CLIMATE CHANGE alters vegetation and shifts shorelines. As our ancestors spread across Africa, Asia, and Europe, they learned to exploit the opportunities and survive the challenges they found in dynamic environments. Heirs to the curiosity and adaptability that set our genus apart, modern humans now occupy every imaginable habitat from the Equator to the Poles.
Four Million Years Ago - Hominids Take a Stand
Standing upright and waling on two feet is a basic requirement for inclusion in the human lineage. In 1925 Raymond Dart described Australopithecus africanus as a species that could do just that. Since then paleoanthropologists ahve unearthed remains of long-armed, short-legged, realtively small-brained early hominids from more than a dozen major sites in southern and eastern Africa, grouping then together as “australopithecines.”
Dramatic discoveries continue. In Chad, a 3- to 3.5-million-year-old partial jawbone has been assigned to the new species Australopithecus bahrelghazali, extending the geographic range of the genus 1,500 miles west of the East African Rift. Remains of Australopithecus anamenis collected at Kanapoi, near Lake Turkana in Kenya, stretch the australopithecine time span back a quarter of a million years. An even earlier creature, distinctive enough to be assigned to its own genus, has been unearthed at an Ethiopian site called Aramis. Ardipithecus ramidus, around 4.4 million years old, promises new insights into the split between the lineages of bipedal hominids and quadrupedal apes.
Olduvai Gorge - Source for Prehistory
Olduvai Gorge is a 30-mile-long gash in Tanzania's Seregeti Plain. ... Between 1.9 and 1.2 million years ago a salt lake occupied this area, its margins fringed with woodland and savanna. From 1.2 million to 620,000 years ago freshwater streams and small ponds laced the area. Layers of fossil-bearing sediments reveal a long-term shift to a more arid climate and help scientists correlate conditions in East Africa with global patterns of climate change.
For decades Louis and Mary Leakey and their colleagues scoured the gorge for traces of human ancestors, uncovering both significant fossil hominid specimens and primitive stone tools. Scientists digging in the gorge today are piecing together the context in which the Olduvai hominids lived and asking questions about diet, tool use, and competition for resource in a changing environment.
125,000 Years Ago - Exploiting a Climate of Opportunity
Many scientists emphasize the role o climate cycles in increasing and decreasing the territory accessible to humans since the emergence of Homo erectus from Africa at least 1.8 million years ago.
The map illustrates vegetation patterns about 125,000 years ago, at the warmest time of the last interglacial, based on the paleoecological date available. Modern coastlines are shown; sea level then may have been 20 to 30 feet higher than today. The areas of Africa shown as desert were probably more fragmented, with numerous lakes dotting the landscape. The earliest evidence of modern Homo sapiens occurs in Africa around this time.
Scientists debate the processes that might have established modern humans throughout the Eastern Hemisphere. Some believe that erectus populations developed into sapiens in several regions, with some genetic exchange among groups. Others contend that modern humans spread out of Africa beginning around 100,000 years ago, replacing the more ancient Homo populations they encountered.
65,000 Years Ago - Ice Age Routes to New Homes
The map shows glaciers, vegetation, and shorelines about 65,000 years ago. Glaciers cover nearly 17 million square miles of Earth's surface, and sea levels are more than 400 feet lower than today. Land bridges connect previously separated areas, enabling humans to move into new territories.
Even at this glacial maximum, however, Australia and New Guinea are isolated by the waters of the Java Trench and the North Australian and Weber Basins. The earliest firm evidence of human settlement in Australia dates from about 60,000 years ago, suggesting that some form of atbuilding had developed by that time.
Today - Prospecting for Hominids
Fossil hominid specimens come from sediments between 10,000 and bout five million years old. As the map indicates, dense plant growth blocks access to these deposits over much of Earth's surface. Finds are most likely in arid, sparsely vegetated regions where erosion has carved through layers of Earth. But even in promising areas significant discoveries are exceptional events. Only a tiny fraction of all organisms leave fossil traces anywhere. These constraints suggest that our curiosity about our past will probably always outstrip our ability to collect its remains.
