Clues to early human behaviour
JOHN NOBLE WILFORD
At a rock shelter on a coastal cliff in South Africa, scientists
have found an abundance of advanced stone hunting tools with a tale to
tell of the evolving mind of early modern humans at least 71,000 years
ago.
The discovery, reported in the current issue of the journal
Nature, lends weight to the hypothesis that not only did anatomically
modern Homo sapiens emerge in Africa but also, to a previously
unsuspected extent, their cognitive capacity for abstract and creative
thought and the conception of increasingly complex technologies
associated with modern human behaviour.
The report describes the stone tools as microliths, thin blades
about only an inch long that could be affixed to wood or bone. These
tipped projectiles were either arrows propelled by bows or, more likely,
spears launched by atlatls, wooden extensions of the throwing arm that
act as a lever, imparting greater speeds and distances to the weapon.
This technology, the researchers said, may have been pivotal to the
success of Homo sapiens as humans left Africa and entered Eurasia some
50,000 years ago, encountering Neanderthals who were limited to
hand-thrown spears.
The new evidence appeared to answer some critics who have
contended that previous findings of early modern human behaviour in
Africa have been spotty and short-lived. The rock shelter excavations at
Pinnacle Point, near Mossel Bay, east of Cape Town, show that this
micro-blade technology continued over 11,000 years, until 60,000 years
ago. The report says the technology was also “typically coupled to heat
treatment” processes in shaping sharp and durable blades that persisted
for nearly 100,000 years.
One of the authors, Curtis W. Marean, director of the research
and a paleoanthropologist at the Institute of Human Origins at Arizona
State University, said, “Every time we excavate a new site in coastal
South Africa with advanced field techniques, we discover new and
surprising results that push back in time the evidence for uniquely
human behaviours.”
Prior investigations showed that this microlithic technology
appeared briefly between 65,000 and 60,000 years ago and then seemed to
vanish. Such thin blades had not been found in abundance until about
20,000 years ago.
Marean said in a telephone interview that while some
archaeologists were still sceptical of a strong African role in modern
human behaviour, there was diminishing support for the more Eurocentric
“creative explosion” concept, born of bedazzlement over the cave art and
fine tools of Upper Paleolithic Europe, which became widespread after
the arrival of modern humans.
“Ninety per cent of scientists are comfortable that fully modern
humans and human cognition developed in Africa,” Marean said. “Now they
have moved on. The questions are, how much earlier than 71,000 years did
these behaviours emerge?”
Like many other archaeologists, Marean and his team have
concentrated their investigations in the caves and rock shelters
overlooking the Indian Ocean. In a global ice age beginning 72,000 years
ago, many Africans fled the continent’s arid interior, heading for the
more benign southern shore. Access to seafood and more plentiful plant
and animal resources may have increased populations and encouraged
technological advances, Marean said.
Richard G. Klein, a paleoanthropologist at Stanford University
who has favoured a more sudden and recent origin of modern behaviour,
about 50,000 years ago, questioned the reliability of the dating method
for the tools, noting that “there is another team that has already
argued for a much longer” time period for the toolmaking culture.
The hypothesis of earlier African origins of modern human
behaviour and cognition has been gaining strength over the past decade
or two. Two archaeologists, Alison S. Brooks of George Washington
University and Sally McBrearty of the University of Connecticut, led the
charge with publications of their analysis of increasing evidence of
African art and ornamentations expressing a modern cognitive capacity
and symbolic thinking.
In a commentary accompanying the Nature report, McBrearty, who
was not involved in the research, wrote that she believed that “modern
cognitive capacity emerged at the same time as modern anatomy and that
various aspects of human culture arose gradually” over the course of
subsequent millenniums.
