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Fri, 19 Aug 2011 22:34:37 -0400
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Apes in Africa: The Cultured Chimpanzees

     Do chimpanzees have traditions? As wild populations
     dwindle, researchers are racing to find out.

Gayathri Vaidyanathan
Published online 17 August 2011 |
Nature 476, 266-269 (2011) | doi:10.1038/476266a

Thump! Thump! Thump! As the hollow sound echoes through
the Liberian rainforest, Vera Leinert and her fellow
researchers freeze. Silently, Leinert directs the guide
to investigate. Jefferson 'Bola' Skinnah, a ranger with
the Liberian Forestry Development Authority, stalks
ahead, using the thumping to mask the sound of his

In a sunlit opening in the forest, Skinnah spots a large
adult chimpanzee hammering something with a big stone.
The chimpanzee puts a broken nut into its mouth then
continues pounding. When Skinnah tries to move closer,
the chimp disappears into the trees. By the time Leinert
and her crew get to the clearing, the animal is long

For the past year, Leinert has been trekking through
Sapo National Park, Liberia's first and only protected
reserve, to study its chimpanzee population. A student
volunteer at the Max Planck Institute for Evolutionary
Anthropology (EVA) in Leipzig, Germany, Leinert has
never seen her elusive subjects in the flesh but she
knows some of them well. There's an energetic young male
with a big belly who hammers nuts so vigorously he has
to grab a sapling for support. There are the stronger
adults who can split a nut with three blows. And there
are the mothers who parade through the site with their
babies. They've all been caught by video cameras placed
strategically throughout Sapo.

Chimpanzees in the wild are notoriously difficult to
study because they flee from humans - with good reason.
Bushmeat hunting and human respiratory diseases have
decimated chimpanzee populations1, while logging and
mining have wiped out their habitat. Population numbers
have plunged - although no one knows by exactly how much
because in most countries with great apes, the animals
have never been properly surveyed.

The Pan Africa Great Ape Program, the first Africa-wide
great-ape census to be mounted, could change that. In
addition to surveying chimpanzee numbers (see 'How many
chimpanzees are left?'), project scientists plan to set
up automated video and audio recording devices at 40
research sites in 15 countries with chimp populations.
Led by Christophe Boesch, director of the primatology
department at the EVA, and Hjalmar Kühl, also at the
EVA, the programme aims to get a picture of how
chimpanzee behaviour - from nut cracking to vocal calls
- varies across Africa. Ultimately, the hope is to learn
about the origins and extent of what, in humans, would
be called culture.

Until recently, scientists regarded culture - defined as
socially transmitted behaviours - as exclusive to
humans, but there is growing recognition that many
animals exhibit some sort of culture. Chimpanzees, which
share 98% of their genes with humans, have the most
varied set of behaviours documented in the animal world.
The difference between humans and animals is growing
less distinct, say some researchers. "It is not black
and white," says Kühl, who is Leinert's supervisor at
the EVA.

In the old scenario, "only humans have culture", says
Jason Kamilar, a biogeographer in the department of
anthropology at Yale University in New Haven,
Connecticut. "Then, culture would be the defining
feature of humanity, which evolved some time after the
split between the human and chimp lineages," he says.
But "if chimps have culture, then presumably the last
common ancestor of chimps and humans had culture".

Mapping behaviour

Some chimps dance slowly at the beginning of rain
showers, others don't; some use long sticks to dig up
army ants; others use short sticks. In West Africa, some
chimp groups hammer nuts with a stone or a piece of wood
to open them. But east of the river Nzo-Sassandra, which
cuts across Côte d'Ivoire, only one group has been seen
cracking nuts.

So far, researchers have observed these variations over
years spent studying groups of chimpanzee that have been
carefully habituated to the presence of humans. There
are just 12 such colonies in Africa (see 'Chimpanzee
census'), the most famous of which is in Gombe Stream
National Park in Tanzania, where primatologist Jane
Goodall worked.

In 1999, evolutionary psychologist Andrew Whiten of the
University of St Andrews, UK, and his colleagues
compiled a list of behaviours seen in seven of those
groups and showed that chimpanzees have unique
traditions depending on where they live2. They
identified at least 39 behaviours from a list of 65 that
varied between groups for no obvious reason.

In humans, culture is passed on from one person to
another, and in laboratory studies chimpanzees have
shown the capacity to pass on learned customs. In one
experiment, Whiten and his colleagues taught two chimps
a complex series of steps for getting food from a box.
Soon after the chimps were reunited with their groups,
all the animals were using this method to get their
food3. But whether such social learning happens in the
wild is less clear. Gorillas and bonobos can also learn
to use tools in the lab, but rarely use them in their
natural habitat4.

Deciphering culture in the wild is difficult because
researchers must ensure that behavioural differences
between groups do not have other causes, such as
variation in genetics or environmental conditions. "Why
is it all chimps don't do everything? One solution is
that there are hidden ecological differences between
populations," says primatologist Richard Wrangham at
Harvard University in Cambridge, Massachusetts. A
behaviour could be linked to any number of variables
such as amount of rainfall, the types of tree available,
or the kinds of predator in the area, he says.

"The difference between humans and animals is growing
less distinct."
These influences can be subtle, as researchers found
while studying how chimps use sticks to harvest army
ants. Chimpanzees in Guinea sometimes use short sticks
and sometimes use sticks up to twice as long. No reason
for this was obvious until Tatyana Humle, an
anthropologist at the University of Kent, UK, found that
some ants are more aggressive, with longer legs and
larger mandibles; they run up sticks quicker and bite
harder5. This might explain why chimps elsewhere in
Africa also choose tools of varying lengths to get at

But researchers have not been able to find obvious
explanations for other variations related to ant
harvesting. Chimpanzees in Cote d'Ivoire sweep the ants
off their sticks and into their palms before eating; in
Guinea, only about 320 kilometres away, the animals
stick the ant-laden sticks directly into their mouths.
The same type of ant is present in both places.

Ruling out genetic influences is equally complicated.
This year, molecular ecologist Kevin Langergraber at the
EVA and his colleagues compared genetic and behavioural
data for nine groups of chimpanzee. They found that
communities with greater overlap in their mitochondrial
DNA showed more similarities in their behaviour6. "What
we are saying is, you haven't really ruled out the
genetic explanation," says Langergraber.

There may be a few hundred thousand chimpanzees in
Africa, but researchers have studied just 700-1,000
chimpanzees at the dozen sites with well habituated
colonies, says Whiten. The available information from
those groups is too little to determine how genes and
the environment influence behavioural variations. Kühl
compares the situation to using a handful of villages
scattered around the world to draw basic conclusions
about all the rituals that define human culture.

Whiten and his colleagues are now carrying out more
detailed comparisons of the behaviour and ecology of
chimps at all the habituated sites. But it has taken 50
years to capture the data they are using, most of which
were recorded by painstaking observational studies.

The way forward may be the use of cameras hidden in
strategic sites, like those Leinert and her team are
setting up in Liberia. Such techniques have already
proved their worth. Two years ago in Gabon, Boesch and
his team were puzzled by random pits they observed in
the ground. They set up camera traps and obtained video
recordings of chimps digging to extract honey from
underground bees' nests - something that had never been
seen before7. "Camera traps are proving to be an
exciting way to reveal new and often complex behavioural
techniques in wild chimpanzee communities," says Whiten.

Caught in the act

At the site in Sapo, Leinert pulls on gloves to measure
the rock used by the chimp to crack open nuts of the
Guinea plum, Parinari excelsa. The rock is sizeable,
weighing in at 880 grams. She collects nuts for later
analysis, as well as hair and dung samples for genetic

Leinert may later put up a video camera at the location
to collect more data on the nut-cracking behaviour. The
cameras are mounted in boxes on tree trunks at the
height of a chimp's shoulder, and powered by
rechargeable batteries. An infrared motion detector
activates the camera for one minute when anything moves
in its range.

Near the nut-cracking site, a solar-powered audio device
is already continuously recording the forest sounds.
Chimpanzees emit a range of calls, including short,
high-pitched 'pant hoots' that are unique to each
individual, and researchers can use them to identify
individuals and to tally the size of a community. These
calls may be a form of vocal culture, somewhat like
human dialects8.

Over the next five years, the Pan Africa Great Ape
Program will establish similar recording stations at
locations across Africa. "So potentially we might have,
in a few years, behavioural differences from 40
different populations, which is, as you know, four times
more than what we have now," says Boesch.

Kühl proposes that these data could help in designing
computer models to test how genes, ecology and social
transmission influence the distribution and spread of
behaviours such as nut cracking. One idea is that when
female chimpanzees reach sexual maturity and move to new
communities, they pass along their learned behaviours.
Another possibility is that each group invents its own
behaviours, some of which catch on and become a culture.
Individual practices can die out in particular groups
but thrive in others. Or, it might be that some chimp
groups refuse to take up new ways of doing things from
incoming individuals. This could explain why some
populations show similar behaviours and others do not.

Before Kühl and his colleagues can conduct the modelling
work, they need to devise a faster way to go through the
recordings made by the camera and audio traps, which are
accumulating at a rate of hundreds of hours each month.
Students are currently carrying out the analysis but it
can take 10 hours to go through an hour of video,
according to Kühl. So engineers at the Fraunhofer
Institute for Digital Media Technology, based in
Ilmenau, Germany, have developed a computer algorithm to
recognize individual chimpanzees from their facial
patterns and distinctive features, such as the wrinkles
under their eyes. In tests of zoo animals, the software
can correctly identify individual chimpanzees 83% of the
time, and it processes recordings ten times faster than
a person can.

Nevertheless, the cameras cannot reveal how an adult
chimp patrols its range, or other actions that play out
over a wide area. The full portfolio of traditions in
the community will remain a mystery. And automated
recordings will never capture the subtle ecological
information - such as the mandible size and leg length
of army ants - that may eventually explain particular
behaviours. These require boots on the ground, and long-
term behavioural studies are needed to see how
chimpanzees pass traditions on to each other as a driver
of culture.

But already, the 30 cameras that Leinert has set up in
Sapo Park have delivered some tantalizing clues. She is
most interested in the lively young male she calls
'Janosch', whom she likes for "his big belly and the way
he strikes out to crack the nuts". Besides being
entertaining, he sometimes carries his pounding rock
away with him, something Leinert hasn't seen with most
other chimpanzees in Sapo. The practice may yet catch on
with others there. If so, Leinert could be seeing the
beginnings of a cultural variation, captured by the
cameras she set up in the forest.

Gayathri Vaidyanathan is an International Development
Research Center fellow at Nature.


1 Köndgen, S. et al. Curr. Biol. 18, 260-264 (2008).

2 Whiten, A. et al. Nature 399, 682-685 (1999).

3 Whiten, A. , Horner, V. & de Waal, F. B. M. Nature
437, 737-740 (2005).

4 McGrew, W. C. Science 328, 579-580 (2010).

5 Schöning, C. , Humle, T. , Möbius, Y. & McGrew, W. C.
  J. Hum. Evol. 55, 48-59 (2008).

6 Langergraber, K. E. et al. Proc. R. Soc. B 278,
  408-416 (2011).

7 Boesch, C. , Head, J. & Robbins, M. M. J. Hum. Evol.
  56, 560-569 (2009).

8 Mitani, J. C. , Hasegawa, T. , Gros-Louis, J. ,
  Marler, P. & Byrne, R. Am. J. Primatol. 27, 233-243


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