Humans Used Alternate Migration Route Out of Africa 80,000 Years Ago

By no means is climate change a new phenomenon – in fact, throughout its 4.6-billion-year long history, the Earth has undergone innumerable climatic patterns over thousands of years. A new study based out of Arabia has suggested that one of the routes that Homo sapiens took to exit Africa was through the desert Levant area towards western Asia and northern Arabia via Jordan. A wide array of abandoned hand tools has helped establish this fact.

A second flake, or hand tool, seen from three different angles, discovered in the Jordan Rift Valley. The flakes helped scientists date human migration. (University of Southampton)

Arresting Longstanding Beliefs: Another Way Out of Africa

Historians and researchers have held a longstanding belief that during periods of lower sea levels, H. sapiens used a southern route of migration, by crossing the Red Sea from the Horn of Africa to reach the southwestern Arabian region.

The new study published in Sciences Advances has found an alternate route through the Jordan Rift Valley, which featured a riverine and wetland area, offering an optimal pathway for migration out of Africa, before venturing deep into the regions of the Levant and Arabia. The researchers categorically oppose the notion that a single migratory wave out of Africa occurred 60,000 years ago, another long-held belief.

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Dr Mahmoud Abass (Shantou University) on left, Professor Paul Carling (University of Southampton) in center and Dr John Jansen (Czech Academy of Sciences) on right, in the field in Jordan Rift Valley. (University of Southampton)

In a press release, Paul Carling, Professor of Geomorphology at the University of Southampton, commented that:

“It’s long been thought that when the sea level was low, humans used a southern crossing, via the Red Sea from the horn of Africa, to get to southwestern Arabia. However, our study confirms there was a well-trodden passage to the north, across the only land-route from Africa to Eurasia.”

Researchers propose that early human migrations out of Africa likely involved the utilization of natural pathways within the eastern Sahara, the Nile River Valley, or the coastal regions of the western Red Sea. These early groups of hunter-gatherers would have followed the movement of animals and hunted for their sustenance as they crossed into the Sinai Peninsula, which served as a land bridge connecting Africa to the broader Asian continent.

For many of these migrating hunter-gatherers, the next destination on their journey would have been the southern part of the Jordan Rift Valley. This valley holds a strategic position, bordered by the Dead Sea to the north and the Gulf of Aqaba to the south.

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Map showing archaeological, paleoclimatological, and paleoenvironmental records from the Levant and Arabia mentioned in the study. he arrows indicate the suggested routes of human dispersals out of Africa. (Abbas, M et al. 2023 / Science Advances)

Fieldwork and Ground-Level Evidence: Across the Jordan Rift Valley and Plateau

The research team was from the University of Southampton, UK, Shantou University, China, and associated researchers from Jordan, Australia and the Czech Republic. The fieldwork of the study focused on 3 sites - the first two sites were Wadi Gharandal and an area near the village of Gregra, both situated within the Jordan Rift Valley itself.

The third site, Wadi Hasa, is located in the higher elevations of the Jordan Plateau. The term 'Wadi' is of Arabic origin and refers to a seasonal riverbed that typically only contains water during periods of heavy rainfall, explain the scientists in a published release on The Conversation.

“Our newly published evidence is a key piece of the puzzle that shows humans migrated using a northern route – using small wetland areas as bases whilst hunting abundant wildlife in the drier grasslands. Although previous studies have looked for large lakes as potential watering holes, in fact small wetlands were very important as staging posts during the migration,” added Professor Carling.

The team went about reconstructing the historical environmental conditions of the region by accurately dating specific sediment layers. To achieve this, they employed a technique known as luminescence dating, which allowed an estimation of the duratio during which sediment grains had been shielded from sunlight, thus enabling the determination of their age, reports The Daily Mail.

Sedimentary sections were analyzed, ranging from 5 to 12 meters (16.4-39.3 feet) in thickness, which unveiled a pattern of environmental fluctuations over time, encompassing alternating cycles of arid and humid conditions. Luminescence dating results indicated that these sedimentary environments formed between 125,000 and 43,000 years ago, implying the occurrence of multiple wet periods.

All in all, the fieldwork revealed that the Jordan Rift this valley once served as a 360-kilometer-long freshwater corridor, facilitating the northward migration of humans into Western Asia and their southward expansion into the Arabian Peninsula. Support for this northward expansion is also found in the renowned Skhul and Qafzeh cave sites located in Israel, where fossils of Homo sapiens and Levallois stone tools have been unearthed.

On the southern front, research conducted in northern Saudi Arabia provided evidence of a vast network of rivers and lakes that once existed in the region! This network allowed humans to access a lush Nefud Desert characterized by savannahs and grasslands.

Within the heart of the Nefud Desert, the lakeside site of Al Wusta has yielded human fossils and Levallois stone tools dating back to 85,000 years ago. Notably, these dates align closely with the 84,000-year-old Levallois stone tools discovered at Wadi Gharandal. Cumulatively, the research is yet another pointed reminder at “the intimate relationship between climate change and human survival and migrations”.

“The paleohydrological evidence from the Jordan desert enhances our understanding of the environmental setting at that time. Rather than dry desert, savannah grasslands would have provided the much-needed resources for humans to survive during their journey out of Africa and into southwest Asia and beyond,” concludes Dr Mahmoud Abbas, the study’s lead author from Shantou University, China.

Top image: Main; Wadi Gharandal riverine wetland along the Jordan Rift Valley. Inset of flaked stone handtool, found in the Jordan Valley. Source: Main; Mahmoud Abbas, Inset; University of Southampton

By Sahir Pandey