TY - JOUR A1 - Trauth, Martin H. A1 - Bergner, Andreas G. N. A1 - Foerster, Verena A1 - Junginger, Annett A1 - Maslin, Mark A. A1 - Schäbitz, Frank T1 - Episodes of environmental stability versus instability in Late Cenozoic lake records of Eastern Africa JF - Journal of human evolution N2 - Episodes of environmental stability and instability may be equally important for African hominin speciation, dispersal, and cultural innovation. Three examples of a change from stable to unstable environmental conditions are presented on three different time scales: (1) the Mid Holocene (MH) wet dry transition in the Chew Bahir basin (Southern Ethiopian Rift; between 11 ka and 4 ka), (2) the MIS 5-4 transition in the Naivasha basin (Central Kenya Rift; between 160 ka and 50 ka), and (3) the Early Mid Pleistocene Transition (EMPT) in the Olorgesailie basin (Southern Kenya Rift; between 1.25 Ma and 0.4 Ma). A probabilistic age modeling technique is used to determine the timing of these transitions, taking into account possible abrupt changes in the sedimentation rate including episodes of no deposition (hiatuses). Interestingly, the stable-unstable conditions identified in the three records are always associated with an orbitally-induced decrease of insolation: the descending portion of the 800 kyr cycle during the EMPT, declining eccentricity after the 115 ka maximum at the MIS 5-4 transition, and after similar to 10 ka. This observation contributes to an evidence-based discussion of the possible mechanisms causing the switching between environmental stability and instability in Eastern Africa at three different orbital time scales (10,000 to 1,000,000 years) during the Cenozoic. This in turn may lead to great insights into the environmental changes occurring at the same time as hominin speciation, brain expansion, dispersal out of Africa, and cultural innovations and may provide key evidence to build new hypotheses regarding the causes of early human evolution. (C) 2015 Elsevier Ltd. All rights reserved. KW - Paleoclimate KW - East Africa KW - Human evolution KW - Lakes KW - Sediments Y1 - 2015 U6 - https://doi.org/10.1016/j.jhevol.2015.03.011 SN - 0047-2484 VL - 87 SP - 21 EP - 31 PB - Elsevier CY - London ER - TY - JOUR A1 - Maslin, Mark A. A1 - Shultz, Susanne A1 - Trauth, Martin H. T1 - A synthesis of the theories and concepts of early human evolution JF - Philosophical transactions of the Royal Society of London : B, Biological sciences N2 - Current evidence suggests that many of the major events in hominin evolution occurred in East Africa. Hence, over the past two decades, there has been intensive work undertaken to understand African palaeoclimate and tectonics in order to put together a coherent picture of how the environment of Africa has varied over the past 10 Myr. A new consensus is emerging that suggests the unusual geology and climate of East Africa created a complex, environmentally very variable setting. This new understanding of East African climate has led to the pulsed climate variability hypothesis that suggests the long-term drying trend in East Africa was punctuated by episodes of short alternating periods of extreme humidity and aridity which may have driven hominin speciation, encephalization and dispersals out of Africa. This hypothesis is unique as it provides a conceptual framework within which other evolutionary theories can be examined: first, at macro-scale comparing phylogenetic gradualism and punctuated equilibrium; second, at a more focused level of human evolution comparing allopatric speciation, aridity hypothesis, turnover pulse hypothesis, variability selection hypothesis, Red Queen hypothesis and sympatric speciation based on sexual selection. It is proposed that each one of these mechanisms may have been acting on hominins during these short periods of climate variability, which then produce a range of different traits that led to the emergence of new species. In the case of Homo erectus (sensu lato), it is not just brain size that changes but life history (shortened inter-birth intervals, delayed development), body size and dimorphism, shoulder morphology to allow thrown projectiles, adaptation to long-distance running, ecological flexibility and social behaviour. The future of evolutionary research should be to create evidence-based meta-narratives, which encompass multiple mechanisms that select for different traits leading ultimately to speciation. KW - human evolution KW - East Africa KW - palaeoclimatology KW - hominin KW - pulsed climate variability framework Y1 - 2015 U6 - https://doi.org/10.1098/rstb.2014.0064 SN - 0962-8436 SN - 1471-2970 VL - 370 IS - 1663 PB - Royal Society CY - London ER - TY - JOUR A1 - Maslin, Mark A. A1 - Brierley, Chris M. A1 - Milner, Alice M. A1 - Shultz, Susanne A1 - Trauth, Martin H. A1 - Wilson, Katy E. T1 - East African climate pulses and early human evolution JF - Quaternary science reviews : the international multidisciplinary research and review journal N2 - Current evidence suggests that all of the major events in hominin evolution have occurred in East Africa. Over the last two decades, there has been intensive work undertaken to understand African palaeoclimate and tectonics in order to put together a coherent picture of how the environment of East Africa has varied in the past. The landscape of East Africa has altered dramatically over the last 10 million years. It has changed from a relatively flat, homogenous region covered with mixed tropical forest, to a varied and heterogeneous environment, with mountains over 4 km high and vegetation ranging from desert to cloud forest. The progressive rifting of East Africa has also generated numerous lake basins, which are highly sensitive to changes in the local precipitation-evaporation regime. There is now evidence that the presence of precession-driven, ephemeral deep-water lakes in East Africa were concurrent with major events in hominin evolution. It seems the unusual geology and climate of East Africa created periods of highly variable local climate, which, it has been suggested could have driven hominin speciation, encephalisation and dispersal out of Africa. One example is the significant hominin speciation and brain expansion event at -1.8 Ma that seems to have been coeval with the occurrence of highly variable, extensive, deep-water lakes. This complex, climatically very variable setting inspired first the variability selection hypothesis, which was then the basis for the pulsed climate variability hypothesis. The newer of the two suggests that the long-term drying trend in East Africa was punctuated by episodes of short, alternating periods of extreme humidity and aridity. Both hypotheses, together with other key theories of climate-evolution linkages, are discussed in this paper. Though useful the actual evolution mechanisms, which led to early hominins are still unclear and continue to be debated. However, it is clear that an understanding of East African lakes and their palaeoclimate history is required to understand the context within which humans evolved and eventually left East Africa. (C) 2014 The Authors. Published by Elsevier Ltd. KW - Human evolution KW - East Africa KW - Palaeoclimatology KW - Palaeoliminology KW - Tectonics KW - Hominin KW - Orbital forcing KW - Cenozoic climate transitions KW - Pulsed climate variability hypothesis Y1 - 2014 U6 - https://doi.org/10.1016/j.quascirev.2014.06.012 SN - 0277-3791 VL - 101 SP - 1 EP - 17 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Fer, Istem A1 - Tietjen, Britta A1 - Jeltsch, Florian A1 - Trauth, Martin H. T1 - Modelling vegetation change during Late Cenozoic uplift of the East African plateaus JF - Palaeogeography, palaeoclimatology, palaeoecology : an international journal for the geo-sciences N2 - The present-day vegetation in the tropics is mainly characterized by forests worldwide except in tropical East Africa, where forests only occur as patches at the coast and in the uplands. These forest patches result from the peculiar aridity that is linked to the uplift of the region during the Late Cenozoic. The Late Cenozoic vegetation history of East Africa is of particular interest as it has set the scene for the contemporary events in mammal and hominin evolution. In this study, we investigate the conditions under which these forest patches could have been connected, and a previous continuous forest belt could have extended and fragmented. We apply a dynamic vegetation model with a set of climatic scenarios in which we systematically alter the present-day environmental conditions such that they would be more favourable for a continuous forest belt in tropical East Africa. We consider varying environmental factors, namely temperature, precipitation and atmospheric CO2 concentrations. Our results show that all of these variables play a significant role in supporting the forest biomes and a continuous forest belt could have occurred under certain combinations of these settings. With our current knowledge of the palaeoenvironmental history of East Africa, it is likely that the region hosted these conditions during the Late Cenozoic. Recent improvements on environmental hypotheses of hominin evolution highlight the role of periods of short and extreme climate variability during the Late Cenozoic specific to East Africa in driving evolution. Our results elucidate how the forest biomes of East Africa can appear and disappear under fluctuating environmental conditions and demonstrate how this climate variability might be recognized on the biosphere level. KW - Dynamic vegetation models KW - Palaeovegetation KW - Evolution KW - Late Cenozoic KW - East Africa KW - Climate change Y1 - 2016 U6 - https://doi.org/10.1016/j.palaeo.2016.04.007 SN - 0031-0182 SN - 1872-616X VL - 467 SP - 120 EP - 130 PB - Elsevier CY - Amsterdam ER -