November-December 1996
November-December 1996
Roy Larick and Russell L. Ciochon
More than a century ago, Dutch paleontologist Eugene Dubois
suggested that human origins lay in Southeast Asia, and he soon found the
undeniably earliest hominid skeletal remains on the island of Java. In the
1930s, many more fossils of similar primitive character came to light near
Beijing, and the entire Asian collection became known as Homo erectus.
Presumably arising from an Asian ape, "upright man" had evidently
occupied a great swath of eastern Asia, and provided the logical precursor
to the more advanced and younger Neanderthal and Cro-Magnon (Homo sapiens)
fossils of Europe. In evolutionary terms, Homo erectus was thought
to have emerged in Asia and later dispersed to Europe.
During the 1960s, the eastern Rift Valley region of eastern Africa began
to yield contrary evidence in its many much older Australopithecus fossils
as well as an ample number of fossils from Homo. By the 1970s, human
origins were believed to lie in Africa, with a much later dispersal toward
East Asia. Movement from Africa to Europe came yet later. The new African
research, a collaborative effort among paleontologists, geologists, paleoclimatologists
and others, also began to ask about the timing and cause of human emergence.
In the light of new ecological theory and increasingly sensitive environmental
evidence, paleoanthropologists could now advance relatively complex behavioral
models.
Current evidence suggests that about 3.0 to 2.4 million years ago (mya),
the relatively cool, dry climate of tropical Africa presented challenging
new conditions for woodland-dwelling Australopithecus. In theory,
the cooler climate cleared out some of the woodland to form new open habitats.
It is at about this time that the earliest species of the genus Homo
emerged, between 2.5 and 2.0 mya, to exploit the new habitats as a rather
aggressive omnivorous scavenger.
Climate has been less useful for understanding the intercontinental dispersion
of Homo. Until recently, the earliest Homo fossils in Asia
appeared to be no more than 1.1 million years old, representing a time well
after emergence and not directly related to significant climatic events.
Paleoanthropologists have therefore explained dispersion as a separate stage
of development, and as the result of "internal" factors, such
as population saturation and technological advances in tool making and resource
scavenging.
Recently, however, we and our Chinese colleagues have contributed to what
has become a wave of new Asian fossil discoveries and technical re-analyses
that change this picture. In tropical and subtropical East Asia, the age
of newly discovered fossils of Homo and simple stone tools, as well
as some revised dates for known remains now approach 2 million years, nearly
1 million years older than previous estimations. In temperate west Asia,
a new hominid and associated tools reach 1.4 million years in age. This
new evidence extends the pattern of well-known contemporary eastern Mediterranean
archaeological sites northward to suggest a later--but still quite early--movement
to the more temperate areas of the Middle East and mid-latitude west Asia.
The new finds and age determinations give distinctness and complexity as
well as antiquity to the formerly late and amorphous pattern for Asian dispersal.
Our interest lies in the initial dispersal of early Homo from tropical
Africa eastward across tropical and subtropical habitats of south and East
Asia. In fact, early Homo now seems to have arrived in East Asia
so early that its African emergence and initial subtropical Asian dispersal
must be linked. Thus the factors that triggered the evolution of Homo
from Australopithecus also encouraged early Homo to leave
Africa, at least initially. We reconsider the new evidence for early dispersals
in the light of climatic, morphological, technological and behavioral factors
hypothesized for the emergence of Homo. We find that the striding
gait, the elementary stone tools and the simple, but expansive, pattern
of scavenging that characterizes the emergence of Homo also served
its initial dispersal. In contrast, later populations of Homo colonized
more temperate habitats under more complex and less obvious conditions.
© American Scientist 1996