Paper short abstract:

In many ways it is unsurprising that human evolution occurred in East Africa because of the huge changes that have occurred in the local environment. On the long-term these include major tectonics event and global climate changes. On the short time scale wet-dry cycles are driven by orbital forcing.

Paper long abstract:

In many ways it is unsurprising that human evolution occurred in East Africa because of the huge changes that have occurred in the local environment. Long-term changes in the African environment have been influenced by the birth of the Sahara desert, re-evolution of C4 plants, Messinian Salinity Crisis, uplift and rifting of East Africa, start of Northern Hemisphere glaciation, Development of the Walker circulation and Mid-Pleistocene transition. On shorter time scales African climate is profoundly altered by orbital forcing. Every 400,000 years there are distinct periods when the climate of East Africa cycles between extremely wetness when the whole of the Rift valley was full of deep freshwater lakes to hyper-arid conditions when huge amounts of dust were blown into the surrounding oceans. This extreme climate variability varies on a 20,000 years frequency and suggests that precession is forcing the local climate to switch between extremely wet and dry phases. These periods of highly variable climate seem to only last 100,000 years. In between there are long periods of time when there seems to very little change in East Africa climate and no lakes apart from the large permanent ones such as Lake Turkana. These short periods of extreme climate variability seem to correlate to key periods of hominin evolution; such as the appearance of A. ramidus, the first appearance of Homo and Paranthropus genus, the first appearance of P. robustus H. erectus and H. ergaster, the first appearance of H. heidelbergensis and the first appearance of H. sapiens.

Paper short abstract:

In this paper we use case studies from eastern and southern Plio-Pleistocene Africa to consider how palaeoecological evidence from different scales is used to reconstruct human biological and technological evolution.

Paper long abstract:

Hominin ecology and behaviour is interpreted within a complex and often poorly resolved aggregation of data that includes records of large-scale global climate shifts, regional floral and faunal records, and highly localised records of, for example, sedimentology and pedology. Palaeoanthropologists ask a range of questions, on different geographical levels, so reconstructing the settings for human evolution and behaviour at an appropriate level requires understanding of the scope and scale of palaeoenvironmental data and methods, as well as conceptual and analytical tools to merge data at different scales when required. In this paper, we use examples and case studies from Plio-Pleistocene eastern and southern Africa to explore issues of palaeoecological scope and scale, and consider how studies acting at different scales may provide varying perspectives on the patterns and processes of human biological and technological evolution.

Paper short abstract:

The sediments at Olduvai Gorge, Tanzania, record evidence of hominin exploitation throughout the stratigraphy. Carbonate deposits associated with land surfaces provide a useful resource for investigating palaeohydrology at times of hominin activity, and the potential drivers for hominin utilisation.

Paper long abstract:

The sediments at Olduvai Gorge, Tanzania record multiple palaeo-land surfaces with evidence of significant hominin evolution and cultural change during the Pleistocene. Subsurface carbonate deposits are associated with these land surfaces, whose crystal textures and geochemistry were determined by processes operating during their formation and subsequent diagenetic alteration. Using these characteristics the carbonates have been grouped into palaeoenvironmental types; vadose zone, phreatic zone, capillary zone, evaporitic zone; and the sources of water during their formation can be inferred. The carbonates, when located within tightly constrained geographical and stratigraphic contexts, correlated using tuffs and lake-parasequences, can be used as a palaeohydrological proxy to identify distinct wetting and drying trends through different time intervals and up to very high sub-Milankovitch frequencies. Consequently they provide an effective method for understanding the wider palaeohydrology at land surfaces and the factors influencing potential hominin resource exploitation at favoured locations. New core from three locations at Olduvai have revealed multiple previously unrecorded soil sequences with carbonate horizons. The soil development identifies surfaces with prolonged exposure in locations previously thought to have had much more limited exposure times. Using the methodology developed in earlier studies, these carbonates can be used as useful indicators of the palaeohydrological and thus palaeoclimatic conditions and potential sources of water in a location much closer to the central palaeolake basin than had been previously predicted.

Paper short abstract:

Measurement of East African palaeoclimatic variation has concentrated on drying/wetting cycles of Milankovitch band. We explore higher frequency lake advance/withdrawal cycles on millenial scales, helping to identify palaeo-land surfaces, and allowing highly resolved correlation with lake drillcores.

Paper long abstract:

Measurements of East African palaeoclimatic variation have so far concentrated on drying/wetting trends of the Milankovitch spectrum (>23,000a). However very high frequency (multimillenial) sub-Milankovitch cycles of lake flooding have been identified at Olduvai Gorge and have been termed Lake-parasequences, analogous to marine parasequences of Milankovitch period. These have previously been applied to the high-resolution correlation of hominin assemblage levels, such as HWK E Level 1 and FLK Level 22. We use these high frequency lake cycles to demonstrate our ability to identify palaeo-land surfaces over wide areas and correlate between drillcores and sites of interest to human origins studies. Our current test interval to apply Sequence Stratigraphic concepts concerns the sections between the Bed I Basalt and Tuff IB, including Leakey's well-known "living floor" at DK. Derived from trench backwalls, a high-resolution trench- and outcrop-based stratigraphic framework defines successive land surfaces, allowing their correlation with recently drilled Borehole 2A, sited in an offshore lake setting. Bracketing this interval are the Bed I Basalt (1.877+0.013 Ma), prominent in core 2A, and Tuff IB (1.848+0.003 Ma), confirmed geochemically. Since there are no major tuffs in the core between these two units, the Sequence Stratigraphic methods were required to provide ties within. The full import of this technique comes with the challenge to relate hominin sites and transitional surfaces to predominantly lacustrine borehole core sediments. Whereas facies cannot be correlated easily, Lake-parasequences can. As a pilot study we have undertaken correlation of the DK assemblage surface, previously excavated by us, to Borehole 2A. [Additional authors N. Toth & K. Schick]

Paper short abstract:

We evaluate patterns of species turnover (1.4-4.2my) in Bovidae, Suidae and Cercopithicidae in the Koobi Fora region. Species richness in these taxa correlates with East African hominin diversity. Shifts in community composition over the period suggest shifts between open and more closed woodland habitat.

Paper long abstract:

The origin of Homo ~1.8my arguably represents the most fundamental shift in the evolution of modern humans as rapid changes occurred across the entire biology of our hominin ancestors. Body and brain size increased, life history became delayed, early Homo left East Africa to colonise Eurasia and there were minor revolutions in technology. Frustratingly, we have struggled to contextualise whether intrinsic or extrinsic evolutionary pressures drove these changes. We have recently argued that pulsed changes in the climate and geology of the East African Rift valley created novel ecological conditions that coincide with major events in hominin evolution. To further evidence the impact of extrinsic environmental forces, here we evaluate patterns of species turnover (1.4-4.2my) in three mammalian families: Bovidae, Suidae and Cercopithicidae in the Koobi Fora region. Species richness in these taxa correlates with East African hominin diversity. Shifts in community composition over the period suggest shifts between open and more closed woodland habitat. Moreover, both lake records and pedogenic carbonate data suggest highest species richness and turnover events are associated with pulsed shifts in climate. Together these data strongly suggest that major climatic changes in the East African Rift valley fundamentally changed the trajectory of hominin evolution.

Paper short abstract:

A number of studies have proposed causal links between African climate change and events within hominin evolution. Here I discuss a number of biases inherent to both palaeoclimate archives and the hominin fossil record which may limit our ability to test these hypotheses.

Paper long abstract:

In recent decades, a number of studies have compared Miocene to Pleistocene palaeoclimate records with various aspects of the hominin fossil record, including speciation, extinction and species diversity. When palaeoclimate and evolutionary events are temporally coincident, a causal relationship is often assumed, and hypotheses are put forward to explain the possible mechanisms for these relationships. However, different palaeoclimate archives can show distinct climate trends, resulting in a patchy understanding of African climate history. I will demonstrate this using examples of inter-annual to supra-orbital rainfall and vegetation proxies from southern and eastern Africa.

The hominin fossil record is notoriously incomplete, and this limits the degree to which events within hominin evolution can be meaningfully compared with palaeoclimate proxies. Using a compilation of hominin fossils and stratigraphic horizons, I will present confidence intervals for the stratigraphic ranges of each early hominin species. This analysis shows that the First and Last Appearance Datum (FAD and LAD) for each species has a typical uncertainty of about a million years. I will also show that hominin species diversity is governed by the number of fossil-bearing localities, and needs to be corrected for sampling bias prior to comparison with climate proxies. Although the hominin fossil record is gradually improving, it will take decades of new discoveries to see a significant improvement in the quality of the dataset. In the meantime, proxies for the hominin fossil record, such as bovids or stone tool industries, may provide more reliable and fruitful comparisons with temporally constrained climatic events.