Out of Afar: the first hominin migration? Long-term landscape changes in the Afar region and implications for hominin bipedalism

Tectonic and geomorphological processes in East Africa have long shaped the habitats and ecosystems within which hominins evolved, with the Afar Depression, created through rifting and plate reorganisation, a striking example of landscape isolation potentially shaping evolutionary opportunity. Yet climate change in Africa has traditionally been regarded as a key driver of behavioural adaptations, particularly hominin bipedalism. Here we outline a refugial scenario for bipedalism, a complementary approach that situates the evolution of hominin bipedalism within the tectonic and geomorphic evolution of the Afar region. Our reconstruction draws on Geographic Information System (GIS) assisted mapping of successive tectonic stages, providing a spatial framework for evaluating isolation, faunal migration, and the opening of dispersal corridors. We suggest that geological isolation, reduced faunal exchange, and lowered predation pressures created a refugium in which upright locomotor behaviours could emerge in concert with climatic fluctuations and ecological pressures. The dominance of rifts and cliffs in this tectonically active area may also have reinforced bipedal strategies that later proved evolutionarily advantageous. By about 4.2 Ma, the Main Ethiopian Rift (MER) corridor, established by ca. 5 Ma, enabled southward dispersal, coinciding with the earliest secure evidence for facultative bipedal hominins in the Turkana record. Their sudden emergence contrasts with earlier regional absences and may reflect the earliest documented hominin migration “out of Afar” and into wider Africa. By combining fossil distribution with GIS-based landscape history, we demonstrate how geomorphological isolation can be integrated with climate-driven models, highlighting this refugial scenario as a complementary perspective for explaining the earliest bipedalism in the Afar region.