44 ARCHAEOLOGY • March/April 2018put them in a PET scanner, which measures the accumula-
tion of glucose, the body’s basic fuel, in different parts of the
brain. “The thought was that glucose would accumulate in
the neurons that were most active,” Stout says.
Experimenting with modern people to draw conclusions
about the deep past poses other problems. Stone toolmaking
isn’t a common skill in modern times, for example, but Stout
wanted to capture the brain activity associated with making
the tool, not learning how to make it. So before they could
be scanned, people needed to learn to knap flint—easier said
than done. We may sneer at the supposed simplicity of “Stone
Age” technology, but volunteers in one of Stout’s experiments
needed an average of 167 hours of practice to produce pass-
able Acheulean hand axes.
Today, a pile of broken rock 10 feet across and five inches
deep—more than 3 , 000 pounds of chipped flint—outside
Stout’s office at Emory testifies to the thousands of hours
volunteers have put into learning to make tools. “I can explain
golf in a few minutes, but getting your swing down can take
years,” Stout says. “Toolmaking is difficult to do,
comparable to a sports skill or playing a
musical instrument.”
In other experiments, Stout trained
participants to knap flint and then scanned
them in an MRI machine while they
watched videos of someone else making
tools. Using such workarounds, Stout,
Uomini, and others pinpointed areas
in the brain that were particularly
active during Acheulean toolmaking:
the right inferior frontal gyrus, for
example, a region that experiments
have shown helps with impulse con-
trol and juggling multiple tasks.
Stout also showed that toolmak-
ing is capable of rewiring the brain. In
another experiment, brain scans showed
that the more a person practiced knapping
flint, the more brain matter built up in the
regions responsible. And in a recently published
study, Stout worked with primate
specialists to show that the brain
circuitry connecting the right
inferior frontal gyrus to the rest
of the brain was much more devel-
oped in humans than in chimps.
Altogether, Stout argues, there
is powerful evidence that tool-
making helped shape the mod-
ern human brain. What Stout’sOur ancestors stuck with Acheulean-esque hand axes lon-
ger than any other tool type. The distinctive axes were used
for chopping and cutting all across Africa, Asia, and Europe
for nearly 1. 6 million years—from their appearance around
1. 7 million years ago to 100 , 000 b.c. The tools support a rich
tale. “I would argue that this is the most important period
in human evolution,” says Putt. “Anatomy, behavior, cogni-
tion—all point to a more human type of being.”T
he acheulean transition has sparked a long-
running debate: What role, if any, did toolmaking
play in our evolution? This is where it gets even
more interesting. Early hominids must have been capable
of making tools before they began making them. “You can’t
have the behavior occurring before you have the capacity to
produce that behavior,” says Emory University evolutionary
anthropologist Dietrich Stout.
But once toolmaking began, it may have been driven by
other abilities, coevolving with language, social interaction,
advance planning, and other behaviors. Hominids who
were able to quickly learn to make useful tools and
then teach their offspring the skill would have had
a better chance of passing their genes on. Natu-
ral selection, the theory goes, would favor the
toolmakers who were able to both learn
and communicate. “The idea is that stone
tools and language coevolved in humans,”
says Natalie Uomini, an archaeologist at
the Max Planck Institute for the Science
of Human History. “It’s one of the big-
gest open questions in human evolution
right now.”
Over the past two decades, archaeologists
have used neuroscience research to try to
move beyond speculation. The field has pro-
gressed in fits and starts since the 1980 s, when
machines were first used to look at human brain
activity in real time. Anthropologists suggested
the technology’s potential as a research tool as
early as 1990 , but it took another decade
for Emory’s Stout to publish the results
of the first stone tool experiments that
used a brain scanner.
Part of the delay had to do with
the limitations of the technology.
The most powerful and common
brain scanning devices are func-
tional MRI (fMRI) machines. MRI
scanners use massive magnets that
require people to lie absolutely still
during scans, making direct obser-
vation of toolmaking challenging.
Researchers have come up with some
creative workarounds. In one early
attempt, Stout had study participants
make flint tools for 45 minutes. He thenAn Oldowan tool (above) from the
site of Omo in southern Ethiopia
and an experimental Oldowan core
(left) fashioned by a participant in a
study designed to isolate the region of
the brain used for toolmaking