1. These are out-of-phase lattice vibrations in the
plane of the thin sample, arising when neigh-
bouring atoms in the lattice have different
charge or mass.
Until now, lattice vibrations were something
electron microscopists have had to worry
about only in terms of the sample damage that
they induce, or when matching experimental
images to simulations7
. However, the main
point of Krivanek and colleagues’ work is that
optical phonons are key signatures of chemical
bonds, particularly those involving light ele-
ments such as hydrogen, as is well established
bythetechniquesofinfraredandRaman(opti-
cal) spectroscopy. The implication is, there-
fore, that STEM–EELS may provide a route
for the direct mapping of chemical bonding,
including that associated with light elements,
at near-atomic resolution.
Thisachievementwouldpresenttremendous
benefits in a number of highly topical areas of
research into new advanced materials and
devices. The improvements in overall energy
resolution of EELS will undoubtedly aid the
study of the local spatial variation of energy
bandgaps in semiconducting structures, and
the identification of localized collective oscil-
lation of electrons in ‘plasmonic’ structures for
lightcapture.Theabilitytodetectandmaplight
elements,includinghydrogen,couldextendthe
existingcapabilityofanalyticalelectronmicro­
scopy to the study of organic materials such
as polymers and pharmaceuticals, as well as
energy-storagematerials—ifissuesassociated
with electron-beam-induced damage can be
addressed. Directly measuring phonons could
potentially help to identify chemical reactions
involving the surfaces of nanoscale hetero­
geneous catalyst particles, and could aid the
investigationofthetransmissionoflatticevibra-
tionsacrossmicro-andnanostructuralfeatures,
such as interfaces and defects in thermal and
opticalmaterials.Aswiththeemergenceofany
newtechnique,manyadditionalresearchareas
may ultimately prove to be most fruitful.
Existing theory suggests that electrons that
have undergone phonon scattering would be
scattered through large angles and the result-
ing phonon signal would be spatially highly
de­localized, preventing atomic-resolution
analysis. However, Krivanek and colleagues
present some initial findings which, together
with recent theoretical predictions8
, suggest
that under appropriate conditions the phonon
signalmaybesufficientlylocalizedforthestudy
of vibrations at a spatial resolution better than
that achieved by scanning probe tip-enhanced
vibrational spectroscopies9
. The authors
observed an exponential delocalization of the
phonon signal as an electron probe is moved
away from the surface of a sample and into the
surroundingvacuum.However,thereseemsto
beamorelocalizedcomponentofthesignalthat
peaksinintensityclosetothesurfaceitself,and
the researchers discuss a possible experimen-
tal geometry for signal collection that would
ANIMAL BEHAVIOUR
Incipient tradition in
wild chimpanzees
The adoption of a new form of tool use has been observed to spread along
social-network pathways in a chimpanzee community. The finding offers
the first direct evidence of cultural diffusion in these animals in the wild.
enhance this more localized contribution.
Furthermore,iftheprobeisinsidethesample,it
seemsthatthedelocalizationcouldbescreened
at the interface between two mater­ials with
different electrical properties.
The authors also demonstrate a method for
remotely exciting such phonons at a surface
using the inherent delocalization of the signal;
here, the beam is located in the vacuum close
to the edge of a sample, potentially helping to
mitigate electron-beam-induced damage of
radiation-sensitive samples. These investiga-
tions of the spatial resolution of the phonon
signal represent a clear example of experiment
leading theory in terms of the interpretation of
the results, and is indicative of the new experi-
mental landscape that this development in
instrumentation unfolds. Undoubtedly, many
more exciting experiments with this technol-
ogy will follow, aided by the delivery, later
in 2014, of a third-generation instrument to
a shared user facility: the Engineering and
Physical Sciences Research Council National
Facility for Aberration-Corrected STEM,
or SuperSTEM10
, in Daresbury, UK. I look
forward to the community charting this new
frontier of research. ■
Rik Brydson is at the Institute for Materials
Research, School of Chemical and Process
Engineering, University of Leeds,
Leeds LS2 9JT, UK.
e-mail: r.m.drummond-brydson@leeds.ac.uk
1. Krivanek, O. L. et al. Nature 514, 209–212 (2014).
2. Krivanek, O. L. et al. Phil. Trans. R. Soc. A 367,
3683–3697 (2009).
3. Krivanek, O. L. et al. Microscopy 62, 3–21 (2013).
4. Bleloch, A. & Ramasse, Q. in Aberration-Corrected
Analytical Transmission Electron Microscopy
(ed. Brydson, R.) Ch. 4, 55–87 (Wiley, 2011).
5. Egerton, R. F. Electron Energy Loss Spectroscopy in
the Electron Microscope 3rd edn (Springer, 2011).
6. Mahan, G. D. Condensed Matter in a Nutshell
(Princeton Univ. Press, 2010).
7. Williams, D. B. & Carter, C. B. Transmission Electron
Microscopy 2nd edn (Springer, 2009).
8. Dwyer, C. Phys. Rev. B 89, 054103 (2014).
9. Hermann, P. et al. Analyst 136, 1148–1152 (2011).
10. www.superstem.org
ANDREW WHITEN
S
ocial learning — learning from others —
is one of the fastest-expanding research
fields in animal behaviour1,2
. At the
fundamental level of evolutionary biology,
social learning provides a high-speed ‘second
inheritance system’ that interacts with genetic
inheritance to enrich behavioural evolution2
.
Fromamoreanthropocentricperspective,ani-
malsociallearningcastslightontheevolution-
ary foundations of the cultural capacities that
make our own species so successful. Studies
of putative cultural variations in wild chim-
panzees2–4
, the primates with which (together
with bonobos) humans last shared a common
ancestor, have been particularly influential
in our understanding of behavioural evolu-
tion. But these observed regional behavioural
differences have displayed little change, mak-
ing it difficult to investigate the workings of
social learning. Now, writing in PLoS Biology,
Hobaiter et al.5
describe a new form of tool use
intheSonsocommunityofchimpanzeesofthe
Budongo Forest in Uganda, and present a sta-
tistical technique for tracing the social trans-
mission of this innovation.
Chimpanzees at Sonso fold wads of leaves in
theirmouthstofashiona‘leafsponge’thatthey
dip into tree holes to extract water to drink. In
2011, the researchers observed the dominant
male of the group, Nick, creating a sponge of
moss gathered from a tree trunk and using it
to drink from a small flooded waterhole —
a behaviour not previously recorded in the
20-year research programme at the site. He
was watched by the dominant female, Nambi.
Over the next six days of intensive and often
competitive use of the waterhole (which the
researchers suspect contained unusual densi-
ties of minerals or other desirable content),
Nambi and six other chimpanzees began to
display the moss-sponging technique (Fig. 1a).
More than 20 other individuals drank at the
hole or in puddles around it, but either directly
with their mouths or using leaf sponges rather
than moss sponges.
Toestablishwhetherthisbehaviouralspread
was due to social learning, the researchers
developed a form of network-based diffusion
analysis (NBDA). This statistical technique
quantifies the extent to which the spread of a
newbehaviourisconsistentwiththeprediction
that it will follow the social network — a
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2. numerical representation of who associates
most closely with whom in the community.
An impressive recent example of NBDA6
used
more than 73,000 observations of 653 hump-
back whales during the 27-year spread of a
‘lobtail’ prey-capture technique, which dif-
fused as predicted by the social network,
implying social learning. However, NBDA
studies have so far used only a static, summary
quantification of the social network. Hobaiter
et al. took this approach to a new level, which
they describe as dynamic NBDA, by incor-
porating repeatedly updated information
on whom each individual was likely to have
watched (those within 1 metre of and facing
the current sponger). They found strong evi-
denceconsistentwithsocialtransmission,with
an estimated 15-fold enhancement of moss-
sponging behaviour for each time a novice
observed an existing moss-sponger.
Ofcourse,NBDAandotherpurelystatistical
approaches to analysing observational data are
essentially correlational and thus do not nec-
essarily imply cause. To interpret such data,
one has to try to rule out alternative potential
explanations — in this case, for example, that
the order of acquisition observed in the chim-
panzees resulted not from social learning but
from rank-based queuing to gain access to the
waterhole, with each lower-ranked individ-
ual happening to watch the previous higher
ranker before they got their turn. It seems
that this possibility can be excluded, because
the ‘lower rankers’ were often offspring of the
higher-ranked earlier moss-spongers and so
had simultaneous access to the waterhole, yet
started to use moss only after watching their
mothers. However, caution is still warranted in
interpreting these findings in case some subtle
alternative factor explains the observed puta-
tive evidence for social learning.
Experimental approaches can provide
more-robust tests of causality. Indisputable
cases of social learning have already been seen
in captive primates, including chimpanzees,
in studies in which alternative techniques for
usingtoolsorotherwisemanipulatingforaging
tasks are seeded and subsequently spread in
different groups7
. Such approaches are inher-
ently difficult to engineer in the field, but a
few attempts have been made (see ref. 8 for a
review). Unfortunately, this method has yet to
be successfully implemented with wild chimp­
anzees, which are surprisingly neophobic.
Nevertheless, non-interventional studies of
natural behaviour, such as the one presented
by Hobaiter et al., are vital to the field. Experi-
mental studies make good sense only when
they build on what has first been established
in the wild. The innovation recorded by the
authors was not dramatic — it was merely a
modification of existing leaf-sponging exper-
tise. But the findings are valuable as the first
direct evidence of cultural diffusion in this key
species, converging with observational evi-
dence from the wild and rigorously controlled
experiments in captive animals to consolidate
a substantial case for the role of cultural trans-
mission in such cases.
This study follows hot on the heels of
another9
documenting the diffusion of a par-
ticularly intriguing innovation — placing a
blade of grass in the ear — in chimpanzees liv-
ing in four large enclosures in an African sanc-
tuary (Fig. 1b). That study is unusual because
the behaviour seems to be functionless, and
thus akin to human cultural phenomena such
as fads and fashions. The grass-in-ear behav-
iour spread from one apparent inventor in
2007 to seven others by 2012, in just one of the
four groups. The lack of overt function makes
any explanation other than social learning dif-
ficult to accept, and underlines the potential
potency of this form of learning in this species.
Researchers have also claimed the first
documented case of successful transmission
of a novel cultural behaviour — fishing for
wood-boring ants using peeled bark or
other material — between wild chimpanzee
communities10
. And in other studies of
the selection of materials for nut-cracking,
researchers concluded that migrating female
chimpanzees soon conform to the practices
of the group they move into11
. A major ques-
tion for the future is thus what determines the
outcome of such migrations between different
local cultures. Why do migrants sometimes
seed behaviours that diffuse in their new com-
munity in the manner demonstrated in the
moss-sponging study, whereas others instead
abandon previous behaviours and conform
to the new local norms? Investigating which
factors throw this important switch will add
considerably to our understanding of cultural
transmission in animals. ■
Andrew Whiten is at the Centre for Social
Learning and Cognitive Evolution, School of
Psychology and Neuroscience, University of
St Andrews, St Andrews KY16 9JP, UK.
e-mail: a.whiten@st-andrews.ac.uk
1. Hoppitt, W. & Laland, K. N. Social Learning: An
Introduction to Mechanisms, Methods, and Models
(Princeton Univ. Press, 2013).
2. Whiten, A. Nature 437, 52–55 (2005).
3. Nishida, T., Zamma, K., Matsusaka, T., Inaba, A. &
McGrew, W. C. Chimpanzee Behavior in the Wild:
An Audio-Visual Encylopedia (Springer, 2010).
4. Boesch, C. Wild Cultures: A Comparison between
Chimpanzee and Human Cultures (Cambridge Univ.
Press, 2012).
5. Hobaiter, C., Poisot, T., Zuberbühler, K., Hoppitt, W.
& Gruber, T. PLoS Biol. 12, e1001960 (2014).
6. Allen, J., Weinrich, M., Hoppitt, W. & Rendell, L.
Science 340, 485–488 (2013).
7. Whiten, A. & Mesoudi, A. Phil. Trans. R. Soc. B 363,
3477–3488 (2008).
8. van de Waal, E., Borgeaud, C. & Whiten, A. Science
340, 483–485 (2013).
9. van Leeuwen, E. J. C., Cronin, K. A. & Haun, D. B. M.
Anim. Cogn. http://dx.doi.org/10.1007/s10071-
014-0766-8 (2014).
10. O’Malley, R. C., Wallauer, W., Murray, C. M. &
Goodall, J. Curr. Anthropol. 53, 650–663 (2012).
11. Luncz, L. V. & Boesch, C. Am. J. Primatol. 76,
649–657 (2014).
Thisarticlewaspublishedonlineon1October2014.
a b
Figure1|Toolsandtrends. a, AchimpanzeefromtheSonsocommunityusingamossspongetodrinkfromawaterhole.Hobaiteretal.5
observedthatthisnewtool
usespreadfromoneanimaltoothersalongthecommunity’ssocialnetwork.b, Anotherstudy9
reportsthespreadofanewandseeminglyuselessbehavioural‘fad’ —
stickingabladeofgrassintheear—amongchimpanzeesinacaptivesanctuarycommunity.
A:CATHERINEHOBAITER/B:EDWINVANLEEUWEN
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