Did groundwater help early humans migrate out of Africa through Arabia?

Around two million years ago, as groups of Homo erectus began migrating beyond East Africa, their journeys were not simply a search for food or new territories. Survival also depended on finding reliable sources of water across landscapes repeatedly transformed by wet periods and prolonged droughts.

A new study suggests that groundwater and the springs it feeds may have played a crucial role in these early migrations, potentially helping explain which routes were accessible from East Africa through the Arabian Peninsula and into Eurasia.

Published on 30 October in Hydrogeology Journal, the study argues that water has received less attention than food availability and climate in discussions of human evolution, despite being essential to survival and long-distance movement.

To investigate its role, the two researchers reviewed published evidence from fossils, stone tools, ancient springs and lakes. They then reconstructed the water landscapes of East Africa and Arabia to identify locations where water may have remained available even after rivers and lakes dried up.

Groundwater may have created migration routes

Mark Cuthbert, professor of Earth and environmental sciences at Cardiff University and a co-author of the study, explains that surface water, including rivers and lakes, responds relatively quickly to declining rainfall. Large underground water reservoirs, however, can continue feeding springs for thousands of years after a dry period begins.

Some springs in East Africa may therefore have remained active for hundreds or even thousands of years during the driest phases of climate cycles, creating what researchers describe as water refuges within otherwise increasingly inhospitable landscapes.

The earliest evidence the researchers associate with groundwater use by human ancestors dates back approximately 4.4 million years in East Africa, including wet environments near springs and groundwater sources in Ethiopia.

In Tanzania, evidence dating back around 1.8 million years includes stone tools and early human remains found near wetlands and freshwater springs beside a saline lake unsuitable for drinking.

Cuthbert suggests that early humans may have learned to locate water by observing animals with greater experience finding it, including elephants and some primates.

They may also have dug shallow wells by hand in dry riverbeds to reach water trapped beneath the sand.

However, such behaviour would rarely leave archaeological evidence capable of surviving for millions of years. The absence of direct evidence, therefore, does not necessarily mean that early humans never accessed groundwater through these methods.

From Bab el-Mandeb into the Arabian Peninsula

One of the study’s most intriguing arguments concerns the route early humans may have followed when leaving Africa.

The researchers suggest that crossing the Bab el-Mandeb Strait, between present-day Djibouti and Yemen, may have been more favourable in terms of water availability than the traditionally proposed route through the Nile Valley and Sinai.

According to the study, the Nile was not necessarily a permanent, continuously flowing river in its present form between approximately 1.8 million and 800,000 years ago.

Parts of the proposed northern route also experienced high salinity, while the archaeological record contains relatively limited evidence of Acheulean stone tools, including characteristic hand axes, and early human fossils supporting this pathway during that period.

At Bab el-Mandeb, lower sea levels may have reduced the crossing distance to approximately 10 kilometres at certain times.

Nevertheless, crossing the strait would probably still have required some form of primitive watercraft, potentially constructed by tying logs together. The researchers acknowledge that this remains an unproven hypothesis.

They support the proposed southern route with the distribution of stone tools on both sides of the Red Sea and evidence of animals such as elephants historically inhabiting East Africa and Arabia. Early humans may have followed these animals in search of water and food.

Once early humans reached Arabia, Cuthbert suggests, they may not have needed to wait for every new wet period before continuing their journeys.

Large underground aquifers extending beneath the peninsula could have supplied a network of springs and oases during prolonged dry periods.

The study highlights a water-bearing geological formation stretching approximately 1,500 kilometres across Arabia, near areas containing substantial concentrations of stone tools in Saudi Arabia.

One such location is Saffaqah, where researchers have discovered approximately 25,000 Acheulean stone tools associated with groundwater-related sites.

The proposed migration route continues northward through Wadi Sirhan in Saudi Arabia, where Acheulean archaeological sites occur near springs and groundwater reservoirs, before extending towards the Azraq Oasis in Jordan and the Jordan Valley.

The researchers argue that the slow response of large aquifers to climate change could have allowed springs to continue flowing for thousands of years after wet periods ended.

These springs may have provided a chain of relatively reliable water sources that small groups of early humans could use while moving across otherwise arid landscapes.

However, the proposed route remains a hypothesis based on geological, hydrological and archaeological evidence rather than direct proof of a particular migration journey.

The findings suggest that understanding how groundwater behaved during ancient climate changes could provide an important missing piece in reconstructing the earliest movements of humans beyond Africa.