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PA L E O A N T H R O P O L O G Y
Whither the Neanderthals?
Richard G. Klein
within 10,000 to 15,000 years. The modern
human triumph depended on technological, economic, and demographic advantages that were apparently grounded in an
enhanced ability to innovate. This ability
probably appeared first in Africa, but debate continues on how rapidly it evolved
and whether it was rooted in biological
change or in population growth and social
reorganization. Fossils and artifacts are unlikely to resolve this issue, but genes underlying cognition might.
he Neanderthals are the longest more plausible ancestors of living humans.
known and best understood of all fos- Furthermore, surveys show that variants of
sil humans. In 1856, quarry workers mitochondrial DNA (5) and the Y chromocleaning out a limestone cave in the some (6) in living Eurasian humans derive
Neander Valley, Germany, found a partial exclusively from African variants that
skeleton for which the group is named. probably existed no more than 100,000
Today, several thousand Neanderthal bones years ago.
are known from more than 70 individual
Further support for this argument comes
sites. Yet, paleoanthropologists still debate from mitochondrial DNA extracted from
just how much the Neanderthals differed Neanderthal bones. The data indicate that Neanderthal Physical Form
from living humans and whether the differ- the last shared ancestor of Neanderthals and The Neanderthals were distinguished by
ences help explain why the Neanderthals living humans lived 500,000 to 600,000 large heads, massive trunks, and relatively
disappeared.
years ago (7). Non–sex chromosomes of liv- short, powerful limbs (1). Their average
Most Neanderthal specimens are isolat- ing humans may conceivably retain some brain size equaled or exceeded that of
ed skeletal elements, especially teeth and Neanderthal genes (8), but the combined modern humans, but their skulls also exjaws, but nearly every part of the skeleton fossil and genetic evidence suggests that hibit specializations that are unknown in
is represented in multiple copies. There are any Neanderthal contribution to living pop- any other people, fossil or living (9). These
also more than 20 partial skeletons from ulations was small. The Neanderthals may unique features underscore the likelihood
individuals of both sexes and different ages thus be regarded as a fascinating but extinct that the Neanderthals represent a divergent
(1). More than 300 archaeological sites side branch of humanity.
evolutionary lineage.
have yielded artifacts and broken-up aniModern humans invaded the west Asian
The specializations include the extraormal bones that illuminate Neanderthal be- part of the Neanderthal range about 45,000 dinary forward projection of the face along
havior and ecology (2).
years ago. They subsequently swept north- the midline, the tendency for the braincase
The Neanderthals evolved in Europe. ward and westward through Europe, to bulge outwards at the sides, a depressed
Some of their distinctive anatomical fea- swamping or replacing the Neanderthals elliptical area of roughened bone on the
tures already mark Euroback of the skull, and an array
pean fossils that are more
of bumps and crannies in the
than 350,000 years old (3).
vicinity of the mastoid proLong, low
Short, high
Short, flat face
Through a process of natucess. In addition, high-resoluLong face
braincase
braincase
mounted below
mounted in
ral selection and random
tion computed tomography
the
front
of
front of the
the braincase
genetic drift, they emerged
has revealed a singular conbraincase
in full-blown form by
figuration of the bony labyJuxtamastoid
130,000 years ago. From
rinth of the inner ear (10).
crest
then on, they were distribThese features apparently
Mastoid
uted more or less continuhad a genetic basis, because
process
No chin
Chin
ously from Spain to south0
5 cm
ern Russia; by 80,000 years
Neanderthal
Cro-Magnon
(La Chapelle-aux-Saints)
(Cro-Magnon 1)
ago, they had extended their
range to western Asia (see
the figure). They persisted
in Europe and western Asia
until at least 50,000 years ago and perhaps
in some places until 30,000 years ago.
Everywhere they lived, the Neanderthals were the immediate predecessors of
modern humans, and it has often been suggested that they were ancestral to living
populations. However, at the same time
that the Neanderthals occupied Europe and
western Asia, other kinds of people lived in
the Far East and Africa (4). The Africans
were anatomically much more modern
than the Neanderthals, and are therefore
T
The author is with the Program in Human Biology,
Stanford University, Stanford, CA 94305, USA. E-mail:
[email protected]
Realm of the Neanderthals. Approximate range of the Neanderthals and locations of some key
Neanderthal/Middle Paleolithic sites. (Inset) Reconstructed skulls of a Neanderthal and a CroMagnon.
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PERSPECTIVES
they are already visible in young children.
The labyrinth configuration was fixed even
before birth. There is no indication that the
specialized features attenuated through
time: The latest Neanderthals, 60,000 to
30,000 years ago, express them just as
strongly as their more remote ancestors.
Modern humans completely lack them. The
skull alone then is sufficient to preclude a
major Neanderthal contribution to living
human populations.
High activity levels and a strenuous lifestyle explain the power of Neanderthal
limbs. The short limbs and massive trunk,
which would conserve body heat, were
probably an adaptive response to the mostly glacial climatic conditions under which
the Neanderthals evolved. Among living
humans, such features particularly characterize Arctic peoples. The Neanderthals
had even more massive trunks and shorter
limbs, yet never faced true Arctic cold. The
degree to which they adapted physically
may reflect their limited ability to adapt
culturally.
Neanderthal Behavior and Ecology
The modern successors to the Neanderthals
are often known colloquially as the CroMagnons, after a French site where their
bones were uncovered in 1868. In general,
Neanderthal bones occur with artifact assemblages that archaeologists assign to the
Middle Paleolithic cultural (or artifactual)
complex, whereas Cro-Magnon bones occur with artifacts of the succeeding Upper
Paleolithic complex. The use of separate
names for the physical types and the artifact complexes allows for deviations from
the usual rule of association.
Middle and Upper Paleolithic people
shared many advanced behaviors, including a refined ability to flake stone, burial of
the dead (at least on occasion), an interest
in naturally occurring mineral pigments,
full control over fire, and a heavy dependence on meat (probably obtained mainly
through hunting). Both Neanderthal and
Cro-Magnon skeletal remains sometimes
reveal debilitating disabilities, indicating
that both kinds of peoples cared for the old
and the sick. There could be no more compelling indication of shared humanity.
Yet, archaeology also suggests many
important behavioral differences. Unlike
Upper Paleolithic Cro-Magnons, Middle
Paleolithic Neanderthals left little compelling evidence for art or jewelry. Their
graves contain nothing to suggest burial ritual or ceremony. They produced a much
smaller range of readily distinguishable
stone tool types; much more rarely crafted
artifacts from plastic substances like bone,
ivory, shell, or antler; and left no evidence
for projectile (as opposed to thrusting)
1526
weapons. Their cave sites are generally
poorer in cultural debris and richer in
bones of bears and other cave dwellers
(suggesting less dense human populations). They failed to build structures
durable enough to leave an archaeological
trace, and were confined to relatively
mild, temperate latitudes. Finally, the
Middle Paleolithic artifact assemblages
that Neanderthals produced varied little
through time and space. The Upper Paleolithic assemblages that Cro-Magnons made
varied far more and are the oldest from
which we can infer identity-conscious ethnic groups.
Hence, only the Upper Paleolithic anticipates the material record of historic
hunter-gatherers, and only Upper Paleolithic people were fully modern in the sense
that all historic people were.
Neanderthal/Cro-Magnon Contact
Consistent with an African origin for the
Cro-Magnons, radiocarbon dating suggests
that they displaced the Neanderthals about
45,000 years ago in western Asia and only
5000 to 15,000 years later in Europe. In
Europe, the Neanderthals may have succumbed much earlier in the far east
(Russia) than the far west (Iberia), but the
supporting dates are sparse. There is also
the ever-present possibility of minute, undetectable contamination with recent carbon, which can make a sample that is
50,000 to 40,000 radiocarbon years old appear 20,000 to 10,000 years younger.
Such contamination may explain radiocarbon dates that suggest the survival of
Neanderthals in southern Russia (11),
Croatia (12), and Spain (13) for 7000 years
or more after Cro-Magnons had appeared
nearby. Only the alternation of Neanderthal
and Cro-Magnon layers within a single site
could provide unequivocal evidence for
substantial chronological overlap. No
known site provides such alternation.
Wherever Middle Paleolithic and early
Upper Paleolithic layers occur in the same
site, the Upper Paleolithic layers directly
overlie the Middle Paleolithic ones, with no
indication for a significant gap in time. The
implication is that in most places the
Neanderthals disappeared abruptly.
Neanderthal/Cro-Magnon interbreeding has been suggested from occasional
fossils, including a recently discovered
Upper Paleolithic child’s skeleton from
Portugal (14). However, in each case, the
anatomical indications are at best ambiguous, and few experts recognize any hybrids. Evidence for cultural contact is also
sparse, except for one well-documented
case from central France. Here, a site occupied by Neanderthals shortly before
their disappearance has provided an unde-
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niable mix of Middle and Upper Paleolithic artifact types, including well-made
bone tools and jewelry (10). It also contains the only indisputable house ruin from
a Neanderthal site.
The mix may mean that Neanderthals
could imitate Upper Paleolithic/CroMagnon neighbors. But if Upper Paleolithic technology allowed more effective
use of natural resources and larger human
populations, it is puzzling that Neanderthals failed to adopt it more widely. If
they had done so, then their unique skeletal
traits and genes would be more obvious in
succeeding populations.
Cognition and Neanderthal Extinction
Except for the French site just cited, there
is little to suggest that Neanderthals could
behave in a modern, Upper Paleolithic way.
This inability may explain why they disappeared so quickly and completely. However, Neanderthal brains were no smaller
than those of modern humans. If there was
a difference in brain function, it resided in
soft tissue that cannot be inferred from
empty skulls. Hence, neither archaeology
nor fossils can reveal Neanderthal cognitive capacity.
This issue is important not only for illuminating Neanderthal disappearance.
Fossils show that between 130,000 and
50,000 years ago, the African contemporaries of the Neanderthals were more modern in anatomy, but archaeology suggests
that they closely resembled the Neanderthals in behavior (4). A change in brain
function about 50,000 years ago could explain why modern Africans subsequently
expanded to Eurasia.
The discovery that FOXP2, a gene involved in speech and language, achieved its
modern sequence less than 200,000 ago
years ago (15) provides tentative support
for such a change in brain function. A truly persuasive case may depend on the isolation of genes that are expressed differently in the brains of apes and people (16).
Many human gene variants will turn out be
very ancient, but if there was a brain
change around 50,000 years ago, one or
more variants should coalesce to about this
time. Fossil bones could provide a further
test, now that some have been shown to retain organic compounds that bear on brain
function (17).
The longest continuous debate in paleoanthropology is nearing resolution.
Modern humans replaced the Neanderthals
with little or no gene exchange. Almost
certainly, the Neanderthals succumbed because they wielded culture less effectively.
The main question that remains open is
whether Neanderthal genes explain their
failure to compete culturally.
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PERSPECTIVES
References
1. E. Trinkaus, P. Shipman, The Neandertals: Changing
the Image of Mankind (Knopf, New York, 1993).
2. P. A. Mellars, The Neanderthal Legacy: An Archaeological Perspective from Western Europe (Princeton
Univ. Press, Princeton, NJ, 1996).
3. J. L. Bischoff et al., J. Archaeol. Sci. 30, 275 (2003).
4. R. G. Klein, The Human Career: Human Biological and
Cultural Origins (Univ. of Chicago Press, Chicago, ed.
2, 1999).
5. M. Ingman, H. Kaessmann, S. Pääbo, U. Gyllensten,
Nature 408, 708 (2000).
6. P. A. Underhill et al., Nature Genet. 26, 358 (2000).
7. M. Hofreiter, D. Serre, H. N. Poinar, M. Kuch, S. Pääbo,
Nature Rev. Genet. 2, 353 (2001).
8. A. R. Templeton, Nature 416, 45 (2002).
9. A. P. Santa Luca, J. Hum. Evol. 7, 619 (1978).
10. J.-J. Hublin, F. Spoor, M. Braun, F. Zonneveld, Nature
381, 224 (1996).
11. I. V. Ovchinnikov et al., Nature 404, 490 (2000).
12. F. H. Smith, E. Trinkaus, P. B. Pettitt, I. Karanovic, M.
Paunovic, Proc. Natl. Acad. Sci. U.S.A. 96, 12281 (1999).
13. J.-J. Hublin et al., C. R. Acad. Sci. Paris Ser. IIA 321, 931
(1995).
14. C. Duarte et al., Proc. Natl. Acad. Sci. U.S.A. 96, 7604
(1999).
15. W. Enard et al., Nature 418, 869 (2002).
16. W. Enard et al., Science 296, 340 (2002).
17. H.-H. Chou et al., Proc. Natl. Acad. Sci. U.S.A. 99,
11736 (2002).
BIOMEDICINE
cess production. The trabecular meshwork
lies at the intersection of the cornea and iris,
which forms the iridocorneal angle or simply
the “angle.” Glaucomas are classified, in part,
by the appearance of the iridocorneal angle:
open, closed, or developmentally abnormal.
To lower intraocular pressure, we use
Wallace L. M. Alward
topical medications, systemic medications,
laser procedures, and microsurgihe optic nerves of the eye provide
cal procedures to decrease aquemuch of the brain’s sensory input,
ous production or enhance aquecarrying 38% of all nerve fibers that
ous outflow. Current glaucoma
enter or leave the brain (1). The two optic
treatment, although generally efLens
nerves transmit nerve impulses along more
fective, is broad and nonspecific
Iris
than 2 million axbecause we don’t fully underons. In individuals
stand the mechanisms by which
Enhanced online at
the trabecular meshwork reguwww.sciencemag.org/cgi/ afflicted with glaucontent/full/299/5612/1527 coma, these axons
lates aqueous outflow.
gradually die, resultDevelopmental abnormalities
ing in the loss of peripheral vision and ulof the iridocorneal angle that retimately central vision. Glaucoma, the
sult in glaucoma, such as those
leading cause of irreversible blindness in
studied by Libby and colleagues,
Ciliary
the world, currently affects nearly 70 milare rare. In Western countries,
body
Cornea
lion people worldwide and has blinded
primary congenital glaucoma ocVitreous
body
about 7 million people (2). Although optic
curs in about 1 of 10,000 births
Trabecular
Sclera
meshwork
neuropathy seems remote from the devel(6). Mutations in the gene encodopmental ocular defects described by
ing the FOXC1 transcription facSchlemm’s
Libby et al. on page 1578 of this issue,
tor cause an even rarer form of
canal
their study provides hope for a more effecdevelopmental glaucoma called
tive treatment for glaucoma (3).
Axenfeld-Rieger
syndrome.
Angle of repose. A fluid called the aqueous humor is produced
Given that glaucoma is an optic neu- in the ciliary body of the eye, circulates throughout the anteri- However, in societies in which inropathy, logic suggests that the best thera- or part of the eye, and then exits primarily through the trabec- termarriage is commonplace, pripeutic strategy would be direct treatment of ular meshwork. This meshwork resides in the angle formed by mary congenital glaucoma is
the nerve to promote regeneration of lost the iris and the cornea—the iridocorneal angle, or simply the much more prevalent (6).
axons. Like the spinal cord, however, the “angle.” One of the hallmarks of primary congenital glaucoma Although there are far fewer cashuman optic nerve cannot be repaired (4). is a high intraocular pressure due to aberrant development of es of developmental glaucoma
Neuroprotection and neuroregeneration are the trabecular meshwork and consequent poor drainage of the than of adult glaucoma, each case
major areas of glaucoma research that in aqueous humor.
of childhood blindness extracts a
many ways parallel spinal cord injury rehuge personal and societal cost
search. No method yet exists to treat the the front of the eye. The lens and cornea are when compared to blindness that develops
optic nerve directly (4). Ophthalmologists metabolically active, but being transparent late in life.
must therefore protect the nerve by treating tissues, they lack blood vessels. To nourish
Research has identified mutations in
the only known modifiable risk factor for these structures and to remove waste, the an- several genes that are involved in pediatric
glaucoma: intraocular pressure. Lowering terior segment of the eye contains a circulat- and adult glaucoma. Although these genes
the intraocular pressure helps to guard ing clear fluid—the aqueous humor (see the are associated with a wide variety of ocular
against further glaucoma damage, even figure). Produced by the ciliary body, the phenotypes—ranging from a normal apamong those who have sustained damage aqueous humor circulates throughout the an- pearance to the loss of the iris and fovea—
despite a normal intraocular pressure (5).
terior portion of the eye and exits primarily all can cause an elevated intraocular presAlthough the optic nerve is at the back of through the trabecular meshwork into sure due to impairments in the trabecular
the eye, intraocular pressure is regulated in Schlemm’s canal and finally the venous cir- meshwork. The molecular mechanism by
culation. It is the balance between aqueous which mutations in these genes affect the
production and outflow that determines the trabecular meshwork remains unclear.
The author is in the Department of Ophthalmology
pressure within the eye. An elevated intraocLibby and colleagues found that mice carand Visual Sciences, University of Iowa College of
ular
pressure
almost
always
results
from
derying
mutations in the genes encoding FOXC1
Medicine, Iowa City, IA 52242, USA. E-mail: wallaceficient outflow of the aqueous humor, not ex- and CYP1B1, a member of the cytochrome
[email protected]
A New Angle on
Ocular Development
CREDIT: PRESTON MORRIGHAN/SCIENCE
T
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