South Africa’s Desert-Like Interior Might Have Been More Welcoming to Our Human Ancestors

The Cape of South Africa and its southern coast were once surrounded by thriving landscapes and abundant food, with long chains of caverns running along the area. Approximately 200,000 years ago, during a glacial phase known as Marine Isotope Stage Six (MIS6), these caves provided a refuge for a group of humans who may have been the only survivors of that ice age. While the coastal region has been extensively studied by archaeologists, the interior of South Africa has received less attention and was considered inhospitable and uninhabited during two subsequent ice ages, MIS3 and 2.

The interior of South Africa

A recent study conducted by archaeologist Brian Stewart from the University of Michigan suggests that the interior of the South African region might have been more fertile and temperate during the two glacial periods than previously believed. The research indicates that the area likely supported human populations living near a series of ancient lakes. Stewart’s study, funded by the National Geographic Society, presents a detailed timeline of the lakes’ age and stages, revealing traces of human activity throughout the region. The findings challenge the conventional assumption that human settlements were primarily concentrated along the coastline, while the interior, particularly the southern part of the Karoo Desert, was largely uninhabited for extended periods. Surprisingly, the research highlights the presence of widespread archaeology in the interior, indicating that human populations existed there. The study has been published in the journal PNAS.

However, in order to establish the archaeological significance of the region, it was crucial for the researchers to demonstrate the viability of human habitation there. To accomplish this, an international team of researchers from South Africa, the UK, and France conducted a thorough analysis of the area. They focused on studying expansive flat areas surrounded by higher ground, known as “pans” in Afrikaans, which were identified as ancient lake beds. The higher elevations encircling these pans were found to be the result of erosion and sedimentary deposits from past coastlines.

This discovery indicates that the region experienced a less arid climate during the studied time periods than previously believed. The presence of these lakes suggests that there must have been sufficient and sustained rainfall and humidity to keep them filled. Moreover, the more temperate climate supported by the lakes would have allowed for the growth of vegetation and the presence of animals, providing the necessary resources to sustain human populations.

Reconstructing the paleolakes

The researchers employed various techniques to determine the age and reconstruct the ancient lakes, coastlines, and lake bottom deposits, thus reconstructing the landscape of the region.

These techniques included radiocarbon dating, which uses the decay of radioactive carbon isotopes to estimate the age of organic material. Additionally, they utilized a method called luminescence dating, which involves measuring the radioactivity of small crystals of quartz or feldspar that has been shielded from light by sediment for thousands of years. When sediments undergo burial, the crystals within them capture and retain electrons from radioactive elements at a steady pace. By measuring the accumulated electrons in the sample and comparing it to the background radioactivity, scientists can determine the age of the sample.

The scientists utilized these techniques to determine the ages of sedimentary columns found in lakeshores and lake bottom deposits, known as lacustrine deposits. These deposits were discovered in and around a group of three pans spanning an area of approximately 100,000 square miles, which is roughly the size of Texas. Additionally, they dated the shells of freshwater mollusks that were scattered throughout the region and embedded within the sedimentary lake deposits.

One particular species of aquatic gastropod, Tomichia ventricosa, found in a pan called Swartkolkvloer, was analyzed within a column of lacustrine deposits. By radiocarbon dating both the deposits and the shells, the scientists determined that they belonged to two distinct time periods: approximately 39,000 to 55,000 years ago and around 31,000 to 34,000 years ago.

In another pan named Grootvloer, the researchers made a significant finding of freshwater mollusk species known as Unio offer. The presence of this species indicates the requirement of “perennial freshwater” and the presence of fish for its reproduction. By dating the shells and lacustrine deposits in this specific pan, it was determined that they originated around 20,000 to 22,000 years ago.

Ice age in South Africa

The researchers were able to estimate the size and depth of the ancient lakes by analyzing the height of the surrounding lacustrine deposits. For instance, they determined that the paleolake at Swartkolkvloer covered an area of approximately 83 square miles and had a depth of 59 feet, while the paleolake at Grootvloer was estimated to be around 17 square miles in size and 62 feet deep. Another pan called Alexanderfontein, located about 300 miles northeast near Kimberley, held a lake that measured approximately 13.5 square miles in area and 48 feet in depth.

Based on these findings, the scientists concluded that the lakes would have required a significantly different climate compared to the present conditions in the interior of South Africa. Using a hydrological model, they determined that evaporation rates in the region were 20% to 25% lower than today, and precipitation would have been over 200% higher at Swartkolkvloer and 88% higher at Alexanderfontein.

According to Stewart, there is evidence to suggest that various parts of the interior, from around 60 to 12,000 years ago, experienced sustained periods of significant water bodies in what was previously considered an arid and inhospitable environment. This period was generally known for its dryness and extremely cold winters, but the presence of large lakes during this time has been established.

The researchers propose that present-day regions with similar climates, precipitation patterns, and evaporation rates are likely found in northern Botswana, Zambia, and Zimbabwe. Drawing from this estimation and data obtained from a contemporaneous site known as Equus Cave, the researchers believe that large herbivores and predatory mammals would have thrived in this region.

A complex, prehistoric people

Human artifacts, including triangular points, bladelets, weathered ostrich shells, and other archaeological assemblages, are scattered alongside the ancient lakes. Many of these artifacts belong to the Middle Stone Age, which spanned from approximately 280,000 to 25,000 years ago, as well as the Later Stone Age, which extended from 25,000 years ago until European contact in the 15th century.

Stewart emphasizes the abundance of Middle Stone Age archaeology throughout the region, stating that it can be found everywhere, even by simply opening a car door and stepping outside. The extent of archaeological evidence is remarkable.

Furthermore, Stewart suggests that their findings have the potential to expand the area where archaeologists believe humans developed more complex behaviors. In recent decades, researchers have discovered evidence indicating that humans living in coastal South Africa exhibited early signs of behavioral complexity. It was previously believed that favorable climatic conditions and access to nutrient-rich seafood, particularly omega fatty acids, played a role in facilitating the development of modern behavioral patterns in this region.

The team’s research presents a challenge to the notion that favorable conditions for hunter-gatherer societies were exclusive to the coastal areas. Instead, their findings suggest that as climates shifted, including in the interior regions such as the present-day desert, these areas also provided favorable conditions for human populations. This challenges the previous belief that only coastal regions offered the necessary resources and climate for the development of hunter-gatherer societies.

Further research in South Africa

According to Stewart, their research represents a comprehensive study covering a wide area, with significant implications on a larger scale. It includes not only the coastal and mountainous regions that have traditionally dominated archaeological narratives but also the inland areas adjacent to these regions. Contrary to the prevailing perception of the inland areas as inhospitable, their findings suggest that these regions were actually favorable for human habitation during significant periods of time. However, further investigation is needed to explore the archaeological evidence within the pans and gain a better understanding of how people lived in those areas.

Originally published on Science Daily.

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