See the article"Between 140,000 and
50,000 years ago, both Neandertals and early modern humans periodically
inhabited the coastal woodlands and inland steppe of the Near East. The
archeological remnants of the behavior of these two groups—mostly in
the form of stone tools and animal bones—are so similar that were it
not for the fact that both groups occasionally buried their dead in the
caves in which they lived, we would not have known that they derived
from more than one population. Although morphologically and
taxonomically distinct, both types of human are associated with Middle
Paleolithic (Mousterian) stone-tool assemblages that cannot be
differentiated clearly on the basis of technological and formal
typological attributes (1, 2). But although the archeological record
indicates behavioral similarity, and by inference adaptive similarity,
between Neandertals and early modern humans at this time, functional
morphological studies of the human skeletons suggest quite a different
story. Detailed study of parts of the skeleton that alter their
material and geometric properties during life in response to activity
or that show degenerative changes from wear and tear suggest important
behavioral differences between these groups (3, 4). This situation
raises perplexing questions. If both tool assemblages and the malleable
aspects of the skeletons of the humans who made, used, and discarded
those tools are monitoring prehistoric behavior (5), why do these two
data sets produce such contrasting interpretations of that behavior?
And if behavioral contrasts did exist, did these contrasts serve to
give one group a competitive advantage? This later question is
important, because many see the Near Eastern early modern humans as the
source population from which modern humans migrated into Europe
approximately 36,000 years ago—leading to the extinction of the
Neandertals soon after. Evolutionary models that posit a single center
of origins for modern humans (such as Africa) with subsequent
geographic expansion of modern humans and replacement of
indigenous archaic populations (such as the Neandertals) rely on the
notion of adaptive superiority of the invading modern humans. Might
there then be indicators of a competitive edge to early modern human
adaptive strategies in the Near East? By focusing on skeletal
morphology that reflects manipulative behavior, the paper by Niewoehner
(6) in this issue of PNAS provides an important connection between
morphology and the production and use of technology. Although many
questions yet remain, this study represents an important step in
resolving contradictions in our behavioral interpretations of the
fossil and archeological records of the Near Eastern Middle Paleolithic
and in delineating the adaptive characteristics of both groups of
Mousterian humans.
On the basis of a multivariate analysis of three-dimensional
landmark data from carpal and metacarpal joint surfaces of Neandertals
and Near Eastern early modern humans, Niewoehner (6) concludes that
important manipulative differences existed between them—differences
not in dexterity but in grip strength and the ability to resist forces
incurred in certain grip positions. These differences indicate
contrasts in the habitual manipulative repertoires of the two groups.
Specifically, details of the form of the base of the thumb, index, and
middle finger in the modern humans from Skhūl and Qafzeh Caves
indicate a hand that was, like ours, well adapted
to withstand forces acting on the hand during oblique power gripping
(as in gripping a hammer handle). Neandertals, in contrast, had hands
well suited to forceful transverse power grips (as when gripping a
hammerstone), as indicated by the greater leverage of their thumbs,
enlarged crests for the muscles of finger flexion, broad finger tips,
and lack of specializations in the midhand (carpometacarpal joints) to
resist obliquely oriented reaction forces (Fig.
(Fig.1).
1).
Niewoehner concludes that important manipulative differences
existed between Neandertals and Near Eastern modern humans—differences
not in dexterity but in grip strength
…
… | Figure 1 Fossil hands of Near Eastern Mousterian humans. (Left)
Palmar view of the left hand of the Shanidar 4 Neandertal.
(Right) Palmar view of the right hand metacarpal and
phalangeal skeleton of the Qafzeh 9 early modern human The two hands
are not to (more ...) |
The small joints between the bones of the hand must withstand
both violent forces (such as impact forces from striking a hammerstone
on a flint core) and repetitive loading. For these reasons, articular
cartilage in the wrist and hand is prone to degeneration, and
osteoarthritis is found often in the hands of foraging people (7, 8).
The debilitating pain of osteoarthritis and reduced mobility of the
thumb and fingers certainly would have interfered with an individual's
ability to manufacture tools and procure edible resources. The
associated reduction in fitness creates selection for joint
configurations that best limit damaging forces in the context of
commonly used grips and manipulative activities. For these reasons, the
results reported by Niewoehner are likely to reflect real and
meaningful differences in manipulation between groups. But what is
the significance of these differences?
Living humans commonly use oblique power grips when using tools
set in handles. Hafting of lithic tools into wooden or bone handles was
likely a part of the technological repertoire of early modern humans.
Mastic (gum) was used as a hafting adhesive during the Middle
Paleolithic at Apollo 11 Cave in Namibia (9), which is precisely the
region of the world in which modern human anatomy and many aspects of
modern behavior are thought to have arisen first (10). However, hafting
seems to have been part of the Neandertal repertoire as well. Haft
polish has been observed on lithics from the European Mousterian
(before the arrival of modern humans; ref. 11), and solidified pieces
of resin bearing imprints of the stone tools and wooden hafts have been
recovered from the Mousterian of Germany (12). Shea (13) also reported
edge wear attributable to hafting in roughly equal frequencies on
Mousterian lithics from Kebara (with associated Neandertal fossils) and
Qafzeh (with associated modern human fossils) caves in Israel (some
of what is identified as haft wear, however, may be the result of
prehension with gritty fingers, and thus differences in the frequency
of hafting still may have existed between groups). What may have
differed between these groups then was not the ability to produce
composite tools but rather the importance of this technology. Given the
increased mechanical advantage of hafted over hand-held tools in
butchery, wood working, hide preparation, and other tasks, such a
difference may reflect contrasts in the relative amount of muscular
effort that each group devoted to economic and technological
activities. A more profitable use of leverage by the
Skhūl/Qafzeh modern humans would be consistent with aspects of
their upper-limb morphology that denote reduced mechanical loads
relative to, and arm positions different from, the Neandertals (4, 14).
Hafting seems to have been relatively common during Mousterian
times in the Near East. Traces of bitumen adhesive on tools from Hummal
and Umm El Tlel (Syria; ref. 15), as well as the recovery of a
broken Levallois point embedded in a cervical vertebra of a wild ass at
Umm El Tlel (16) and the edge wear analyses reported by Shea, attest to
a level of reliance on hafted tools sufficient to have made this
behavior archeologically visible. Unfortunately, without direct
evidence in the form of human fossils, we cannot know which group left
these remains, and evaluating the importance of hafting in the two
groups remains difficult.
Two indirect lines of archeological evidence hint that hafting
may have played a more important role in the economic and technological
realms of early modern humans in the Levant. Although wear attributed
to hafting occurs with equal frequency at Kebara and Qafzeh (13), there
is a marked contrast between the sites in the extent of retouch on the
used tools. Only about 20% of the used tools from Kebara exhibited
retouch, compared with 64% of those from Qafzeh (13). Sharpening
retouch is to be expected with hafted tools, because it's easier
usually to resharpen an edge than to replace the lithic. However,
retouch on the tools from Qafzeh seems to have been used more to shape
the lithics than to resharpen them (13). Although the lack of
sharpening retouch remains enigmatic, the greater attention that modern
humans paid to shaping the tool initially may reflect a concern for
fitting the lithic into a prefabricated handle.
The Levallois point/lithic core ratio also has been argued to
differ systematically between Neandertal and early modern human
Mousterian sites in the Near East (17). Assuming this ratio
reflects the intensity of point production relative to
production of all tools, higher point/core ratios in
Neandertal-associated assemblages have been interpreted as
reflecting greater hunting intensity by them than by modern humans
(17). Variation in these ratios, however, can result from multiple
factors including differential loss of points from residential
sites (18). The use of foreshafts on hunting spears, for example, may
allow for the quick replacement (and discard) of damaged points in the
field, whereas points hafted directly to the spear may have been
transported more often back to camp before being removed and
discarded. This example highlights the complicating effects that
hafting and retooling can have on the archeological record
(19) and illustrates the complexity inherent in trying to interpret
behavior from lithic assemblages.
Perhaps it is just my bias as a paleontologist, but I feel
strongly that functional-morphological interpretations of Near Eastern
Mousterian human behavior, such as the work of Niewoehner (6), rest on
epistemologically firmer ground than do inferences derived from
typological and technological analyses of lithic assemblages (20, 21).
If recent suggestions (22) that Neandertals and early modern humans are
associated uniquely with different variants of the Levantine Mousterian
(Tabun B and Tabun C, respectively) can be supported, then traditional
modes of addressing variation in lithic assemblages may yet reveal
adaptive differences between groups. Until then, approaches that focus
on adaptively meaningful and generally more subtle aspects of the
lithic record, such as the work discussed above, hold more promise for
generating testable inferences about prehistoric behavior. Although
differences in retouch frequencies and point/core ratios are
admittedly weak lines of evidence for differences in the use of hafting
between groups, they do constitute archeological signatures of
behavioral differences (although we are still far from confidently
identifying those differences).
A hand better suited to oblique power grips as found by
Niewoehner (6), and a greater use of hafting, are not in themselves
adaptive innovations sufficient to have given modern humans a
competitive edge over indigenous archaic populations. Rather, these
differences are likely part of an emerging modern human adaptive
system that involved greater use of task-specific tools, more
complex composite tools, greater planning depth and logistical
complexity to foraging, and increased social complexity (10).