Human Evolution

A Tale of Two Deltas: On the origin of Homo and Australopithecus in the Eastern Mediterranean Messinian Salinity Crisis and subsequent speciation explained by dispersal analysis.

ABSTRACT    The Last Common Ancestor of hominins and panins dates to 6-8 million years ago (mya) whereas the oldest hominin fossil, Australopithecus anamensis, is dated 4.2 mya. Older hominid fossils, such as Ardipithecus, are known but are dubiously ancestral to Homo. A 2-million-year gap in the fossil record is unaccounted for. We demonstrate that this gap can be explained by dispersal analysis. When First Appearance Data is analyzed by means of Skellam’s dispersal law, hominin origins are traceable backwards to the Eastern Mediterranean during the Messinian Salinity Crisis (5.96-5.33 mya) when the Mediterranean was a desiccated basin ~2000 m below sea level. The basin environment was intensely hot, a salt desert except where major rivers (e.g., the Nile) discharged freshwater forming delta oases. A second delta existed along the Levant Coast. We posit that over 600-thousand years of living in this hot deltaic environment, proto-hominins evolved specialized thermoregulatory adaptations — naked sweaty skin, subcutaneous fat — and adaptive sequelae such as upright posture, bipedalism, and right-handedness. At 5.33 mya the Strait of Gibraltar reopened, the Atlantic Ocean poured in, and the Mediterranean basin refilled in as little as 2 months. This event, the Zanclean Flood, drove an exodus of proto-Australopithecus up the Nile River south into Africa, and propelled proto-Homo east into the Levant then further east into Asia. Dispersing along rivers and shorelines, populations bifurcated where they met major river junctures or ocean coastlines, thereby initiating vicariant speciation. Regression revealed a direct linear relationship between time-in-travel and distance-traveled with R2 = .998 in accordance with Skellam’s Law of constant rate of dispersal. The paths of dispersal of Australopithecus into Africa reproduce the geographic speciation of A. anamensis, bahrelghazali, and africanus. Dispersal paths of Homo into Asia reproduce the temporal-geographic locations of H. luzonensis and floresiensis and locates Homo erectus evolution in the Indian Subcontinent. The appearance of habilis and erectus in East Africa involved dispersal across the Bab el-Mandeb strait of the Red Sea from Arabia-Asia. The absence of PTERV1 retrovirus from the human genome, although present in Pan and Gorilla, is explained by this proposed history of dispersal.

This is a forthcoming paper, expected to be published here in December 2025.