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Brief communication The distribution of perikymata on Qafzeh anterior teeth.

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AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 141:152–157 (2010)
Brief Communication: The Distribution of Perikymata
on Qafzeh Anterior Teeth
Debbie Guatelli-Steinberg1* and Donald J. Reid2
1
Department of Anthropology, The Ohio State University, Columbus, OH 43210
Department of Oral Biology, School of Dental Sciences, University of Newcastle upon Tyne,
Newcastle upon Tyne NE2 4BW, UK
2
KEY WORDS
modern humans; Neandertals; enamel
ABSTRACT
Recent studies have suggested that
Neandertals and modern humans differ in the distribution of perikymata (enamel growth increments) over
their permanent anterior tooth crowns. In modern
humans, perikymata become increasingly more compact
toward the cervix than they do in Neandertals. Previous
studies have suggested that a more homogeneous distribution of perikymata, like that of Neandertals, characterizes the anterior teeth of Homo heidelbergensis and
Homo erectus as well. Here, we investigated whether
Qafzeh anterior teeth (N 5 14) differ from those of modern southern Africans, northern Europeans, and Alaskans (N 5 47–74 depending on tooth type) in the percentage of perikymata present in their cervical halves.
Using the normally distributed modern human values
for each tooth type, we calculated Z-scores for the 14
Qafzeh teeth. All but two of the 14 Qafzeh teeth had
negative Z-scores, meaning that values equal to these
would be found in the bottom 50% of the modern human
samples. Seven of the 14 would be found in the lowest
5% of the modern human distribution. Qafzeh teeth
therefore appear to differ from those of modern humans
in the same direction that Neandertals do: with generally lower percentages of perikymata in their cervical
regions. The similarity between them appears to represent the retention of a perikymata distribution pattern
present in earlier members of the genus Homo, but not
generally characteristic of modern humans from diverse
regions of the world. Am J Phys Anthropol 141:152–157,
2010. V 2009 Wiley-Liss, Inc.
The presence of perikymata on the enamel surfaces of
teeth has enabled researchers to investigate differences
in enamel formation time among fossil hominins, with
potential implications for differences in the paces of their
life histories (e.g., Dean et al., 2001). Perikymata are
external manifestations of internal growth increments
(striae of Retzius) present on the surface of lateral
enamel (enamel on the sides of teeth). In the cuspal
region of teeth, striae of Retzius cover each other in a series of domes and do not emerge as perikymata onto the
enamel surface. Cuspal enamel formation time therefore
represents an unknown portion of enamel formation
time in most studies of fossil teeth. Research on fossil
enamel formation has tended to focus on anterior as
opposed to posterior teeth, because cuspal enamel is
known (from histological studies) to represent a relatively small portion of overall enamel formation time in
anterior teeth (10% as opposed to 30–35% in posterior
teeth; Reid and Dean, 2006).
Although the connection between anterior tooth
enamel formation time and life history has been questioned (e.g., Guatelli-Steinberg, 2009), studies of perikymata in anterior teeth have revealed apparent enamel
growth pattern differences among fossil hominins (Dean
and Reid, 2001; Ramirez-Rozzi and Bermúdez de Castro,
2004; Guatelli-Steinberg et al., 2005). Dean and Reid
(2001) found that Paranthropus tends to have a more
uniform distribution of perikymata along the tooth
crown than does Australopithecus. In modern humans,
perikymata are usually more unevenly distributed, with
perikymata becoming increasingly more closely packed
as growth progresses from cusp to cervix (but dropping
off in density in the last (cervical) decile of growth).
Although Dean and Reid (2001) found that the distribu-
tion of perikymata in OH 7 (Homo habilis) is similar to
that of modern humans, they noted that a relatively
more uniform distribution of perikymata characterizes
KNM ER 1590 (Homo rudolfensis), KNM WT 15000
(Homo ergaster), and Sangiran 4 (Homo erectus). Interestingly, H. heidelbergensis as well as Neandertals also
have a more homogeneous distribution of perikymata
than either Upper Paleolithic/Mesolithic modern humans
(Ramirez-Rozzi and Bermúdez de Castro, 2004) or more
recent modern humans from diverse regions of the world
(Guatelli-Steinberg et al., 2007). Thus, with the exception of OH 7, a more uniform distribution of perikymata
appears to have characterized the genus Homo prior to
the evolution of anatomically modern humans.
In all modern human teeth studied thus far, there
appears to be a slowing of enamel formation in the cervical relative to incisal half of the tooth, as assessed from
either the distribution of striae of Retzius in histological
sections or from the distribution of perikymata on
enamel surfaces (e.g., Reid and Dean, 2000, 2006; Ram-
C 2009
V
WILEY-LISS, INC.
C
Grant sponsor: Leakey Foundation.
*Correspondence to: Debbie Guatelli-Steinberg, Department of
Anthropology, The Ohio State University, 4034 Smith Laboratory,
174 West 18th Ave., Columbus, OH 43210, USA.
E-mail: guatelli-steinbe.1@osu.edu
Received 16 March 2009; accepted 7 July 2009
DOI 10.1002/ajpa.21158
Published online 9 November 2009 in Wiley InterScience
(www.interscience.wiley.com).
153
QAFZEH PERIKYMATA DISTRIBUTION
irez-Rozzi and Bermúdez de Castro, 2004; Guatelli-Steinberg et al., 2007). By contrast, in Neandertals, Homo
heidelbergensis, and Homo erectus, the apparent relative
slowing between the formation of enamel in the incisal
and cervical halves of surface enamel is much less pronounced, owing to a more uniform distribution of perikymata. We do not currently know if or to what extent this
apparent slowing of enamel growth along the enamel
surface from cusp to cervix results from decreases in the
rates of enamel extension and/or secretion. Furthermore,
enamel thickness as well as the course of striae of
Retzius from the enamel-dentine junction to the enamel
surface might also influence perikymata distribution.
Surface curvature differences between Neandertals and
modern humans, however, do not appear to be responsible for differences in the distribution of perikymata over
their enamel surfaces (Guatelli-Steinberg et al., 2007).
In this article, we investigate the perikymata distribution of a sample of teeth from the 90- to 100,000-year-old
site (Schwarcz et al., 1988; McDermott et al., 1993) of
Qafzeh in southwest Asia. In their cranial and skeletal
features, these specimens show an overall pattern of
‘‘derived modern human features with a minority of
retained archaic features’’ (Trinkaus, 2006). Schillaci
(2008) found that his sample of early anatomically modern humans from southwest Asia had slightly closer
morphometric similarities to Neandertals than to Upper
Paleolithic modern Europeans. He suggested that this
result could reflect a slightly more recent common ancestry between Neandertals and early modern humans from
southwest Asia or gene flow between them.
Given that the Qafzeh hominins appear to be archaic
in some ways, we wondered how different they are from
modern humans in their distribution of perikymata.
Monge et al. (2006) found that Qafzeh 4 and 10 were
more similar to nonmodern hominins in their perikymata packing patterns than to the modern human sample in Dean and Reid (2001). To further investigate this
question, we compared Qafzeh specimens to modern
humans from Alaska (Inupiaq), southern Africa, and
northern Europe in terms of the percentage of perikymata present in the cervical halves of each of six anterior tooth types. Guatelli-Steinberg et al. (2007) found
that for each anterior tooth type, the average percentage
of perikymata in the cervical halves of Neandertal teeth
was lower than the lowest average percentage found in
any of the modern human tooth types. In Neandertals,
average percentages ranged from 58.4% (UI1) to 62.4%
(LI2) while in the modern human samples, averages
ranged from 64.1% (southern African UI1 and Northern
European UC) to 68.5% (Inupiaq UI2). Neandertals and
modern humans were found to be statistically significantly different for the percentage of perikymata in the
cervical halves of their teeth in 16 of 18 Bonferroni-corrected t-tests for Neandertals versus modern humans. In
the present study, we hypothesized that if the Qafzeh
teeth were more archaic in their distribution of perikymata, then they, like Neandertals, would exhibit lower
percentages of perikymata in the cervical halves of their
teeth when compared to the teeth of modern humans.
MATERIALS AND METHODS
The southern Africa and northern European samples
consist of histological sections; the Alaskan (Inupiaq),
Neandertal, and Qafzeh samples consist of labial surface
replicas. Histological preparation and replica-making
TABLE 1. Sample sizes for modern human
and Neandertal teeth
Tooth
type
UI1
UI2
UC
LI1
LI2
LC
Southern
African
Northern
European
Alaskan
Inupiaq
Neandertal
20
21
26
20
23
24
19
16
39
15
13
13
10
10
9
12
14
10
9
9
14
4
7
9
materials and techniques are given in Reid and Dean
(2000, 2006) and Guatelli-Steinberg et al. (2005, 2007),
respectively. The modern human (Inupiaq, Northern European, and Southern European) samples used in the
present study are identical to those detailed in GuatelliSteinberg et al. (2007). (In this study, we use the more
accurate term ‘‘Inupiaq’’ rather than ‘‘Inuit’’ for the Alaskan sample.) The Neandertal sample used in this study
differs in two ways from that described in Guatelli-Steinberg et al. (2007): 1) Krapina 194 is not included, as it is
an antimere of Krapina 195 (Radovčić et al., 1988), and
2) Tabun 2 is not included because some contend it is
modern human (Rak, 1998) although others maintain
that the mandible manifests a combination of ancestral
and Neandertal features (Stefan and Trinkaus, 1998).
Table 1 gives sample sizes by tooth type for modern
humans and Neandertals. Table 2 lists the Qafzeh specimens. For all samples, only one tooth (right or left) was
used from each individual per tooth type. Choice of right
or left was made on the basis of which antimere was
most complete. Only teeth estimated to have 80% or
more of their crown heights intact were selected for
analysis. For replicas, crown heights were reconstructed
under a Wild stereomicroscope using a graticule with 10
major divisions and 10 minor divisions. The lowest point
of the CEJ was ascertained and the first unit on the
graticule was placed there. Magnification was set so that
the projected crown height in a worn tooth replica was
placed at the 10th major division line of the graticule.
The percentage of the projected crown height represented by the actual tooth face was then read from the
graticule. Crown height projections were based on crown
morphology. In canine teeth, crown height projections
were made by following the contour of each side of the
tooth cusp and projecting it until the sides met. Projections of crown height for incisor teeth were based on the
morphology of more complete incisor crowns from each
population sample. All histological sections of teeth were
photographed using a Zeiss Universal microscope with a
1.53 objective and then montaged in Adobe Photoshop
to give a full image of the tooth. When sections of teeth
demonstrated attrition, they were superimposed over
same size images of unworn teeth in Adobe Photoshop to
gauge the amount of crown height lost. Guatelli-Steinberg et al. (2007) conducted additional analyses on samples limited to teeth with 90 or 95% of their estimated
crown heights intact. Analyses of these restricted samples with more complete crowns yielded very similar
results to analyses based on the more inclusive sample
consisting of teeth with 80% or more of their estimated
crown heights present. Thus, for the present study, the
larger and more inclusive samples of Neandertal and
modern human anterior teeth were used.
Perikymata were counted under a Wild stereomicroscope using a magnification of 503. Each replica was oriAmerican Journal of Physical Anthropology
154
D. GUATELLI-STEINBERG AND D.J. REID
TABLE 2. Perikymata counts on Qafzeh specimens
Tooth
type
UI1
UI2
UC
LI1
LI2
LC
Specimen
Qafzeh
Qafzeh
Qafzeh
Qafzeh
Qafzeh
Qafzeh
Qafzeh
Qafzeh
Qafzeh
Qafzeh
Qafzeh
Qafzeh
Qafzeh
Qafzeh
4e
10
12
15
11
15
11
9
11
15
9
11
15
11
MCHb
(mm.)
RCHc
(mm.)
Perikymata counts per decile numbered 1 (incisal)–10 (cervical)d
a
1
2
3
4
5
6
7
8
9
20
Total
Pk
ULI1
URI1
*ULI1
URI1
ULI2
URI2
ULC
LLI1
LRI1
LLI1
LLI2
LRI2
LLI2
LLC
12.7
12.5
11.75
12.0
9.75
10.1
10.6
10.55
7.3
10.1
11.5
8.45
10.0
9.8
12.7
12.5
12.4
12.1
10.5
11.12
12.0
11.5
9.0
10.1
11.5
9.6
10.0
11.2
7
7
11
10
9
9
8
9
9
9
9
8
9
8
8
8
12
10
9
10
10
10
9
9
10
9
9
9
9
9
12
10
10
10
12
12
8
9
12
8
9
12
9
10
12
11
11
10
12
13
8
10
12
8
12
12
10
10
12
13
11
11
12
14
9
9
12
11
11
12
14
14
13
14
13
13
13
16
10
12
13
12
11
13
13
15
14
13
13
13
15
16
10
14
16
13
12
13
15
18
17
18
15
15
21
16
11
14
19
14
17
17
18
19
20
18
17
17
20
22
15
16
22
14
17
20
24
23
21
21
17
19
20
22
17
20
23
18
18
20
127
133
144
138
125
127
143
150
106
122
148
115
125
136
Tooth
a
Asterisk denotes a tooth (Qafzeh 12 ULI1) that had not yet completed crown formation, but which appeared to be 95% complete.
Measured crown height.
Reconstructed crown height.
d
Italicized perikymata counts are estimates. For deciles 1 and 2, these are based on averages from other teeth of the same tooth
type for which it was possible to count perikymata in these deciles. (In some cases, these averages are based not only on the data
in this table, but also on data from teeth that were ultimately not included in the sample either because they were antimeres of
these teeth or because perikymata could not be counted over several other deciles.) The estimate for decile 10 in the Qafzeh ULI1 is
based on a partial count within the half-completed deciles of this tooth, which was estimated to have completed 95% of its full
crown height.
e
Data from the Qafzeh 4 ULI1 are from Monge et al. (2006).
b
c
ented orthogonally to the microscope’s optical axis. In
the northern European and southern African samples,
striae of Retzius were counted under transmitted light
microscopy (for sample preparation, see Reid and Dean,
2000, 2006). Only striae clearly outcropping onto the surface as perikymata were counted. For this reason, we
refer to the striae counts in our histological samples as
perikymata counts. Each tooth was divided into deciles
of reconstructed crown height numbered from decile 1 at
the either present or projected cusp tip/incisal edge to
decile 10 at the cervix. Perikymata were counted within
each decile. For teeth missing up to 20% of their crowns
owing to wear, estimates of perikymata were made for
the first two deciles. Perikymata counts within the first
two deciles of complete crowns have very low standard
deviations, ranging from one to two perikymata for each
tooth type within each population (Guatelli-Steinberg et
al., 2007). Low variation within the first two deciles of
growth makes it possible to accurately estimate growth
in minimally worn teeth based on average perikymata
counts in the first and second deciles of complete crowns
per tooth type and population sample. Teeth were
excluded from the study if more than one additional decile (beyond the first two deciles) contained indistinct
perikymata. For teeth in which this single additional
decile contained indistinct perikymata, counts were estimated by interpolating from adjacent deciles (Dean and
Reid, 2001). To eliminate interobserver error, only counts
made by D.J.R., whose error in counting perikymata is
less than 5% (Dean et al., 2001), were used.
Any crowns that had not yet completed growth (i.e.,
with missing CEJs) were excluded from all Neandertal
and modern human samples. However, because the set
of available Qafzeh teeth is so small, we included a single Qafzeh specimen, the upper left incisor of Qafzeh 12
that had not yet completed its growth, but appeared to
be 95% complete. In this one specimen, an estimate of
the perikymata in the cervical decile was made on the
American Journal of Physical Anthropology
basis of the number of perikymata present in the halfdecile that was present. However, because the number of
perikymata in cervical deciles is so variable, we report
our results both with and without this specimen
included. We also include published data by Monge et al.
(2006) on the Qafzeh 4 ULI1, a specimen we were unable
to observe. We do not know if our counts systematically
differ from those of Monge et al.; however, our total
counts of perikymata on Qafzeh 10 URI1 differ by only
two perikymata: Monge et al. counted 131 perikymata
for this specimen while D.J.R. counted 133.
Our sample of Qafzeh teeth is more inclusive than
that of Monge et al. (2006), who employed more conservative criteria for sample inclusion than we did. Monge et
al. (2006) did not include the teeth of Qafzeh 12 owing to
its skeletal pathologies. We included the Qafzeh 12 ULI1
because it was nearly complete. We did not observe any
obvious enamel hypoplasia on this tooth or any of the
other incomplete teeth of Qafzeh 12 teeth (there were
accentuated perikymata near the cervix of the ULI1),
such that while this individual’s skeletal growth was
pathological, its enamel growth appeared normal. We
also include some teeth from Qafzeh 11 and Qafzeh 15,
which Monge et al. (2006) found to lack perikymata over
portions of their surfaces. We were able to obtain perikymata counts from some of the teeth of these individuals
and therefore we include them in our sample. Monge et
al. (2006) stated that even minimal surface wear ‘‘limits
the ability to make accurate counts even on surfaces
that retain some measure of perikymata structure’’
(2006:28). We find, however, that perikymata grooves
can often be discerned on teeth with some surface wear.
When perikymata grooves were indistinct within a decile, we considered that decile to have unobservable perikymata. As described above, we used minimal and controlled estimates for such areas and applied our criteria
for sample inclusion consistently across all specimens.
For these reasons, we report data for a larger sample of
155
QAFZEH PERIKYMATA DISTRIBUTION
Fig. 1. Means for the percentage of perikymata in the cervical halves of anterior teeth for each population sample are shown in
(a). In (b), the means and confidence intervals are shown for the combined modern human and Neandertal samples, with individual
data points for the Qafzeh specimens superimposed.
Qafzeh teeth than did Monge et al. (2006). In all, as can
be seen in Table 2, estimates were made for 11 of 140 of
the Qafzeh specimens’ deciles, and in 10 of the 11 cases,
these were in the incisal deciles of the tooth, where perikymata numbers are low and least variable.
To investigate potential growth differences among population samples, teeth were compared in the percentages
of their total number of perikymata present in their cervical halves. Because the Qafzeh sample sizes are small,
we were unable to perform statistical tests of sample
means. Instead, for each Qafzeh tooth, we determined
the probability of drawing its value for the percentage of
perikymata in its cervical half from the combined modern human sample distribution. To assess these probabilities, we created a combined modern human sample (consisting of the northern European, southern African, and
Inupiaq subsamples) for each tooth type. Next, we used
D’Agostino’s Pearson K2 test in SAS 9.1 to test whether
the combined modern human samples for each tooth
type were normally distributed with respect to the percentage of perikymata in the cervical halves of teeth. K2
values less than 5.991 (chi-square with two degrees of
freedom, P [ 0.05) represent distributions that do not
deviate significantly from normality. Once the normality
of these samples was assessed, we calculated Z-scores
and associated probabilities, based on the modern
human distributions, for the percentages of perikymata
in the cervical halves of the Qafzeh specimens.
RESULTS
Table 2 presents the perikymata counts per decile for
the Qafzeh specimens. Values in italics are estimates
and the asterisk denotes the incomplete Qafzeh 12 ULI1.
Figure 1a plots the mean percentages of perikymata in
the cervical halves of teeth per tooth type for all population samples. Figure 1b plots the means and 95% confidence intervals for the Neandertal and the combined
modern human samples, with the Qafzeh teeth plotted
as individual data points. Neandertal means can be seen
to fall below modern human means (as reported in Guatelli-Steinberg et al., 2007). Means for the different Qaf-
TABLE 3. Mean percentages of perikymata on combined modern
human samples by tooth type, with standard deviation and
D’Agostino’s Pearson K2 statistic for normality
Mean percentage
of perikymata
Standard
Tooth Sample
in cervical
deviation
K2
half of tooth
of mean statistic P-value
type
size
UI1
UI2
UC
LI1
LI2
LC
49
47
74
47
50
47
65.5
65.9
64.8
66.04
66.1
65.4
3.7
3.4
3.2
2.6
3.2
3.2
2.21
0.50
4.32
1.54
2.87
3.16
0.331
0.779
0.115
0.463
0.238
0.206
K2 values less than 5.991 (chi-square, P [ 0.05) indicate distributions for which normality could not be rejected.
zeh tooth types also generally appear to fall below those
for modern humans, but the small sizes of the Qafzeh
samples preclude tests for mean differences between
them and the modern human samples.
To calculate Z-scores for each of the Qafzeh specimens
based on the modern human samples, we first established that the combined modern human samples per
tooth type were normally distributed. Table 3 gives sample sizes, means, standard deviations, and D’Agostino’s
Pearson K2 test statistic for each of the modern human
tooth type samples. Because all values for D’Agostino’s
Pearson K2 test statistic were lower than the cut-off
value of 5.991, normality could not be rejected.
Z-scores for each of the Qafzeh specimens and associated probabilities are given in Table 4. All but two of the
14 Qafzeh teeth have negative Z-scores, meaning that
values equal to these would be found in the lower 50% of
the modern human sample distribution. Of the 14 teeth
including the ULI1 of Qafzeh 12, seven would be found
in the lowest 5% of the modern human distribution.
These seven teeth come from three of the six individuals
represented in this sample. Of the 13 total teeth not
including the ULI1 of Qafzeh 12, six would be found in
the lowest 5% of the modern human distribution. These
six teeth come from two of five individuals.
American Journal of Physical Anthropology
156
D. GUATELLI-STEINBERG AND D.J. REID
TABLE 4. Percentages of perikymata in the cervical halves of Qafzeh teeth
Tooth
type
UI1
UI2
UC
LI1
LI2
LC
Qafzeh
individual
Qafzeh
Qafzeh
Qafzeh
Qafzeh
Qafzeh
Qafzeh
Qafzeh
Qafzeh
Qafzeh
Qafzeh
Qafzeh
Qafzeh
Qafzeh
Qafzeh
c
4
10
12
15
11
15
11
9
11
15
9
11
15
11
Qafzeh
tootha
Percentage of perikymata
in the cervical halves
of Qafzeh specimens
ULI1
URI1
*ULI1
URI1
ULI2
URI2
ULC
LLI1
LRI1
LLI1
LLI2
LLI2
LRI2
LLC
66.1
66.9
59.03
60.9
60.0
60.6
62.2
61.3
59.4
62.3
61.3
60.0
62.5
60.1
Mean percentage of perikymata
in cervical half of tooth
(and standard deviation) for
combined modern human sample
65.5
65.5
65.5
65.5
65.9
65.9
64.8
66.0
66.0
66.0
66.1
66.1
66.1
65.4
(3.7)
(3.7)
(3.7)
(3.7)
(3.4)
(3.4)
(3.2)
(2.6)
(2.6)
(2.6)
(3.2)
(3.2)
(3.2)
(3.2)
Z score
P-valueb
0.163
0.380
21.74
21.24
21.72
21.54
20.81
21.81
22.54
21.43
21.82
22.08
21.15
21.65
0.435
0.352
0.041
0.108
0.043
0.062
0.210
0.034
0.006
0.076
0.034
0.020
0.125
0.050
Z-scores and probabilities based on the combined modern human distributions.
a
Asterisk denotes tooth that had not yet completed crown formation.
b
P-values 0.05 or less are in boldface.
c
Data from the Qafzeh 4 ULI1 are from Monge et al. (2006).
Fig. 2. From left to right: SEM montage of Neandertal LLI2 (Krapina 90), Qafzeh LLI2 (Qafezh 15), and Inupiaq LLI2 (99.1411). All teeth were imaged at a magnification of 203, with an accelerating voltage of 5.0 keV and spot size of 4.The Qafzeh LLI2
was imaged with a tilt angle of 30 degrees in order to enhance contrast.
DISCUSSION AND CONCLUSIONS
The purpose of this study was to investigate whether
Qafzeh teeth are different from those of modern humans
in the percentage of perikymata present in their cervical
American Journal of Physical Anthropology
halves. Although some of the Qafzeh teeth do not differ
significantly from modern humans in this respect, most
appear to fall in the lower 50% of the modern human
distribution, and a few fall within the lowest 5% of the
distribution. Thus, this sample of Qafzeh teeth appears
QAFZEH PERIKYMATA DISTRIBUTION
to differ from those of modern humans in the same direction that Neandertals do: with generally lower percentages of perikymata in their cervical regions. As can be
seen in the SEM montages in Figure 2, perikymata
become much more closely spaced in the cervical relative
to incisal halves of the Inupiaq LI2 than they do in either the Neandertal or Qafzeh LI2s. Although sample
sizes precluded a similar test between the Qafzeh and
Neandertal teeth, plots of the averages for these teeth
(Fig. 1a,b) reveal the similarity of the Qafzeh and Neandertal teeth, particularly for the UI2, LC, LI2, and LC.
Values for two of the Qafzeh UI1s and a single UC are
closer to the modern human than Neandertal means for
these tooth types, revealing overlap in the ranges of values, as is also true for Neandertals and modern humans
(Guatelli-Steinberg et al., 2007).
As mentioned, differences in enamel extension rates,
secretion rates, enamel thickness, and/or the paths of
striae of Retzius may be responsible for different perikymata distribution patterns. Moreover, it is clearly possible that similar perikymata distribution patterns could
be produced by different combinations of these variables.
Since we cannot section the Qafzeh, Neandertal, and
Inupiaq teeth, we do not know which factors are
involved in these groups. We are currently studying our
histological sections of northern European and southern
African modern human teeth to determine if similar
enamel growth processes underlie these perikymata distribution patterns. Our preliminary analysis suggests
that in both southern African and northern European
teeth, those with greater percentages of perikymata in
their cervical halves tend to also have larger differences
in average enamel extension rates associated with
incisal versus cervical halves of the crown. However, we
have not yet determined to what extent other factors
(variation in secretion rates, enamel thickness, and/or
the path of striae of Retzius) might also be contributing
to variation in the distribution of perikymata in northern European and southern African teeth.
Although there is currently insufficient evidence to
suggest that the modern human perikymata distribution
pattern identified here is a synapomorphy of all modern
human populations, this pattern is often lacking in earlier members of the genus Homo, including, it seems, in
many of the teeth from Qafzeh. The Qafzeh hominins
may represent an early dispersal of humans out of Africa
and exhibit several archaic features (Schillaci, 2008).
The more uniform perikymata distribution of the Qafzeh
hominins adds to their list of archaic features.
ACKNOWLEDGMENTS
The authors thank Yoel Rak and Alon Barash at Tel
Aviv University for access to the Qafzeh specimens in
157
their care. They thank Paul Sciulli at The Ohio State
University for his statistical advice and Jules Angel for
her help with images. They also greatly appreciate the
helpful comments of the reviewers, Associate Editor, and
Editor.
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