Climate-inferred distribution estimates of mid-to-late Pliocene hominins

During the mid-to-late Pliocene (ca. 4-3 Ma), several hominin species were present in central Sahel, eastern and southern Africa. The potential for the discovery of hominin remains from this interval is limited by the availability of exposed Pliocene deposits and the ability to investigate them. As a result, most discoveries have been made in the Afar region of Ethiopia and in the Lake Turkana basin, thus unveiling only a portion of Pliocene hominins' probable geographical presence. In this study we provide a continental view of geographic areas potentially accessible to these hominins. To do so, we estimate the climatic envelope suitable for mid-to-late Pliocene hominin presence, using the earth system model IPSL-CM5A and the Maxent habitat suitability algorithm. Our analysis reveals high habitat suitability for these hominin species in semi-arid regions where annual thermal amplitude and mean annual precipitation are moderate, mostly corresponding to tropical xerophytic shrublands. Our habitat model estimates geographically continuous, suitable climatic conditions for hominins between central Sahel and northeastern Africa, but not between eastern and southern Africa. This discontinuity suggests that southern African and eastern African hominins were separated by an environmental barrier that could only be crossed during particularly favourable periods or by undertaking long-range dispersal over climatically hostile habitats. Under climate conditions of northern hemisphere summer at perihelion this climatic barrier is not present. In contrast, the Turkana basin, the Laetoli region, and a large part of southern Africa remain suitable for all precession angles, suggesting that these areas may have functioned as refugia. The constant presence of these stable areas combined with the periodic establishment of corridors for dispersion can potentially explain hominin diversity in eastern Africa.