For a beginning read the following article on an African Emergence and the Early Asian Dispersal.
This begins the story of the last one million
years of hominid evolution. The story begins with the emergence of a hominid
known as Homo erectus around 2 million years ago. The story of what
happened to this hominid in the last 1 million years becomes not only complex
but controversial as Homo erectus moved out of Africa and spread
into Europe and Asia. The story is one of variation and continuity. The
controversy stems from the ways this story can be put together given the
range of diversity in the archaeological and fossil records.
The story includes a look at the emergence of Neandertals. A figure of prehistory
with a misunderstood and tainted past. Is the Neanderthal brutish and a
dimwit who was not directly ancestral to modern Europeans? Or was Neandertal
in some way related to the people of Europe today?
The story of variation begins with the emergence of Homo erectus
around 2.0 million years ago. Our story begins in Africa where a number
of different types of hominids were evolving. While there are some specialized
forms known as Paranthropus boisei and robustus, there appear
to be other forms with different statures and different brain sizes. To
a large extent these forms represent a growing range of variation in the
hominid world following 2.5 million years ago when there was a dramatic
climatic change. This climatic shift led to an increasing savanna environment
in eastern Africa where our story takes place. This shift forced new adaptations.
What is clearest is that hominid brain size expands relatively rapidly at
this time - more than a 25% increase..
Following 2.5 million years ago, the record in east Africa is one that reflects
a puzzle. As evidence is compiled, paleoanthropologists are trying to sort
out the variations that are found. There is a trend for paleoanthropologists
to give new names to these finds. A number of names have been given to these
fossils such as: Homo habilis ("handy man"), Homo ergaster
("work man"), Homo rudolfensis, and Homo erectus.
These names may seem confusing, but they reflect differences in individual
finds in some cases. Over time one expects that scientists will form a consensus
on what these mean.
It is clear that some form of Homo erectus with a larger brain in
the range of 800 ml migrated out of the Africa. The timing of this event
has traditionally been placed at around 1.0 million years ago. However,
recent dating of finds from Java as sites called Sangiran and Mojokerto,
cast a new light of the timing of this migration. Dates from this part of
the world point to a much earlier migration; perhaps as early as 1.6 to
1.8 million years ago. There is other information to support this earlier
sequence. A site in Russia (Dmanisi) may be as old as 1.6 million years.
There also are some crudely made artifacts found in Pakistan that have been
tentatively dated as 2.0 million years old. These dates place the migration
out of Africa at an early stage of Homo erectus evolution. At this
stage, one must question whether these early dates are valid and we must
recognize they fly in the face of traditional interpretations that place
the migration out of Africa much later.
This
map shows the important sites pertinent to the first migration out of Africa.
The question becomes one of timing. The first scenario would place a migration
at nearly 1.6 to 1.8 million years ago (mya). This would match the dates
for Dmanisi and Java (Sangiran and Mojokerto). The second scenario would
place the migration much later, nearer to 900,000 years ago. This would
match the evidence of China, Europe, and later dates for Java (800,000 years
ago). Since there nearly a 1.0 million year difference between the two possible
times when the first hominids moved out of Africa, the scenarios have dramatically
different implications. Recent finds in China suggest an earlier date for
the arrival of Homo Erectus there too. Teeth from what have been identified
as Homo ergaster suggest the presence of Homo erectus in China
nearly 1.2 (or possibly earlier) million years ago. This would be consistent
with the dating of fossils in Java to the south.
This leaves us with evidence suggesting a migration out of Africa at stage nearly 1.5 million years ago. It also leaves us with a picture of this migration that pushes these migrants eastward. Dating of materials in Europe suggests a separate process of spread into what we can think of as the cul-de-sac. Europe would have been cold and inhospitable and it may be that the Homo erectus spreading out of African very early could not adapt to the cold climatic conditions in this region.