like to imagine a Pygmalion-like experiment that involves releasing
a Neandertal in the New York subway. Groomed, slipped into a specially
tailored Armani suit, and grasping a cell phone instead of a flint,
could he pass as a modern human?
the average New Yorker might not look closely enough to discern the
distinctive Neandertal body hidden beneath the suit--barrel-chested,
short-legged, and strong as an Olympic powerlifter. But even the most
indifferent subway rider couldn't look a Neandertal in the face without
a small shock. Eyes set deep beneath an overhanging brow ridge. A
short, receding forehead. A face that juts forward from the rest of
the skull, almost forming a snout. An enormous nose--wide, long, and
protruding, a combination found in no modern humans. Massive jaws
and teeth, particularly those at the front of the jaw--but no chin.
Since Neandertals were discovered about 150 years
ago, their reputation has undergone more revisions than Richard Nixon's.
Scientists have battled over what Neandertals looked like, how they
lived, and where they belong in our family tree. Today, some of these
once-hot controversies have cooled into agreement. Most anthropologists
concur that if we could look a Neandertal in the eye, we would not
be looking into the face of an ancestor. Reflecting this view, modern
humans (Homo sapiens), who first appeared in Africa about 140,000
years ago, are now classifed in a different species from the Neandertals
(Homo neanderthalensis), who inhabited Europe, western Asia, and the
Middle East from about 300,000 years ago to 30,000 years ago.
But the field hasn't gone cold. Just as many questions
remain unanswered about the Neandertals and continue to provoke research
and passionate debate. For example, Neandertals loom in our imagination
partly because of their exaggerated facial features. But why did Neandertals
evolve this ugly mug? What function did the bulbous nose, protruding
face, and enormous jaws serve?
Robert Franciscus of Stanford University has been studying the Neandertal
face for more than a decade, trying to understand its unusual architecture.
He specializes on the nasal and facial anatomy of Neandertals, and
on what we can learn about human evolution from them. (To his embarassment,
a colleague approached him at his first scientific conference and
said, "Hey, you're the nose guy!") To fathom why Neanderthals had
this combination of features, Franciscus says you need to look at
what Neandertals did with their mouth--besides eat.
Although Neandertals manufactured a wide variety
of stone tools, from heavy hand axes to delicate blades, the mouth
was a key supplement to their tool kit. From microscopic grooves and
wear patterns on Neandertal teeth, scientists conclude that the mouth
doubled as a vise for gripping the end of a stick while the hands
shaped the other end, and as a tanner's mallet for softening and working
animal skins. Straight scratches on the front teeth suggest that Neandertals
held food in the mouth while cutting it with stone tools. Continual
heavy use gradually eroded the teeth, so that "by the time Neandertals
reached their late 30s and early 40s, their teeth were worn down to
essentially nothing," Franciscus says. Only smooth nubs projected
beyond the gumline.
Hard, frequent biting may have created another,
more serious problem: strain on the facial bones. According to anthropologist
Yoel Rak of Tel Aviv University, the Neandertal face represents an
evolved solution for dissipating this stress. Over many generations,
he says, the bones of the face and jaw became thicker and larger in
response to the strain from biting. This shoved the face forward.
Rak likens the Neandertal face to a pair of swinging doors that had
been pushed partway open. His hypothesis, which he set forth in a
1986 paper, also explains the large Neandertal nose: as the face got
bigger, the nose enlarged along with it, just as a nose painted on
a balloon would grow as the balloon filled with air.
One skull feature to which Rak called attention
is the canine fossa, the hollow just below the human cheekbone. It's
absent in Neandertals. (No Neandertal could ever achieve the sunken-cheeked,
fashionably starved look coveted by today's models.) Instead, a wall
of bone continues straight down to the teeth--an arrangement Rak claimed
strengthened the upper jaw.
However, Franciscus points out one implausibility
in this adaptive story. For natural selection to favor a stronger
face, weaker-faced Neandertals must have paid some penalty in survival
or reproduction--say, they often fatally shattered their skull while
working a stick or gnawing a skin. If Neandertals--or their ancestors--did
regularly suffer this kind of injury, the fossil record shows no trace
the bite-stress hypothesis gained some support among anthropologists,
because it explained the Neandertal face as well as any other hypothesis
did. Franciscus's recent research focuses on a crucial but untested
assumption of Rak's hypothesis--that Neandertals could bite hard enough
to create stresses that would require reinforcement and remodeling
of the skull. To determine whether the face might be stressed during
biting, Franciscus needed to measure how much force was produced by
the muscles that close the jaw, as well as the strength of the bite.
But how could he calculate the power of long-decayed muscles when
he could only look at old bones?
Fortunately, muscles leave traces on bones that
allow anatomists to deduce not only where they joined to the skeleton
but also how large they were. These "muscle scars" are small ridges
that form on the bone at the point where the muscle attaches. Muscle
scars can change size within an individual's life, depending on how
vigorously the muscle is used. The more frequent and forceful the
muscle's contractions, the more bone is deposited on the muscle scar
for reinforcement, and the larger the scar becomes. By looking at
the muscle scars on preserved skulls, Franciscus was able to identify
the points of attachment for the three muscles that close the jaw
and get a good idea of the muscles's size.
Working with Stanford mechanical engineer Carol
Kallfelz-Klemish, Franciscus collected data for 31 different skulls.
Two were Neandertals (one 40,000 to 50,000 years old, the other about
50,000 years old). Three were "early" modern humans (13,000, 20,000,
and 90,000 years old), ancient members of our species. And 26 were
"recent" human skulls, all less than 1,500 years old. Twenty of these
skulls came from Ohlone Indians, a tribe that not only ate predominantly
gritty and tough food, but also used their teeth to soften skins--just
Franciscus and Kallfelz-Klemish used a digitizer--a
machine that gives the three-dimensional coordinates for a particular
point--to enter into a computer the size and attachment sites of each
muscle. By applying standard engineering formulas to the data, they
could then calculate how much force each muscle produced, how much
force was placed on the jaw joint, and how much total force went into
The surprising results, which Franciscus and Kallfelz-Klemish
have submitted to the American Journal of Physical Anthropology, undermine
the view of Neandertals as particularly hard biters. Although Neandertals
could produce larger bite forces than recent humans, they were equaled
by one of the early modern humans and surpassed by the 90,000-year-old
skull of a Neandertal contemporary. What's more, when Franciscus calculated
the efficiency of biting--the bite force divided by the force generated
by the muscles--the value was actually lower in Neandertals than in
early modern and recent humans.
In other words, for a given amount of muscular contraction,
Neandertals actually didn't bite as hard as either the early modern
humans or the recent humans. Not what you'd expect if natural selection
for biting power were driving the evolution of the face.
To show that this technique gave realistic results,
Franciscus compared his estimates for the bite force of recent humans
to actual measurements taken on living, biting people. (Scientists
had them clamp down on a force-measuring machine.) Since his estimates
fall within the range of measured values, he's confident he's on the
Kallfelz-Klemish concluded that during Neandertal and human evolution,
natural selection was acting not to increase bite force, but to match
it to body size. The robust Neandertals, with their larger jaw muscles
and massive skulls, did bite somewhat harder than recent humans, such
as the Ohlone Indians, and about as hard as the early modern humans,
who were also more robust than recent humans. But when he and Kallfelz-Klemish
adjusted their calculations to account for the greater size of the
Neandertal skull, the Neandertals' bite force proved no greater than
that of the other groups.
Franciscus quickly adds several caveats. Clearly,
it isn't possible to draw definitive conclusions from just two Neandertal
skulls. He plans to extend the analysis by measuring more early modern
human skulls and at least one more Neandertal skull. Ideally, he'd
like to work with many Neandertal skulls, but few fossils are in good
enough shape for this kind of analysis. Even the skulls he did use
weren't complete--some of the bones had been reconstructed based on
other Neandertal skulls. "You have to work with what's available,"
says Kallfelz-Klemish, "It makes you be creative."
To bolster his conclusions, Franciscus would also
like to measure the actual Neandertal fossils, which are squirreled
away in museums, instead of the plastic casts he relied on for this
study. Although the casts are made of shrink-resistant plastic and
look remarkably accurate, they may not have captured all of the subtleties
of skull anatomy, he says.
Franciscus and Kallfelz-Klemish hope their work
will encourage anthropologists to use quantitative, rather than descriptive,
methods for testing hypotheses about evolutionary questions. "The
point of the article is that we won't be able to go back to the kinds
of analyses we once did . . . We're hoping it's a landmark study,"
In a field where almost every interpretation or
assertion provokes controversy, anthropologists agree that Franciscus
and Kallfelz-Klemish have made a significant advance. World-renowned
Neandertal expert Erik Trinkaus, a professor of anthropology at Washington
University in St. Louis, praises the study for its rigor and creativity.
"Other people have done this at a cruder level," he says, but Franciscus
and Kallfelz-Klemish "have elegantly demonstrated that high levels
of bite force are unrealistic for Neandertals." Anthropologist Milford
Wolpoff of the University of Michigan, who disputes Trinkaus's views
on the Neandertals's fate and relationship to humans, concurs. "He
[Franciscus] has bitten off a good project," Wolpoff says. "If we
can see what the muscles are doing, it's a better way of understanding
If the extreme facial features of Neandertals weren't
part of an adaptive package to dissipate the forces of biting, what
was their function? An older hypothesis, proposed in the 1960s by
Yale University anthropologist Carleton Coon, sees the Neandertal
face as an adaptation to the cold climates of northern Europe and
Asia. Blood vessels that deliver blood to the brain pass near the
nasal cavity--the chamber behind the nose where inhaled air is warmed
before traveling to the lungs. According to Coon, the Neandertals
needed a large nose and a particularly large nasal cavity to avoid
chilling these blood vessels.
some anthropologists accept this argument, Franciscus doesn't buy
it. For one thing, among modern people who live in cold climates--Northern
Europeans, for instance--long, narrow noses or small, flattened ones
are the rule. These shapes help minimize the loss of heat from the
Instead, Franciscus thinks the Neandertal face may
represent an adaptation for having large teeth. In the days before
dentures, losing all your teeth would be fatal. This is a more plausible
cause of death than facial breakage, Franciscus says. Under the stresses
Neandertals placed on their teeth, modern humans' teeth would wear
away by the mid-teens. By starting out with bigger teeth, a Neandertal
could live longer. But to have big teeth, they needed a big jaw to
hold them, which also meant a big face.
If Franciscus's explanation proves correct, an interesting
avenue of speculation opens. The Neandertal mouth could have served
yet another function: a sexual advertisement. When big teeth mean
longer life, a broad smile could reveal as much about a male's prospects
as an Armaini suit and cell phone do today. And the Stone Age equivalent
of Brad Pitt's dimpled chin could have been buck teeth or an overbite.
Of course, fossils can't tell us whether male Neandertals grinned
habitually, or even at all, but we can imagine another kind of experiment
. . . .
the subway, the commuters turn to gawk at the short, well-dressed
figure. Standing amid the grim-faced New Yorkers, the Neandertal is
smiling--a big, toothy leer.