The ecology of dispersal in early Homo species

Dispersal is one of the most fascinating processes in human evolutionary history. This complex process is directly connected to ecological, climatic, and environmental changes affecting animal communities and humans as its indivisible part. By itself species are responding to the changes differently, and their survival depends on the strategy species choose, expressed in the niche breadth and its demography. Inspired by the fact that humans are and always have been part of the nature, I propose a paleontropological and ecological integrated scenario and aim at understanding the environmental/ecosystem dynamics of Homo species dispersal out of Africa into Eurasia. The dispersal of humans was spurred by both intrinsic population factors (demography) and by climatic/environmental conditioning(biogeographic barriers, unsuitable climates). Yet, within any given community competitive relationships and species interaction in general affect species liability to survive the change. Species over evolutionary times, either adapts to the change, disperse into favourable territories where the environmental conditions are suitable as their former habitats, or worse become extinct. It is currently believed that the presence of humans didn’t have profound effects on the herbivore populations until very recently (Pushkina and Raia, 2008). This may be well true because dense herbivore populations are not controlled by predation. Conversely, humans had a strong influence on the distribution of carnivores, either by interference of competitive exclusion (Pushkina and Raia, 2008). Around 2 million years ago, when Homo first arose, the relationship between humans and carnivores begun to change, slowly at the beginning but much faster later, humans changed their strategy to earn food, from occasional scavenging towards full predatory activity (Hladik and Pasquet, 2002). The initial stasis but eventually the exponential increase in morphology, and the quality and technology of tool implements seems to borne this out. This process passed through strong environmental/climatic changes and faunal turnovers, and intermingles with major migrations and speciation events. On such changes humans were reacting in several ways, either by demographical or cultural shifts displayed by niche breadth and environmental preferences deviations. My main goal is to examine human dispersals ecology from a paleogeographical perspective, to evaluate the effects of competitive relationships (influence of humans on carnivores and vice versa), and the influence of environmental (climatic) changes on their populations and distributions. Modern evolutionary sciences about human evolution and dispersal are plenty of controversies. Evidence of early Pleistocene hominid dispersal outside Africa is scant and still object of debate. Before discoveries of earliest Eurasian Pleistocene sites, most of the early evidences appeared to support a relatively late initial dispersal after around 1 Ma, suggesting 6 Acheulean technological innovation as decisive aspect. Thanks to discoveries of Dmanisi (Lordkipanidze et al. 2013) and Chinese (Zhu, 2008) sites today it is suggested that the first dispersal happened around 1.9 Ma. If that evidence is correct, such an early dispersal may be better envisioned as driven more strongly by biological and ecological factors (Shipman at al. 1989; Anton et al. 2002) than by technological breakthroughs (Gabunia at al. 2002). Now there is general agreement that Homo erectus evolved in Africa, and then spread to Eurasia (Templeton, 2002). First dispersals of this species were accompanied by well-known climatic-environmental (faunal) changes (deMenocal, 2004; Norton and Braun, 2010; O'Regan, 2011). Although paleoanthropologists generally agree that modern humans evolved from Homo erectus, they disagree in their interpretations of the evolutionary mechanisms that controlled the human lineage evolutionary process. Two decades ago these interpretations were based on limited information and often emphasized on unique fossil discoveries, missing the support of natural sciences, but the growing body of multidistiplinary research gave a possibility to produce several evolutionary models, explaining the origins of modern Homo sapiens. Following two main opposing models such are “Recent African Origin” and “Multiregional Evolution” appeared other two models “Hybridization and Replacement model” and “Assimilation Model” (Strienger, 2002). In contrast of Multiregionalism (Fryer 1993), which denies existence of any particular region as a cradle of human origins (Thorne and Wolpoff, 1992), more balanced "Recent African Origin", which is slightly different from so called "splitter" views (Tattersal and Schwartz, 2008), proposes that a second wave of human dispersal out of Africa happened around 1 Ma, the new human species known as Homo heidelbergensis gave rise to Homo neanderthalensis in Eurasia, and Homo sapiens in Africa (Stringer, 2002; Rightmire, 2008), this event also was accompanied by major climatic-environmental turnovers. Finally, modern humans originated in Africa crowned dispersal about 100 Ka from where they spread around the world and replaced aboriginal archaic human populations in other areas of Eurasia by little hybridization with these groups. Ultimate genetic studies during the past ten years were very successful for genetic sciences; amazing discoveries were made in modern human origin studies. Extracted hominine DNA sequences demonstrated and proved fossil record-based presumptions (Trinkaus 2007; Smith, 2011) about genetic flow and admixture between Neanderthals and modern humans (Green et al., 2010; Trinkaus, 2005; Rak, 1998;). That information is reflected in "Hybridization and Replacement" model as a variant of the recent African origin model. It is based on the same fundament, but uses more of hybridization between the migrating population and the indigenous pre-modern populations (Bräuer et al., 2004) in turn "Assimilation Model" with multiregional approach recognizes African origin of modern humans (Smith, 1992), but refuses population dispersal, as a major factor in the origins of modern humans, emphasized the importance of gene flow resulting phenotypic change (Aiello, 1993). After processing information the methodological structure of the research was constructed, 7 the aim is fourfold: Hypothesis creation, definition of variables, database formation, and statistical analysis. First I proposed several basic hypotheses associated with dispersal of Pleistocene humans and its accompanying environmental-climatic changes. The hypotheses were divided in time and the space, and in terms of ecology gradually described the steps of human lineage evolutionary history. As a following step in research were involved several fauna-related ecological variables as are: climatic variables reconstructed by taxon-free (Damuth, 1992) ecomophological variables (herbivores teeth crown characters: Hypsodonty, Loph) (Liu et al. 2013; Eronen, 2010), presence/absence of faunal entities and incorporated them with geographical and time-related variables. I formed database encompassing whole this information using online accessible databases, which were controlled trough the scientific literature and then we opted several statistical and geostatistical analysis as are: simple and multivariate Generalized linear models (GLM), bootstrap resampling, principal component analysis (PCA), geostatistical interpolation method of Kriging, Least-cost path and rout calculation and species distribution modeling (SDM), via R (Cran) software. Finally, I will interpret these long-term characteristics for each dispersal event, estimate the effect of humans on the fauna through time and vice versa, and identify corridors of human dispersal, and their coincidence with moments of climatic change.