hypothesis has yet to be rigorously tested. We analyzed eastern African herbivore communities spanning the past 7 million years-encompassing the entirety of hominin evolutionary history-to test the hypothesis that top-down impacts of tool-bearing, meat-eating hominins contributed to the demise of megaherbivores prior to the emergence of Homo sapiens We document a steady, long-term decline of megaherbivores beginning ~4.6 million years ago, long before the appearance of hominin species capable of exerting top-down control of large mammal communities and predating evidence for hominin interactions with megaherbivore prey. Expansion of C₄ grasslands can account for the loss of megaherbivore diversity.

The meta-group social network of early humans: A temporal-spatial assessment of group size at FLK Zinj (Olduvai Gorge, Tanzania)

Humans are the only primates that maintain regular inter-group relationships and meta-group social networks that enable the inter-group flow of individuals. This is the basis of the band/tribe concept in the anthropology of modern foragers. The present work is a theoretical approach to the development of analytical tools to understand group size and the temporal scale of site occupation in the archaeological record. We selected FLK Zinj as one of the oldest examples of a taphonomically-supported anthropogenic site in which both variables (group size and time) could be modelled using a combination of modern forager regression estimates from their camp sizes and estimates derived from the combined use of modern African foragers' meat consumption rates per day per capita during the dry season and minimum estimates of flesh yields provided by the carcass parts preserved at FLK Zinj. This approach provides the basis for a testable hypothesis which should be further tested in other Oldowan sites. An estimate of 18-28 individuals occupying FLK Zinj was made, which is similar to the estimated 16 individuals of one of the 1.5 Ma Ileret Homo erectus footprint trails. It also shows a similar proportional distribution to Dunbar's equations (group size to neocortex ratio) as documented in modern foragers, which suggest that most of the social network of H. erectus was in the meta-group level as is the case of modern foragers. Irrespective of the range of variation discussed for both variables (group size and length of time represented), it is argued that neither small estimates of time nor small group sizes can account for the formation of FLK Zinj.

Distance-decay effect in stone tool transport by wild chimpanzees

Stone tool transport leaves long-lasting behavioural evidence in the landscape. However, it remains unknown how large-scale patterns of stone distribution emerge through undirected, short-term transport behaviours. One of the longest studied groups of stone-tool-using primates are the chimpanzees of the Taï National Park in Ivory Coast, West Africa. Using hammerstones left behind at chimpanzee Panda nut-cracking sites, we tested for a distance-decay effect, in which the weight of material decreases with increasing distance from raw material sources. We found that this effect exists over a range of more than 2 km, despite the fact that observed, short-term tool transport does not appear to involve deliberate movements away from raw material sources. Tools from the millennia-old Noulo site in the Taï forest fit the same pattern. The fact that chimpanzees show both complex short-term behavioural planning, and yet produce a landscape-wide pattern over the long term, raises the question of whether similar processes operate within other stone-tool-using primates, including hominins. Where hominin landscapes have discrete material sources, a distance-decay effect, and increasing use of stone materials away from sources, the Taï chimpanzees provide a relevant analogy for understanding the formation of those landscapes.

Aridity and hominin environments

Aridification is often considered a major driver of long-term ecological change and hominin evolution in eastern Africa during the Plio-Pleistocene; however, this hypothesis remains inadequately tested owing to difficulties in reconstructing terrestrial paleoclimate. We present a revised aridity index for quantifying water deficit (WD) in terrestrial environments using tooth enamel δ¹⁸O values, and use this approach to address paleoaridity over the past 4.4 million years in eastern Africa. We find no long-term trend in WD, consistent with other terrestrial climate indicators in the Omo-Turkana Basin, and no relationship between paleoaridity and herbivore paleodiet structure among fossil collections meeting the criteria for WD estimation. Thus, we suggest that changes in the abundance of C₄ grass and grazing herbivores in eastern Africa during the Pliocene and Pleistocene may have been decoupled from aridity. As in modern African ecosystems, other factors, such as rainfall seasonality or ecological interactions among plants and mammals, may be important for understanding the evolution of C₄ grass- and grazer-dominated biomes.

The social organization of Homo ergaster: Inferences from anti-predator responses in extant primates

Patterns of primate socioecology have been used to suggest that the first truly savanna-dwelling hominin, Homo ergaster, lived in sizeable groups. Here, we revisit these estimates and infer additional features of the social organization of these early hominins based on anti-predator responses observed across the primate taxon. We first show that the effect of habitat on primate group size, composition, and sexual dimorphism is negligible after controlling for substrate use and phylogeny: terrestrial species live in larger groups with more and bigger males than arboreal taxa. We next hypothesize that groups can only survive in open habitats if males are able to engage in joint counter-attacks against the large carnivorans typical of such environments. To test this, we analyze reports on primate counter-attacks against known predators and find these are indeed disproportionately frequent in terrestrial taxa living in open habitats, sometimes even involving the use of tentative weapons. If we subsequently only examine the taxa that are particularly adept at this (chimpanzees and baboons), we find an effect of habitat type on group size: groups on the savanna are larger than those in the forest. We thus infer that H. ergaster lived in very large groups with many males that jointly defended the group against carnivorans, and argue that these counter-attacks will readily have turned into confrontational scavenging and cooperative hunting, allowing Homo to move into the niche of social carnivore. These two features (life in very large multi-male groups and a switch to persistent carnivory) shaped the evolution of our lineage to such an extent that the social organization of H. ergaster may already have contained many key elements characterizing modern day foragers: male bonding, incipient male-female friendships with food sharing, a tendency toward endogamy, and the presence of large communities that eventually turned into the ethno-linguistic units we can still recognize today.

Macromammalian faunas, biochronology and palaeoecology of the early Pleistocene Main Quarry hominin-bearing deposits of the Drimolen Palaeocave System, South Africa

The Drimolen Palaeocave System Main Quarry deposits (DMQ) are some of the most prolific hominin and primate-bearing deposits in the Fossil Hominids of South Africa UNESCO World Heritage Site. Discovered in the 1990s, excavations into the DMQ have yielded a demographically diverse sample of Paranthropus robustus (including DNH 7, the most complete cranium of the species recovered to date), early Homo, Papio hamadryas robinsoni and Cercopithecoides williamsi. Alongside the hominin and primate sample is a diverse macromammalian assemblage, but prior publications have only provided a provisional species list and an analysis of the carnivores recovered prior to 2008. Here we present the first description and analysis of the non-primate macromammalian faunas from the DMQ, including all 826 taxonomically identifiable specimens catalogued from over two decades of excavation. We also provide a biochronological interpretation of the DMQ deposits and an initial discussion of local palaeoecology based on taxon representation.The current DMQ assemblage consists of the remains of minimally 147 individuals from 9 Orders and 14 Families of mammals. The carnivore assemblage described here is even more diverse than established in prior publications, including the identification of Megantereon whitei, Lycyaenops silberbergi, and first evidence for the occurrence of Dinofelis cf. barlowi and Dinofelis aff. piveteaui within a single South African site deposit. The cetartiodactyl assemblage is dominated by bovids, with the specimen composition unique in the high recovery of horn cores and dominance of Antidorcas recki remains. Other cetartiodactyl and perissodactyl taxa are represented by few specimens, as are Hystrix and Procavia; the latter somewhat surprisingly so given their common occurrence at penecontemporaneous deposits in the region. Equally unusual (particularly given the size of the sample) is the identification of single specimens of giraffoid, elephantid and aardvark (Orycteropus cf. afer) that are rarely recovered from regional site deposits. Despite the diversity within the DMQ macromammalian faunas, there are few habitat- or biochronologically-sensitive species that provide specific ecologic or age boundaries for the deposits. Recovered species can only support the non-specific, mixed open-to-closed palaeohabitats around Drimolen that have been reconstructed for the other penecontemporaneous South African palaeokarst deposits. The identified Equus quagga ssp. specimens recovered from the floor of the current excavation (∾−4.5–5 m below datum) suggests that most, if not all the DMQ specimens, were deposited after 2.33 Ma. Simultaneously, the carnivore specimens (D. cf. barlowi, L. silberbergi) suggest earlier Pleistocene (pre- 2.0–1.8 Ma) to maximally 1.6 Ma deposition (D. aff. piveteaui) for most of the DMQ fossil assemblage.

Stable isotope paleoecology of Late Pleistocene Middle Stone Age humans from the Lake Victoria basin, Kenya

Paleoanthropologists have long argued that environmental pressures played a key role in human evolution. However, our understanding of how these pressures mediated the behavioral and biological diversity of early modern humans and their migration patterns within and out of Africa is limited by a lack of archaeological evidence associated with detailed paleoenvironmental data. Here, we present the first stable isotopic data from paleosols and fauna associated with Middle Stone Age (MSA) sites in East Africa. Late Pleistocene (∼100-45 ka, thousands of years ago) sediments on Rusinga and Mfangano Islands in eastern Lake Victoria (Kenya) preserve a taxonomically diverse, non-analog faunal community associated with MSA artifacts. We analyzed the stable carbon and oxygen isotope composition of paleosol carbonate and organic matter and fossil mammalian tooth enamel, including the first analyses for several extinct bovids such as Rusingoryx atopocranion, Damaliscus hypsodon, and an unnamed impala species. Both paleosol carbonate and organic matter data suggest that local habitats associated with human activities were primarily riverine woodland ecosystems. However, mammalian tooth enamel data indicate that most large-bodied mammals consumed a predominantly C4 diet, suggesting an extensive C4 grassland surrounding these riverine woodlands in the region at the time. These data are consistent with other lines of paleoenvironmental evidence that imply a substantially reduced Lake Victoria at this time, and demonstrate that C4 grasslands were significantly expanded into equatorial Africa compared with their present distribution, which could have facilitated dispersal of human populations and other biotic communities. Our results indicate that early populations of Homo sapiens from the Lake Victoria region exploited locally wooded and well-watered habitats within a larger grassland ecosystem.

Evolution of earlyHomo: An integrated biological perspective

Integration of evidence over the past decade has revised understandings about the major adaptations underlying the origin and early evolution of the genusHomo. Many features associated withHomo sapiens, including our large linear bodies, elongated hind limbs, large energy-expensive brains, reduced sexual dimorphism, increased carnivory, and unique life history traits, were once thought to have evolved near the origin of the genus in response to heightened aridity and open habitats in Africa. However, recent analyses of fossil, archaeological, and environmental data indicate that such traits did not arise as a single package. Instead, some arose substantially earlier and some later than previously thought. From ~2.5 to 1.5 million years ago, three lineages of earlyHomoevolved in a context of habitat instability and fragmentation on seasonal, intergenerational, and evolutionary time scales. These contexts gave a selective advantage to traits, such as dietary flexibility and larger body size, that facilitated survival in shifting environments.

Old stones' song: use-wear experiments and analysis of the Oldowan quartz and quartzite assemblage from Kanjera South (Kenya)

Evidence of Oldowan tools by ∼2.6 million years ago (Ma) may signal a major adaptive shift in hominin evolution. While tool-dependent butchery of large mammals was important by at least 2.0 Ma, the use of artifacts for tasks other than faunal processing has been difficult to diagnose. Here we report on use-wear analysis of ∼2.0 Ma quartz and quartzite artifacts from Kanjera South, Kenya. A use-wear framework that links processing of specific materials and tool motions to their resultant use-wear patterns was developed. A blind test was then carried out to assess and improve the efficacy of this experimental use-wear framework, which was then applied to the analysis of 62 Oldowan artifacts from Kanjera South. Use-wear on a total of 23 artifact edges was attributed to the processing of specific materials. Use-wear on seven edges (30%) was attributed to animal tissue processing, corroborating zooarchaeological evidence for butchery at the site. Use-wear on 16 edges (70%) was attributed to the processing of plant tissues, including wood, grit-covered plant tissues that we interpret as underground storage organs (USOs), and stems of grass or sedges. These results expand our knowledge of the suite of behaviours carried out in the vicinity of Kanjera South to include the processing of materials that would be 'invisible' using standard archaeological methods. Wood cutting and scraping may represent the production and/or maintenance of wooden tools. Use-wear related to USO processing extends the archaeological evidence for hominin acquisition and consumption of this resource by over 1.5 Ma. Cutting of grasses, sedges or reeds may be related to a subsistence task (e.g., grass seed harvesting, cutting out papyrus culm for consumption) and/or a non-subsistence related task (e.g., production of 'twine,' simple carrying devices, or bedding). These results highlight the adaptive significance of lithic technology for hominins at Kanjera.

Earliest archaeological evidence of persistent hominin carnivory

The emergence of lithic technology by ∼2.6 million years ago (Ma) is often interpreted as a correlate of increasingly recurrent hominin acquisition and consumption of animal remains. Associated faunal evidence, however, is poorly preserved prior to ∼1.8 Ma, limiting our understanding of early archaeological (Oldowan) hominin carnivory. Here, we detail three large well-preserved zooarchaeological assemblages from Kanjera South, Kenya. The assemblages date to ∼2.0 Ma, pre-dating all previously published archaeofaunas of appreciable size. At Kanjera, there is clear evidence that Oldowan hominins acquired and processed numerous, relatively complete, small ungulate carcasses. Moreover, they had at least occasional access to the fleshed remains of larger, wildebeest-sized animals. The overall record of hominin activities is consistent through the stratified sequence – spanning hundreds to thousands of years – and provides the earliest archaeological evidence of sustained hominin involvement with fleshed animal remains (i.e., persistent carnivory), a foraging adaptation central to many models of hominin evolution.

Woody cover and hominin environments in the past 6 million years

The role of African savannahs in the evolution of early hominins has been debated for nearly a century. Resolution of this issue has been hindered by difficulty in quantifying the fraction of woody cover in the fossil record. Here we show that the fraction of woody cover in tropical ecosystems can be quantified using stable carbon isotopes in soils. Furthermore, we use fossil soils from hominin sites in the Awash and Omo-Turkana basins in eastern Africa to reconstruct the fraction of woody cover since the Late Miocene epoch (about 7 million years ago). (13)C/(12)C ratio data from 1,300 palaeosols at or adjacent to hominin sites dating to at least 6 million years ago show that woody cover was predominantly less than ∼40% at most sites. These data point to the prevalence of open environments at the majority of hominin fossil sites in eastern Africa over the past 6 million years.

The Pleistocene archaeology and environments of the Wasiriya Beds, Rusinga Island, Kenya

Western Kenya is well known for abundant early Miocene hominoid fossils. However, the Wasiriya Beds of Rusinga Island, Kenya, preserve a Pleistocene sedimentary archive with radiocarbon age estimates of >33-45 ka that contains Middle Stone Age artifacts and abundant, well-preserved fossil fauna: a co-occurrence rare in eastern Africa, particularly in the region bounding Lake Victoria. Artifacts and fossils are associated with distal volcanic ash deposits that occur at multiple localities in the Wasiriya Beds, correlated on the basis of geochemical composition as determined by electron probe microanalysis. Sediment lithology and the fossil ungulates suggest a local fluvial system and associated riparian wooded habitat within a predominantly arid grassland setting that differs substantially from the modern environment, where local climate is strongly affected by moisture availability from Lake Victoria. In particular, the presence of oryx (Oryx gazella) and Grevy's zebra (Equus grevyi) suggest a pre-Last Glacial Maximum expansion of arid grasslands, an environmental reconstruction further supported by the presence of several extinct specialized grazers (Pelorovis antiquus, Megalotragus sp., and a small alcelaphine) that are unknown from Holocene deposits in eastern Africa. The combination of artifacts, a rich fossil fauna, and volcaniclastic sediments makes the Wasiriya Beds a key site for examining the Lake Victoria basin, a biogeographically important area for understanding the diversification and dispersal of Homo sapiens from Africa, whose pre-Last Glacial Maximum history remains poorly understood.