Home | English | | | UGC | RGC
  Launching Theme-based Research
  The Legacy of Meritocracy:
Peking University Undergraduates,
  Negotiating with Media Globalization:
The Impact of China's Accession to the WTO on Its Media and Telecommunications Industries
  Neuroimaging studies of reading disability in Chinese children
  Random Geometric Graphs and Their Applications
  Paleoenvironmental Interpretation of the Olorgesailie Formation, Kenya Rift Valley
  A Study on the Collaborative Virtual
Geographic Environment (CVGE) for Simulating Air Pollution in Pearl River Delta (PRD) Region






Prof. Owen sampling sediments from a trench at Olorgesailie, southern Kenya

Our human ancestors roamed across the continent of Africa for several millions of years and evolved in response to changing environments. Evidence of their activities is now preserved as stone tools and as fragmentary skeletons in areas favorable for preservation. This investigation has focused on one such location, in the southern Kenya Rift Valley, at a place called Olorgesailie, which was once the home of Homo erectus.

Abundant stone tools and one pre-human skull have been found in the Olorgesailie Formation — a series of lake, wetland, river and soil deposits that formed 1.2 million to 500,000 years ago. These ancient sediments provide a basis for understanding environmental change during an important period of human evolution. Several ideas have been proposed to explain the forces that drove the development of our ancestors. The Savanna Hypothesis, for example, suggests that our ancestors started to walk on two legs as a response to a sustained expansion of grasslands that opened up new habitats. In contrast, the Variability Selection hypothesis proposes that temporally variable conditions result in the replacement of habitat-specific adaptations by evolutionary trends that increased pre-human adaptability (increased intelligence, greater social complexity) and therefore allowed the development of flexible responses to shifting environments. This idea, originally suggested by Professor Rick Potts (Smithsonian Institute), implies that the driving force for human evolution is environmental instability.

This research project has attempted to identify just how much and how frequently environments varied during an important phase in early human development, which allows an assessment of the competing ideas concerning what has driven human evolution. The work was carried out on previously well-dated sediments that provided a time framework for environmental reconstruction and has involved a variety of geological studies including: field analysis of the sediments; mineralogy and geochemical characteristics; and especially the use of microscopic fossils, mainly single celled algae called diatoms. These live in rivers, lakes, swamps and damp soils with individual species being very sensitive to their environment (water chemistry, water depth, nutrients, light levels, and so on). Different types become common, or die out, as environments change. Importantly, they also posses silica skeletons that are easily preserved in sediments. Consequently, when they die and are buried they leave behind a record of past environments.

Scanning electron microscope image of Diadesmis confervacea – a shallow water diatom

Studies of the deposits at Olorgesailie have shown that a complex mosaic of habitats that changed rapidly and frequently characterized the area. These findings contrast with other studies that have argued that there was a stable period of expanded lakes through large parts of eastern Africa during the time period in question. In contrast, the southern Kenya rift experienced dry periods that alternated with wetter phases. Fresh-water lakes and swamps formed, became saline, and dried out only to return again. The ancestral humans that inhabited the area 1.2 million to 500,000 years ago would have thus experienced substantial environmental shifts that varied with seasons, decades, and over time spans of hundreds to thousands of years. These are conditions that argue against the Savannah Hypothesis and for Variability Selection.

The natural forces that once drove our evolution are still at work today. In the past, environments changed for entirely natural reasons with climate varying on seasonal, decadal and longer time scales. These forces also changed the face of Africa, expanding and shrinking deserts. For instance, lakes and rivers flowed across much of the Sahara Desert between about 10,000–4,000 years ago. As climates deteriorated African peoples were forced to migrate, leading, for example, to the introduction of early pastoralism to northwest Kenya about 4,000 years ago. Climate and environmental change is therefore normal as is the necessity for humans to respond physically over very long periods and culturally on shorter time scales. However, we now face new forces that are driven by our own activities,which have raised greenhouse gases in the atmosphere to levels not reached for hundreds of thousands of years. These changes have been geologically very rapid and will likely result in major environmental shifts. Given the evidence from Olorgesailie and other parts of Africa, it is perhaps worth remembering that as a species and as members of civilizations just how sensitive we are to our environment.

Prof. Richard B. Owen
Department of Geography
Hong Kong Baptist University