Paleofloras, paleovegetation and human evolution

Abstract

This special issue is aimed at exploring the links between environmental changes and the patterns of biological and cultural evolution of hominins. Its conception arises from the relative imbalance between hominin fossil discoveries and knowledge about paleoenvironments associated with these findings. The collection includes both new records and empirical work, with emphasis on floristic and vegetation features, as their crucial role in shaping landscapes and habitat resources.Within an evolutionary framework, it is this focus that has attracted the interest of a number of scholars concerned with the postulation that selective pressures on Primates in favor of bipedalism could be related to the depletion of forests in eastern and central Africa and that in turn this was as a consequence of climatic changes after 6 Ma (Dart, 1925; Sockol et al., 2007). This postulation, so-called Savannah hypothesis, contends that mammalian evolution itself can be related to the spread of more open (C4) grasslands in East Africa after about 10 Ma (Sage, 2004; Feakins et al., 2013; Uno et al., 2016). The evolution of Poaceae during the Paleogene and its ecological success at the biome scale during the Neogene (Carrión, 2003; Willis and McElwain, 2013) can be therefore interpreted as historical contingencies (ss. Gould, 1989, 2002) for human evolution (Fig. 1). Cultural transitions are doubtlessly involved. The emergence of the Oldowan industry and the internal diversification of australopithecines took place within the context of increasing variability in climatic conditions after about 2.8 Ma (Bobe et al., 2002; deMenocal, 2004). The appearance of Homo erectus and the associated Acheulian industry in Africa was coeval with environmental variability changes after 1.8 Ma (deMenocal and Bloemendal, 1995; deMenocal, 2004). From amore paleogeographic perspective, the earliest expansions of Homo towards southern Africa and Asia seem synchronous with the extinction of Paranthropus and have been correlated to the climatic changes that provoked desertification within a large part of the savannah biome of the Rift Valley and the southern Africa highveld (Ségalen et al., 2004). In this scenario, the new discoverings of H. erectus in Shangchen, China, at 2.12 Ma (Zhu et al., 2018) must be now taken into account. Yet, the earliest dispersals from Africa of Homo sapiens have been interpreted as associated with dry spells (Scholz et al., 2007; deMenocal, 2008; Carto et al., 2008; Armitage et al., 2011; Lopez et al., 2016). Technological innovation may possibly be connected with environmental variability (Anton et al., 2014). Considering Eurasia, Kahlke et al. (2011) indicated that the tendency of human fossil and archeological sites to occur preferentially in areas with a high diversity of habitats and resources, including large river systems. These characteristics are especially visible between 1.7 and 1.3 Ma, when humans spread westward through the Mediterranean region, and subsequently northwards during the early Middle Pleistocene interglacials. These authors argued that stable environmental conditions would be correlated with low-risk application of proven subsistence strategies, while innovation would have been prompted by high rates of environmental change, such as during the Upper Pleistocene when the western Palearctic experienced its most unfavorable conditions. For a more recent period, Finlayson and Carrión (2007), after examining the distribution of Middle to Upper Paleolithic transitional industries across Europe from 45 to 30 ka, found sharp physiographical boundaries between different types of archeological sites, suggesting that these industries, made by both Neanderthals and anatomically modern humans (AMHs), were independent responses to rapid climatic changes. These stresses, experienced by human populations across the Palearctic, would have created a platform for innovation that, in the Late Pleistocene, involved trends towards light, portable and projectile technology, portable over long distances thereby reducing risk in an unpredictable environment. The vegetation and other features of the physical environment have been regarded trigger points in the evolution, adaptation and/or Review of Palaeobotany and Palynology 267 (2019) 32–38