|Themes > Science > Paleontology / Paleozoology > Paleozoology > Fossil Hominids > Hominid Fossil Sites|
Recently, with more powerful geological dating methods based on fluctuations in the earth's magnetic field or electron spin resonance, the earliest Homo erectus fossils from China have been dated to 1.9 million years ago. This requires an even earlier date for the emergence of Homo ergaster in Africa, implying humans first evolved about 2.5 million years ago.
Climate studies show a cooling of the climate in Africa from around 3 million to 2.4 million years ago. This cooler, drier climate would have cut back a significant part of the lush northern African forests, opening up vast areas of grassy plains and restricting the range of australopithids adapted to forest habitats. These grasslands and the many resources they afforded for opportunistic scavenging were the ecological niche invaded by the new species Homo.
But scavenging is a migratory life, tied to the hunting patterns of predators and the herds of game they prey on, to fluctuations in water supplies, to seasonal shifts in the requirements for shelter and plants. The increased stature and brain size of Homo rudolfensis and Homo ergaster suggest humans adapted rather quickly to these new rigors. Successfully coping with fluctuating environments created the skills to adapt to a wider range of new environments, making it feasible for the migratory humans gradually to follow resources and herds of game into an ever widening range of habitats across the Middle East and southern Asia.
This was only the first of many human migrations, which fall into three distinct geological periods:
Around 120,000 years ago Homo sapiens emerged as a new species, most likely in central East Africa, and from there migrated into the Middle East, south Africa, Europe, central Asia, and finally into the New World. To reach the Bering Strait from Africa by 14,000 years ago, humans would have had to wander no more than one mile every eight years. -- The timing of Ice Age coolings, and the amount they lowered ocean levels, specifies the geologic periods in which it was possible to migrate to land masses otherwise separated by water.
The map below shows in greater detail the major fossil and archaeological sites in the Old World. Careful geological dating of these sites, and close comparison of the tools and bones found at different sites, are helping paleoanthropologists to map when and where different species appeared, and to tie these sites together into migratory patterns. Climate data and the migratory patterns of other fossil mammals provide corroborating evidence for the overall sequence of human movements.
Both maps present the ocean coastlines and inland tracts of vegetation as they likely appeared around 20,000 years ago, when the last Ice Age reached its maximum and sea level had dropped more than 20 feet below where it is today. By that time modern humans had radiated out of Africa into Europe and most of Asia, including Australia. Climate affected vegetation and rainfall to a considerable degree, and these wide variations stimulated human evolution through human migration. The backwater of human evolution, eastern Homo erectus, lived in parts of Asia where ecology varied much less with climate than it did in Africa and Europe.
It's interesting that several fossil sites from Homo erectus up to modern humans were located near seacoasts at the time of their habitation. There is good evidence that oceangoing boats were constructed by humans by 60,000 years ago. We tend to think of early humans as hillside "cave dwellers" and in inland areas they often were; but they were also early voyagers and harvesters on the waves.
Unfortunately it is very difficult to assess the importance of the oceans to human migration. Because sea level during the ice ages was much lower than it is today, most prehistoric coastlines are now covered by water. The few places where littoral habitations have been recovered are in areas where caves were located in seaside cliffs or hills.