, 1443 (2007); 318
Charles A. Lockwood,
Extended Male Growth in a Fossil Hominin Species
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imation would predict a divergent susceptibility
(Fig. 3A). By using Eq. 1 to define an effective
superfluid density from the zero field response,
(Fig. 3B) that fluctuations make the suscepti-
bility deviate from the mean field response below
Tc(0), gradually smoothing the transition. Our pa-
rameterization of the theory shows that g is the
only sample-dependent parameter at T = Tc(0).
The temperature range where non-Gaussian
fluctuations are important is typically param-
eterized through the Ginzburg parameter as
the magnitude of the response. Far above this
range, Gaussian fluctuations dominate, and the
susceptibility is a function of jT − Tcð0Þj=Ec∝
The theory’s dependence on g allows us to
state the criterion for the visibility of the Little-
Parks effect in the context of fluctuations. The
region that is shaded in green in Fig. 3C is
above Tc(F0/2) because x(T) > 2R. The sus-
ceptibility would be zero in this regime if
fluctuation effects were not considered. When
g ≪ 1, the distinct Little-Parks shape is visible
in that the susceptibility is smaller at Fa= F0/2
than at Fa= 0. However, when g ≫ 1, the
Little-Parks shape is entirely washed out by
fluctuations (Fig. 4). For sufficiently large g, the
eff¼ ðm0L=wdÞ∂I=∂FajFa¼ 0, one can see
susceptibilities at F = 0 and F0/2 are equal and
opposite even below Tc(Fa= F0/2), so the re-
sponse appears sinusoidal. This dependence on
g, rather than L and x(T) alone, is the reason
why the Little-Parks line shape does not occur
in the ring shown in Figs. 2A and 4C.
Several factors contribute to the large fluc-
tuation response near Fa= F0/2 above Tc(Fa).
First, the Gaussian fluctuations between Tc(Fa=
0) and Tc(Fa) have a large magnitude, which is
due to the interplay between adjacent phase
fluctuation region in Fig. 3C is small.Thus, there
is a large region where the magnitude of the
persistent current near Fa= F0/2 is strictly a
Gaussian fluctuations play an increased role in
the phase diagram, and multiple phase winding
modes need to be considered (13), indicating the
importance of phase fluctuations. In all rings,
nonhomogeneous wave functions may have a
nonnegligible contribution to the final currents
Small variations in width (SOM text) make non-
homogeneous wave functions more important
(14) and would be important to include in an
Fluctuation effects play a important role in
1D superconducting structures. Our analysis
explicitly demonstrates how Gaussian and non-
Gaussian fluctuations affect the persistent cur-
rent in rings with various diameters and cross
sections, as a function of applied magnetic flux.
A single parameter, g, characterizes the fluctua-
tions for a given ratio of the temperature-
dependent coherence length to the circumference.
When g is large, the signature of a Little-Parks
flux-dependent Tc(Fa) is entirely washed out by
fluctuations. When g is small, the susceptibility
in the non-Gaussian region near Tc(Fa) is en-
hanced, and Gaussian fluctuations are clearly
visible between Tc(Fa) and Tc(0) for Fa≈ F0/2.
This new framework for understanding Little-
Parks fluctuations is supported by our data on
fluctuation-induced currents in rings.
References and Notes
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material on Science Online.
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14. J. Berger, J. Rubinstein, Phys. Rev. Lett. 75, 320 (1995).
15. We acknowledge support from the Packard Foundation
and NSF grants no. DMR-0507931, DMR-0216470,
ECS-0210877, ECS-9731293, and PHY-0425897.
We thank J. Price, Y. Imry, M. R. Beasley, Y. Oreg, and
especially G. Schwiete for helpful discussions and
A. Bachar for the illustration in Fig. 1B.
Supporting Online Material
Materials and Methods
Tables S1 and S2
3 August 2007; accepted 16 October 2007
Extended Male Growth in a Fossil
Charles A. Lockwood,1,2* Colin G. Menter,3Jacopo Moggi-Cecchi,2,4Andre W. Keyser2
In primates that are highly sexually dimorphic, males often reach maturity later than females, and
young adult males do not show the size, morphology, and coloration of mature males. Here we
describe extended male development in a hominin species, Paranthropus robustus. Ranking a large
sample of facial remains on the basis of dental wear stages reveals a difference in size and
robusticity between young adult and old adult males. Combined with estimates of sexual
dimorphism, this pattern suggests that male reproductive strategy focused on monopolizing
groups of females, in a manner similar to that of silverback gorillas. However, males appear to
have borne a substantial cost in the form of high rates of predation.
such it is routinely analyzed and debated when
seen in extinct hominin species (1–6). The ex-
pectation is that higher levels of sexual dimor-
phism correlate with higher levels of male-male
competition and social systems in which males
control mating access to multiple females (7).
exual dimorphism is the only direct skeletal
evidence available for reconstructing the
evolution of human social behavior, and as
However, partly due to the limitations of small
fossil samples, estimates of dimorphism have led
to divergent inferences about social behavior in
fossil hominins, ranging from monogamous to
highly polygynous groups. Here we combine
analysis of dimorphism with anotheraspectoflife
the timing of maturity (8)—and use the results to
reconstruct social behavior.
Applied Flux (Φ0)
Fig. 4. Mean field theory (green), fluctuation
with different g parameters. The mean field
response is derived from the fluctuation theory
shape is clearly observable. (B) T = 1.25 K.When
g ≈ 1, the reduction of the response due to the
Little-Parks effect is significantly suppressed. (C)
is completely washed out by fluctuations, which
affect the responses at all flux values.
γ = 0.074
γ = 0.6
γ = 13
VOL 31830 NOVEMBER 2007
on December 3, 2007
We focus on Paranthropus robustus, a South
African robust australopithecine, because there are
a large number of specimens available (35 were
from the Swartkrans site, Kromdraai, and recent
finds from Drimolen (9, 10). The P. robustus
deposits at these sites have been dated to 1.5 to 2.0
to relative age among adults, we only considered
individuals with (i) M3 erupted, (ii) sufficient parts
and (iii) postcanine teeth well enough preserved to
determine age from the relative degree of tooth
face or maxilla, 17 of which are from Swartkrans,
and 1 each from Drimolen and Kromdraai. For
10 are from Swartkrans, 5 from Drimolen, and
1 from Kromdraai (Table 1). Because many spec-
imens are fragmentary, we determined a non-
parametric ranking of individuals based on overall
sizeratherthan a specific measurement (13). Age
ranks were determined on the basis of tooth wear
of the postcanine row, following generally ac-
cepted methods (13, 14). The sample represents
nearly every stage of dental wear from young
adulthood to old age (15).
From this analysis, we infer that maximum
(presumably male) size was greater among old
adultsthan youngadults(Fig.1).Oldadultsin the
morphology with respect to features diagnostic of
eny of sexual dimorphism in modern primates
(17), we interpret this pattern as continued growth
in males between early skeletal adulthood and full
throughout the age range. For example, SK 21 is
the oldest specimen in the sample of maxillas, but
also the smallest. Because small, relatively gracile
individuals occur at every age, we conclude that
females have reached full skeletal size by the time
M3 has erupted or soon thereafter.
Extended male growth occurs in primates
when male reproductive success is concentrated
in a period of dominance resulting from intense
male-male competition (17, 18). Climbing the
dominance hierarchy typically involves not only
an increase in size but also changes in soft-tissue
the likelihood of success is greatest (17, 19, 20).
In primates showing bimaturism, sexual di-
morphism in the eruption of the last permanent
tooth (M3 or the canine) is clearly less than the
emergence at similar times (21, 22), but gorilla
male growth in body mass continues for years
(17), and male gorillas do not become socially
adult until as much as 5 or 6 years after females
(23). In a more extreme case, eruption of the
permanent teeth in mandrills is completed in
males before females (24), but males continue to
grow in body mass and body length for several
years (25). Differences between dentally mature
thus well-recognized in modern primates.
has been aided by the discovery of DNH 7, a
complete skull from Drimolen (9, 10). It is sub-
stantially smaller than the well-preserved skulls
of P. robustus from Swartkrans (such as SK 12,
SK 46, SK 48, and SK 83) and Kromdraai (TM
1517) (table S1). Differences between DNH 7
and larger individuals are consistent with those
expected between females and males. For ex-
ample, the larger individuals have sagittal crests
reaching onto the frontal bone, as well as deeply
projecting mastoid processes, whereas DNH 7
lacks a sagittal crest and has reduced mastoid
regions. The degree of size difference between
DNH 7 and larger, presumably male specimens
can be explained by a gorillalike level of sexual
dimorphism but not the lower levels of dimor-
phism seen in chimpanzees and modern humans
(supporting online material). Furthermore, it is
unlikely that any of the other relatively complete
skulls are female. In comparison to extant hom-
inoids, the difference between even the smallest
of the previously known crania (TM 1517) and
DNH 7 is statistically greater than would be ex-
pected within the range of variation of females
(supporting online text and table S2). The size of
DNH 7, in combination with an understanding of
male life history, helps resolve the sex of spec-
imens such as SK 48 and TM 1517 (26, 27). The
two latter specimens are best regarded as young
skullsisalsoreflected inthe sampleofmaxillasas
a whole (28). Specimens such as SK 21, SK 821,
and SKW 8 are similar in size and proportions to
DNH 7 and are probably females (these are size
ranks 1 and 2 in Fig. 1), whereas all other speci-
mens show male size and/or morphology (sup-
porting online material). We conclude that the
maxillofacial specimens represent 4 females and
15 males overall, and 3 females and 14 males for
the Swartkrans sample only. This distribution de-
viates significantly from random sampling of an
unbiased population (using a two-tailed binomial
overall sample and P = 0.0127 for Swartkrans).
An abundance of males is perhaps not sur-
prising in a fossil sample that resulted largely
from predation. Direct evidence of carnivore ac-
tivity is present on several hominin specimens at
Swartkrans, and member 1 of this site is among
the most definitive examples of a predator-
accumulated assemblage of hominins (27, 29).
In dimorphic primates, nondominant males spend
more time alone, on the periphery of a social
group, or in small all-male bands (30). Solitary
behavior places males at risk (31, 32). For ex-
ample, when male baboons disperse, they suffer
a mortality rate at least three times as great as
that of group-living males or females (32). This
1Department of Anthropology, University College London,
Gower Street, London WC1E 6BT, UK.2Institute for Human
Evolution, University of the Witwatersrand, WITS 2050,
Johannesburg, South Africa.3Department of Anthropology
and Development Studies, University of Johannesburg, Post
Office Box 524 Auckland Park, Johannesburg, South Africa.
4Laboratori di Antropologia, Dipartimento di Biologia Animale
e Genetica,and Museo di Storia Naturale, Universitàdi Firenze,
12 via del Proconsolo, 50122 Firenze, Italy.
*To whom correspondence should be addressed. E-mail:
Table 1. Ranking of size and age (displayed in Fig. 1). Swartkrans member 1 (M1) includes all
specimens from deposits referred to as the lower bank and the hanging remnant [see (12) for
30 NOVEMBER 2007VOL 318
on December 3, 2007
degree of difference in mortality matches the
male bias at Swartkrans. Females were apparent-
ly more shielded from predation. Putting this
observation together with the conclusions about
bimaturismand sexual dimorphism,weinfer that
the distribution of food sources allowed stable
topredation pressure,and males in turnsoughtto
monopolize reproductive access to these groups
(33). If females emigrated from their natal
groups, then it is likely that they spent little time
alone and transferred directly to a male or an
established group [as occurs in gorillas (30, 34)].
The P. robustus pattern contrasts with that of
some other australopithecine collections. For ex-
ample, the sample of Australopithecus africanus is
either biased toward females or shows no bias (4).
The A. africanus accumulation from Sterkfontein
member 4 may also be the product of predator
behavior, but this conclusion is less certain than
for the Swartkrans sample (27, 35). If both
Swartkrans member 1 and Sterkfontein member
4 hominin collections are largely attributable to
carnivore activity, the difference in sex bias raises
the possibility that P. robustus and A. africanus
differed in social structure.
References and Notes
1. J. M. Plavcan, C. P. van Schaik, J. Hum. Evol. 32, 345
2. H. M. McHenry, J. Hum. Evol. 27, 77 (1994).
3. R. A. Foley, P. C. Lee, Science 243, 901 (1989).
4. C. A. Lockwood, Am. J. Phys. Anthropol. 108, 97 (1999).
5. P. L. Reno, R. S. Meindl, M. A. McCollum, C. O. Lovejoy,
Proc. Natl. Acad. Sci. U.S.A. 100, 9404 (2003).
6. We refer to differences in skull size and morphology
between males and females, which have been shown to
correlate with sexual dimorphism in body mass (36).
7. J. M. Plavcan, Yrbk. Phys. Anthropol. 116, 25 (2001).
8. Bimaturism, defined as sex differences in the timing of
cessation of growth (17).
9. A. W. Keyser, S. Afr. J. Sci. 96, 189 (2000).
10. A.W. Keyser, C.G.Menter,J. Moggi-Cecchi,T.R.Pickering,
L. R. Berger, S. Afr. J. Sci. 96, 193 (2000).
11. E. S. Vrba, in Hominid Evolution: Past, Present and Future,
P. V. Tobias, Ed. (Liss, New York, 1985), pp. 195–200.
12. C. K. Brain, in Swartkrans: A Cave's Chronicle of Early
Man, C. K. Brain, Ed. (Monograph 8, Transvaal Museum,
Pretoria, South Africa, 1993), pp. 23–33.
13. Further information on materials and methods is
available as supporting material on Science Online.
14. S. Hillson, Teeth (Cambridge Univ. Press, New York,
ed. 2, 2005).
15. In specimens with M3 recently erupted (such as SK 48,
TM 1517, and DNH 8), small dentine islands are present
on the M1s. Given schedules of dental development in
P. robustus [M1 erupted at 3 years and M3 erupted at
approximately 9 years (37)], this implies that tooth wear
on M1 began to expose dentine after 6 years. M2 erupted
approximately halfway between M1 and M3. If it
underwent comparable amounts of wear to M1, then
individuals of age rank 4 (which have exposed dentine on
M2) are at least 3 years older than those in age rank 1.
16. Y. Rak, The Australopithecine Face (Academic Press,
New York, 1983).
17. S. R. Leigh, Am. J. Phys. Anthropol. 97, 339 (1995).
18. J. M. Setchell, P. C. Lee, in Sexual Selection in Primates,
P. M. Kappeler, C. P. van Schaik, Eds. (Cambridge Univ.
Press, Cambridge, 2004), pp. 175–195.
19. P. J. Jarman, Biol. Rev. 58, 485 (1983).
20. C. H. Janson, C. P. van Schaik, in Juvenile Primates: Life
History, Development, and Behavior, M. E. Pereira,
L. A. Fairbanks, Eds. (Oxford Univ. Press, Oxford, 1993),
21. M. C. Dean, B. A. Wood, Folia Primatol. (Basel) 36, 111
22. B. H. Smith, T. L. Crummett, K. L. Brandt, Yrbk. Phys.
Anthropol. 37, 177 (1994).
23. D. P. Watts, A. E. Pusey, in Juvenile Primates: Life History,
Development, and Behavior, M. E. Pereira, L. A.
Fairbanks, Eds. (Oxford Univ. Press, Oxford, 1993),
24. J. M. Setchell, E. J. Wickings, Folia Primatol. (Basel) 75,
25. J. M. Setchell, E. J. Wickings, L. A. Knapp, Am. J. Phys.
Anthropol. 131, 498 (2006).
26. M. H. Wolpoff, in Paleoanthropology, Morphology and
Paleoecology, R. Tuttle, Ed. (Mouton, The Hague,
Netherlands, 1975), pp. 245–284.
27. C. K. Brain, The Hunters or the Hunted? An Introduction
to African Cave Taphonomy (Univ. of Chicago Press,
28. We do not assign sexes to mandibles, because they are
generally more fragmentary and there is greater overlap
in male and female mandible size in sexually dimorphic
29. K. J. Carlson, T. R. Pickering, J. Hum. Evol. 44, 431
30. A. Pusey, C. Packer, in Primate Societies, B .B. Smuts,
D. L. Cheney, R. M. Seyfarth, R. W. Wrangham, T. T.
Struhsaker, Eds. (Univ. of Chicago Press, Chicago, 1987),
31. G. Cowlishaw, Behaviour 131, 293 (1994).
32. S. C. Alberts, J. Altmann, Am. Nat. 145, 279 (1995).
33. E. H. M. Sterck, D. P. Watts, C. P. van Schaik, Behav. Ecol.
Sociobiol. 41, 291 (1997).
34. E. J. Stokes, R. J. Parnell, C. Olejniczak, Behav. Ecol.
Sociobiol. 54, 329 (2003).
35. T. R. Pickering, R. J. Clarke, J. Moggi-Cecchi, Am. J. Phys.
Anthropol. 125, 1 (2004).
36. J. M. Plavcan, J. Hum. Evol. 42, 579 (2002).
37. M. C. Dean, in Evolutionary History of the “Robust”
Australopithecines, F. E. Grine, Ed. (Aldine de Gruyter,
New York, 1988), pp. 43–53.
Fig. 1. Comparison of size ranks to age ranks for
adult maxillofacial and mandibular specimens
(Swartkrans, diamonds; Drimolen, squares; Krom-
draai, triangles). Table 1 lists the specimens used
here. The lowest age rank contains individuals
with M3 recently erupted. The largest individuals
are more advanced in age, showing at least some
dentine exposure on M2. When a randomization
test of correlation coefficients is used, age and
size are significantly correlated among the male
maxillofacial specimens (r = 0.52; P = 0.027,
one-tailed test, 5000 permutations).
Fig. 2. Size and morphological comparisons among DNH 7, SK 48, SK 12,
and SKW 12 (from left to right). They are aligned approximately on the
cementum-enamel junction of the molars, indicated by the lower line. Upper
lines indicate the level of the inferior nasal margin as a general size com-
parison. DNH 7 is the most well-preserved female specimen of P. robustus
(the mandible and cranial vault are not shown here). SK 48 is one of the
largest young adult males. SK 12 and SKW 12 are older adult males. Drawings
for SK 12 and SKW 12 are for schematic purposes only. Scale bar, 3 cm.
VOL 31830 NOVEMBER 2007
on December 3, 2007
38. This work stems from excavations at Drimolen, supported by
grants from the L. S. B. Leakey Foundation and the
Department of Science and Technology in South Africa.
Further financial support was provided to C.A.L. by the
Royal Society, UK. A.W.K. and C.G.M. thank D. and
J. Smith, on whose property Drimolen is situated, for
permission to conduct the excavation and for their assistance.
J.M.C. received support from the Italian Ministry of Foreign
Affairs (Direzione Generale per la Promozione e la
Cooperazione Culturale, ufficio V, Archaeology), and the
Italian Embassy and Italian Cultural Institute in Pretoria. We
also thank D. Shima and D. Kekane for their continued help
with the Drimolen excavation; B. Zipfel and S. Potze for
assistance with specimens; and Z. Alemseged, B. Bradley,
C. Dean, W. Kimbel, S. Leigh, M. Plavcan, J. Setchell, J. Scott,
and F. Spoor for discussion and comments.
Supporting Online Material
Tables S1 and S2
14 August 2007; accepted 24 October 2007
Boron-Toxicity Tolerance in
Barley Arising from Efflux
Tim Sutton,* Ute Baumann, Julie Hayes, Nicholas C. Collins, Bu-Jun Shi, Thorsten Schnurbusch,
Alison Hay, Gwenda Mayo, Margaret Pallotta, Mark Tester, Peter Langridge
Both limiting and toxic soil concentrations of the essential micronutrient boron represent major
limitations to crop production worldwide. We identified Bot1, a BOR1 ortholog, as the gene responsible
for the superior boron-toxicity tolerance of the Algerian barley landrace Sahara 3771 (Sahara).
Bot1 was located at the tolerance locus by high-resolution mapping. Compared to intolerant genotypes,
Saharacontains about four times as many Bot1 genecopies,produces substantially more Bot1 transcript,
and encodes a Bot1 protein with a higher capacity to provide tolerance in yeast. Bot1 transcript levels
identifiedinbarleytissuesareconsistent witharoleinlimitingthenet entryofboronintotheroot andin
the disposal of boron from leaves via hydathode guttation.
both boron deficiency and toxicity severely limit
with by using boron-tolerant varieties. Genetic
variation for boron-toxicity tolerance is knownfor
a number of crop plant species. Tolerance is most
commonly associated with the ability to maintain
low boron concentrations in the shoot (4–6). In
highly boron-tolerant Algerian landrace Sahara
of tolerance for variety improvement (4, 7). In a
cross between Sahara and the boron-intolerant
Australian malting variety Clipper, several quan-
titative trait loci (QTL) controlling tolerance were
identified (8). The major locus on chromosome
4H affects leaf symptom expression (Fig. 1A),
boron accumulation (Fig. 1B), root length re-
sponse, and dry matter production under boron-
toxic conditions (8). The ability of Sahara to
maintain lower shoot boron accumulation is at
efflux from the root (9).
We followed a map-based approach to isolate
the 4H boron-tolerance gene. Using a population
representing 6720 meioses and gene colinearity
with the syntenic region on rice chromosome 3
narrowest range between deficient and
toxic soil solution concentration (1), and
to generate markers, we delimited the tolerance
ers xBM178 and xBM162 (Fig. 2A and fig. S1)
(10). The corresponding 11.2-kb interval in rice
contains two intact copies and one 3′-truncated
version of a gene showing similarity to a family
of adenosine monophosphate (AMP)–dependent
synthetases and ligases and no other predicted
gene. Barley expressed sequence tags (ESTs)
most closely matching one of the intact copies
were used to derive the marker xBM160, which
cosegregated with the tolerance locus.
candidate genes in barley. These were barley
genes showing similarity to the Arabidopsis
NIP5;1 major intrinsic protein (11) and the
Arabidopsis BOR1 efflux transporter that is
related to bicarbonate transporters in animals
(12, 13). Both Arabidopsis genes are required for
healthy growth under conditions of low boron
supply. However, in plants the genes involved in
boron-toxicity tolerance may be related to those
shown to function in boron efficiency. Com-
parisons of barley ESTs revealed four BOR1
(At2g47160.1)–related genes. Mapping localized
boron-tolerance QTL on 4H (8). Subsequently, a
marker developed from the 3′ end of Bot1 was
found to cosegregate perfectly with the tolerance
locus in our high-resolution mapping population
(Fig. 2A), strongly suggesting that Bot1 encodes
the boron tolerance from the 4H locus. Although
barley/rice gene colinearity was found to be high
in the region (Fig. 2A), the corresponding inter-
val on rice chromosome 3 lacks a BOR1 ortholog,
and the rice gene most closely resembling Bot1
Southern hybridization with the use of a
Clipper derived Bot1 probe gave a stronger signal
in Sahara than in Clipper and other boron-
intolerant genotypes, indicating the occurrence of
additionalBot1 copies inSahara (fig.S2).Anum-
ber of restriction enzyme digests revealed hybrid-
izing Sahara fragments of mostly a single size (e.g.,
Australian Centre for Plant Functional Genomics, School of
Agriculture, Food and Wine, University of Adelaide, Waite
Campus, Private Mail Bag 1, Glen Osmond, South Australia
*To whom correspondence should be addressed. E-mail:
Fig. 1. Genetic variation for boron tolerance in barley.
(A) Boron-toxicity symptoms in leaf blades of boron-
intolerant (Clipper) and boron-tolerant (Sahara) barley
plants. Approximately eight of the oldest leaf blades from
Sahara accumulates less boron in leaf blades after
growing for 14 days in a range of solution concentrations. Data are means ± SEM (n = 3 plants).
30 NOVEMBER 2007VOL 318
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