Chimps trump university students at memory task

Blogging on Peer-Reviewed ResearchWe humans aren’t used to having our intelligence challenged. Among the animal kingdom, we hold no records for speed, strength or size but our vaunted mental abilities are unparalleled. That is, until now. New research from Kyoto University shows that some chimps have a photographic memory that puts humans to shame.

Chimps trump university students at memory taskSana Inoue and Tetsuro Matsuzawa have found that young chimps have an ability to memorise details of complex images that is literally super-human. Boffin chimp Ayumu, outperformed university students in memory tasks where they had to rapidly memorise numbers scattered on a touchscreen and press them in numerical order.

This is the first time that an animal has outmatched humans in a mental skill. Recently, I’ve previously blogged about animals that show abilities once considered to be uniquely human, including jays that can plan for the future, rats that know how much they know, cultured chimps, tool-combining crows, and discriminating elephants.

But in all these cases, the animals merely showed that they could do similar types of mental feats to us. They never challenging our abilities in terms of complexity or scale. Simply put, a crow may be able to combine tools together, but it’s never going to be able to engineer a computer.

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Altruistic chimpanzees clearly help each other out

Many scientists have argued that only humans show true altruistic behaviour. But a group of Ugandan chimps is set to change all that by showing clear signs of true selflessness, helping other unrelated chimps with no desire for reward.

Why do we help each other, instead of constantly looking out for ourselves? This is one of the most compelling questions in modern biology. Evolutionary and game theory alike predict that selfish behaviour should be the rule with altruism the exception, and animal experiments have largely supported this idea.

Nature, ‘red in tooth and claw’, is painted as a fierce competition between selfish individuals and their even more selfish genes. In this stark landscape, true altruism is a rare quality and some scientists believe that it’s one that only we humans possess.

Even our closest relatives, chimpanzees, are not exempt from this dividing line. Certainly, there is a large amount of anecdotal evidence of chimps helping each other or even saving each others’ lives. But some thinkers believe that this behaviour, along with other seemingly selfless animal acts, is actually self-serving in one of two ways.

The chimps could be helping their relatives in order to advanced the spread of its own genes, which family members are likely to share. Or they could be doing a favour for another individual, in the knowledge that it will be repaid later on. Either way, it’s the do-gooder that eventually benefits.

Humans, on the other hand, seem to flaunt this rule. We often help others who are not relatives and who are unlikely to repay the favour. We go out of our way to be helpful, and sometimes even risk personal harm to do so.

Two tests for altruism

Now, Felix Warneken and colleagues form the Max Planck Institute for Evolutionary Anthropology have found compelling evidence that we are not alone. Contrary to previous studies, they have found that chimps also behave altruistically in a very human way. They help out unrelated strangers without expectation of reward, and even go to great lengths to do so.

Warneken studied 36 chimps at Ngamba Island Chimpanzee Sanctuary, Uganda and looked at their willingness to help a human handler. To minimise the effect of any human-chimp bond, he only looked at chimps that were born in the wild, and used experimenters who the chimps had never seen before.

In the first test, the chimps saw a human unsuccessfully trying to reach a stick that they themselves could reach. Warneken found that chimps were all too happy to pass the stick across (video), regardless of whether they were rewarded with a banana or not. In fact, the only thing that affected their readiness to lend a hand was whether the human was struggling for the stick or just passively staring at it.

He found the same thing when he ran a similar set-up with a 36 eighteen-month-old human toddlers, but with toy cubes in lieu of sticks (video). At that age, a baby’s mental abilities are thought to similar to those of chimps, and indeed the only real difference between the two was that the babies were quicker with their assistance.

Passing a stick across is obviously fairly easy but would altruism persist if there was effort involved? Warneken tested this by changing the experiment so that the chimps had to climb over a raceway (video) and the toddlers had to walk past a series of obstacles (video). Those that helped in the first test were happy to do so in the second, again without any rewards.

The third and most important test

A skeptic might argue that this doesn’t show anything. During their stay at the sanctuary, the chimps could have learned that helping any one of their strange two-legged keepers was worth it. The acid test then, was to see if the chimps would help each other.

The first chimp – the subject – could only get into a room with food by lifting the chain attached to its door. But it couldn’t reach the chain – only a second chimp, the observer, could do that. And once again, the chimps proved their selflessness, lifting the chain for their fellow chimps the vast majority of the time (video).

This striking result flies in the face of other studies, which have failed to find altruistic behaviour between chimps. But in a related commentary, Frans de Waal, an international expert of ape behaviour, claimed that these were more tests of generosity than selfishness.

They created specific situations where chimps were motivated to look out for themselves and the species can’t be judged on these scenarios alone. It would be like claiming that all people are selfish after watching the self-interested behaviour of commuters. Failing to show altruism is not the same as proving that it doesn’t happen.

But it does happen – Warneken’s experiments are striking indicators of that. In the third test, the chimps were unrelated, the observer had no chance of getting a share of the food, and their roles were never reversed so there were no opportunities for payback. Clearly, humans are not alone in our desire to help each other. Chimps are now our fellows in altruism and it’s likely that our common ancestor did the same.

What this means for the altruism debate

It’s particularly fascinating that rewards in the first two tests didn’t affect the chimps’ behaviour. This suggests that chimps don’t continually analyse the pros and cons of helping their fellow – if they did, the reward would have motivated them to help even more often.

Instead, de Waal believes that the chimps have evolved psychological systems that steer them towards selflessness. In essence, natural selection has done the analysis for them and decided that altruistic behaviour works to its advantage in the long run. Selfless behaviour then, can evolve for selfish reasons, and that strikes to the very core of the debate on altruism.

Spend enough time reading about this field of research, and you could be forgiven for thinking that some scientists are taking cynical glee at ‘explaining away’ altruism. The extreme reductionist view is that discovering the evolutionary origins of selfless behaviour discredits that behaviour, somehow making it less worthy. As Robert Trivers put it, these models are designed to “take the altruism out of altruism”.

But this viewpoint is blinkered and too focused on the past. Evolutionary explanations can help us understand where an unusual behaviour like selflessness comes from, but they do not alter the value of those behaviours. They can tell us about how a behaviour arose, but not about an animal’s reasons for behaving in that way here and now.

Take sex. Its adaptive benefits are clear – it continues the line and promotes genetic diversity. But animals don’t consider the issue of reproduction every time they have sex and for the most part, humans actively deny it!

According to de Waal, we should now turn our attention to the psychological processes that foster altruism in chimps, and how they are different from those that work in our own minds. Do chimps share our strong sense of empathy, that fuels selflessness by letting us identify with the emotions and needs of others. Do their cultures, like ours, punish and vilify selfish behaviour?

References: Warneken, Hare, Melis, Hanus & Tomasello. 2007. Spontaneous altruism by chimpanzees and young children. PLOS Biology 5: e184.
de Waal. 2007. With a little help from a friend. PLOS Biology 5: e190.

Related posts on chimps:
Chimps show that actions spoke louder than words in language evolution
Not so unique – the chimpanzee Stone Age, and our place among intelligent animals
Cultured chimps pass on new traditions between groups
Chimpanzees make spears to hunt bushbabies

Related posts on altruism:
Army ants plug potholes with their own bodies

Images: from BBC, Nature, Jane Goodall Institute and Ngamba Sanctuary

Cultured chimps pass on new traditions between groups

Chimpanzee groups have their own cultural traditions. Now, scientists have shown that chimp groups can transmit new behaviours to each other, by seeding new behaviours into a group and watching them spread.

For humans, our culture is a massive part of our identity, from the way we dress, speak and cook, to the social norms that govern how we interact with our peers. Our culture stems from our ability to pick up new behaviours through imitation, and we are so innately good at this that we often take it for granted.

Chimpanzee groups can learn new traditions from each other.We now know that chimpanzees have a similar ability, and like us, different groups have their own distinct cultures and traditions.

Now, Andrew Whiten from the University of St Andrews has published the first evidence that groups of chimpanzees can pick up new traditions from each other. In an experimental game of Chinese whispers, he seeded new behaviours in one group and saw that they readily spread to others.

Chimp cultures

Many animals have their own cultural traditions. Songbirds, for example, copy their parents’ melodies, and small variations lead to groups with different dialects. But chimpanzees have by far the richest cultures so far observed.

These scope of their culture first came to light in 1999, when Whiten, together with Jane Goodall and others, carefully documented at least 39 cultural behaviours among wild chimpanzees. Many of these were a matter of course in some populations, but completely absent in others.

Some groups use sticks to extract honey, others use them to retrieve marrow from bones, and yet others use them to fish for ants. Some get attention by rapping their knuckles on a branch, while others noisily rip leaves between their teeth. Some groups even have a rain dance.

Whiten has previously published three studies which demonstrated different sides of chimp cultural transmission. The first showed that trained individuals can spread seeded behaviours within a group. The second showed that cultures trickle through the generations as parents teach their children new behaviours. And the third showed that arbitrary conventions such as gestures and displays can spread as easily as skills involving tool use.

Now, together with an international team of researchers from the University of Texas and Yerkes National Primate Research Center, including primate expert Frans de Waal, Whiten has produced the first experimental evidence that cultural transmission can happen between different groups.

Seeding behaviours in groups

Whiten worked with six groups of captive chimps, each consisting of 8-11 individuals. They lived in large but separate enclosures arranged in two rows of three and each group could observe its neighbours, but not interact with them.

Whiten trained one chimp from groups one and four to solve two difficult tasks – the ‘probe task’ and the ‘turn-ip’ task – in order to get some food hidden inside a box. Each chimp was taught to use a different technique.

The probe taskIn the probe task, the chimp could move a lever at the top of the box to open a hatch, and use a stick to impale the food (A). Alternatively, it could use another lever at the side to lift an opening, giving it enough room to manoeuvre a stick inside and push the food out (B).

The turn-ip taskIn the turn-ip task (C), food items were dropped down a pipe, where they were blocked by a disc. The disc had a hole in it, that would allow the food to fall through when it was properly aligned. The chimps could turn the disc either by rotating an exposed edge or using a ratchet. Once the food dropped through, the chimps could get at it by pressing or sliding one of two different handles.

Group transmission

Once the student chimps had mastered their new methods, they were returned to their respective compounds and the whole group was allowed to try its hand at the tasks. Before the training, none of the chimps managed to successfully get at the food. But after just one chimp was taught the technique, most of the others in the group quickly picked it up.

The boxes were then moved to a different position, where chimps from the second pair of groups could watch chimps from the first pair solving the task. After a time, it was moved to another position where the third pair of groups could watch the second one.

Whiten found that the techniques were accurately and quickly transmitted between the different chimpanzee groups. His experiment clearly shows that chimps have an immense capacity for learning new behaviours from their peers. They do this accurately and different groups can acquire and maintain several varied cultural traditions.

Different chimpanzee groups have distinct cultural traditions.In light of this evidence, the regional behaviour patterns seen in chimp groups across Africa are, without a doubt, the result of cultural transmission. In the wild, rival groups are often hostile towards each other and it is unlikely that chimps sit down in jungle conferences to share new ideas. But females do move between groups and Whiten believes that they carry new cultural traditions with them.

How exactly the new behaviours spread is still a matter for debate. Some scientists have suggested that the chimps learn by ‘emulation’, meaning that they focus on the results of actions rather than the actions themselves. But other studies found that chimps don’t respond to ‘ghost’ lessons, where task machinery is operated by remote and not by another chimp.

The most likely explanation is that chimps imitate the actions of other chimps and are very good at learning from each other. In all likelihood, the common ancestor that we share with chimps had the same ability, and also had strong cultural streams running through its populations.


Find out more: If you’re interested in chimp intelligence and evolution, have a look at some of my previous posts on chimp gestures and the evolution of language, the chimp Stone Age and the evolution of tool use, and their use of tools for hunting.

Reference: Whiten, Spiteri, Horner, Bonnie, Lambeth, Schapiro & de Waal. 2007. Transmission of multiple traditions within and between chimpanzee groups. Current Biology 17: 1-6.

Images: Image of experimental apparatus taken from Cell Press.

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Orang-utan study suggests that upright walking may have started in the trees

A common theory of human evolution says that after our ancestors descended from the trees, they went form walking on four legs to two. But a new study in orang-utans could overturn that theory, by suggesting that our ancestors evolved a bipedal walk while they were still in the trees.

Did and upright posture evolve in a tree-dwelling ancestor?Walking on two legs, or bipedalism, immediately sets us apart form other apes. It frees our arms for using tools and weapons and is a key part of our evolutionary success. Scientists have put forward a few theories to explain how our upright gait evolved, but the ‘savannah theory’ is by far the most prolific.

It’s nicely illustrated by this misleading image that has become a mainstay of popular culture. It suggests that our ancestors went from four legs to two via the four-legged knuckle-walking gait of gorillas and chimps. Dwindling forests eventually pushed them from knuckle-walking to a full upright posture. This stance is more efficient over long distances and allowed our ancestors to travel across open savannahs.

But this theory fails in the light of new fossils which push back the first appearance of bipedalism to a time before the forests thinned, and even before our ancestors split from those of chimpanzees. Very early hominins, including Lucy (Australopithecus afarensis) and Millennium Man (Orrorin) certainly ambled along on two legs, but they did so through woodland not plains.

Our arms provide a further clue. Even though our ancestors’ back legs quickly picked up adaptations for bipedalism, they steadfastly kept long, grasping arms, an adaptation more suited to moving through branches. To Susannah Thorpe at the University of Birmingham, these are signs that bipedalism evolved while our ancestors were still living in trees.

Two legs good, four legs bad?

Orang-utans can go bipedal and our ancestors may well have done the same in the trees.But there is a snag – an adaptation must provide some sort of benefit. And, as many children painfully discover, it is hard to imagine how walking on two legs could benefit sometime in a tree.

But Thorpe has an answer to this too. She spent a year in the Sumatran jungle, studying the orang-utan – the only great ape to spend the majority of its life in the trees.

She carefully documented over 3,000 sightings of wild orang-utans moving through the treetops. On large sturdy branches, they walk on all fours (below right), and on medium-sized ones, they start to use their arms to support their weight.

But on the thinnest and most unstable branches, the apes use a posture that Thorpe calls ‘assisted bipedalism’ (below left). They grip multiple branches with their long, prehensile toes and use their arms to balance and transfer their weight. And unlike chimps which bend their knees while standing up, bipedal orang-utans keep their legs straight, just like humans do.

An orang-utan used both two-legged and four-legged postures.

It’s a win-win posture – the hands provide extra safety, while the two-legged stance frees at least one hand to grab food or extra support. With it, the apes can venture onto the furthest and thinnest branches, which provides them with several advantages.

As Thorpe says, “Bipedalism is used to navigate the smallest branches where the tastiest fruits are, and also to reach further to help cross gaps between trees.” That saves them energy because they don’t have to circle around any gaps, and it saves their lives because they don’t have to descend to the ground. “The Sumatran tiger is down there licking its lips”, she said.

A new view of ape & human evolution

With these strong adaptive benefits, it becomes reasonable to suggest that bipedalism evolved among the branches. Based on this theory, Thorpe, along with Roger Holder and Robin Crompton from the University of Liverpool, have painted an intriguing new picture of ape evolution.

It begins in the same way as many others – with the rainforests of the Miocene epoch (24 to 5 million years ago) becoming increasingly patchy. For tree-dwelling apes, the gaps in the canopy started becoming too big to cross. But in Thorpe’s view, these ancestral apes were already using a bipedal stance, and different groups took it in separate directions.

Our ancestors were bipedal long before they came down from the trees.The ancestors of orang-utans remained in the increasingly fragmented canopy and became specialised and restricted there. The ancestors of chimps and those of gorillas specialised in climbing up and down trees to make use of food both in the canopy and on the ground. The postures used in vertical climbing are actually very similar to those used in four-legged knuckle-walking and this became their walk of choice on the ground.

The ancestors of humans abandoned the trees altogether. They used the bipedal stance that served them well on thin branches to exploit the potential of the stable land environment. Over time, they brought in further adaptations for efficient walking, culminating in the human walking style that we now neglect by sitting at a computer all day.

Thorpe’s reconstruction is delightfully non-human-centric. It suggests that in the evolution of movement, we were conservatives who relied on a walk that had been around for millions of years. Chimps and gorillas with their fancy new knuckle-dragging gait were the true innovators.

Reference: Thorpe, Holder & Crompton. 2007. Origin of human bipedalism as an adaptation for locomotion on flexible branches. Science 316: 1328-1331.

Image: Black and white image from Science magazine.

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Related stuff:
On ape and human evolution:
Chimps show that actions spoke louder than words in language evolution
Hidden ‘junk’ gene separates human brains from chimpanzees
Chimps have more adaptive genetic changes than humans

On the evolution of movement:
Salamander robot walks, swims and sheds light on evolutionary step from sea to land
Microraptor – the dinosaur that flew like a biplane

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Chimps show that actions spoke louder than words in language evolution

Chimpanzees and bonobos use gestures more flexibly and adaptively than other forms of communication. These gestures, and not words, may have been the starting point for the evolution of human language.

Hollywood cavemen typically communicate with grunts and snorts, reflecting a belief that human language originated like this and slowly evolved into the rich and sophisticated tongues we use today.

Chimps and bonobos have thier own vocabularies of gestures.But researchers from Emory University, Atlanta have found evidence that the origins of human language lie in gestures, not words. If they are right, then high-fives, V-signs and thumbs-ups could more closely reflect the beginnings of human language than conversations do.

The importance of gestures

All primates can communicate with each other through facial expressions, body postures and calls, but humans and apes are unique in their use of gestures. These go beyond simple postures or walking patterns – they are movements of the hand, limbs and feet, specifically directed at another individual.

We think of language as mainly spoken or written but gestures play an enormous, often overlooked role. After all, isn’t a speaker who waves their hands animatedly more engaging than one who stands motionless behind a podium?

And they are such an intrinsic part of the way we communicate that a blind speaker will make gestures normally to a blind audience, and babies use gestures long before they learn their first words.

To understand the role of gestures in the origins of human language, Amy PIllock and Frans de Wall decided to see how they are used by our closest relatives – the chimpanzee and the bonobo (the pygmy chimpanzee

How chimps and bonobos communicate

Bonobos may communicate with more sophistication than chimps.For one and a half years, they watched 34 chimps belonging to two separate groups, and 13 bonobos (right), again from two groups. Through painstaking analyses, they identified 31 different gestures and 18 different facial and vocal expressions.

The facial and vocal signals were very consistent between the two species. They were used in the same ways, and in very specific contexts, such as play, grooming or fights. For example, both chimps and bonobos scream when threatened or attacked, a gesture that is shared by many other primates.

This suggests that these signals are an evolutionarily ancient means of communication, and were probably used by the common ancestor that we shared with both chimps and bonobos.

Gestures on the other hand, were altogether more flexible. They were used in all sorts of situations and carried very different meanings depending on the context.

When a chimp stretches out an open hand (below), it can be asking for support during a fight or for a share of food during a meal. In the same way, a person raising his hand could be greeting a friend, surrendering, or answering a question in class.

Chimps use gestures more flexibly than other forms of communication.Chimps and bonobos also differed considerably in their vocabulary of gestures, with each species having its own ‘gesture culture’. The two groups of bonobos even used slightly different sets of gestures to each other.

Gestures and the origins of human language

Pillock and de Waal believe that these studies strongly position gestures as the starting point for human language evolution. In chimps and bonobos, gestures are more adaptable and flexible than calls or facial expressions.

They are relatively disconnected from specific emotions and can be more easily controlled. Facial expressions can give away big clues about a person’s emotional state in all but the best poker faces, but gestures can be used subtly or even deceptively.

Their adaptability means that gestures can be used in many ways and are free to pick up a variety of symbolic meanings. They pick up cultural differences easily, as shown by the very different ‘gesture vocabularies’ used by chimps and bonobos.

Pillock’s and de Waal’s experiments also support other studies which suggest that the language of bonobos is more sophisticated than that of chimps. For a start, their gestures show greater cultural variations.

While bonobos combine them with calls and facial expressions less frequently than chimps do, but they also respond much more strongly to these joint signals. Pillock and de Waal believe that the bonobos could be using these multiple signals more deliberately than chimps to subtly change the meaning of a facial expression or vice versa.

The chimps on the other hand, may just be using joint signals to say the same message more loudly. Among the great apes, the bonobos may deserve the silver medal for their language skills.

Reference: Pollick & de Waal. 2007. Ape gestures and language evolution. PNAS 104: 8184-8189

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Chimps have more adaptive genetic changes than humans

According to new research, chimpanzee genes have shown more adaptive changes than those of humans. The media widely reported the results as evidence that chimps are ‘more evolved’ than humans. But as I discuss here, these headlines are putting words into the researchers’ mouths.

Chimps have more adaptive genetic changes than humansSince the time when humans and chimps evolved from our common ancestor, our species appears to have come on by leaps and bounds. We walk on two legs, we speak using languages and while there is no doubt that chimps are intelligent, there is even less doubt that our brainpower outclasses theirs.

For years, scientists have assumed that our advanced abilities must be reflected in our genetics. After all, traits like intelligence and language give us great adaptive advantages. They should therefore be mirrored by similarly large changes in the human genome, compared to the chimp one.

Not so. Researchers at the University of Michigan sifted through the human and chimp genomes for signs of positive selection – the process where natural selection firmly embeds new mutations because of the advantages they provide. They found that the chimp genome contains 50% more positively-selected genes than the human one.

While earlier studies have compared individual human and chimp genes, this is the first to do a proper census. Margaret Bakewell and colleagues looked at almost 14,000 genes in both species.

The project was given a valuable push by the recent publication of the fully-sequenced rhesus macaque genome. The macaque – a type of monkey – is an evolutionary cousin of both humans and chimps, and provides a useful comparison.

Humans may have fewer adaptive changes than chimps because our population sizes have traditionally been smaller.If the team found a difference in the human and chimp genes, the macaque version can tell them which version is closest to the ancestral one. Previously, scientists had to make do with the mouse, a much more distantly related animal. The macaque’s presence gives the analysis greater accuracy.

Bakewell failed to find any noticeable differences in the function of positively-selected genes in humans and chimps. Both species even had similar proportions of positive changes among the genes that control the brain and nervous systems.

The reasons for this surprising result are unclear, but Bakewell feels that population sizes may hold the answer. For most of their evolution, chimpanzees have enjoyed a larger population size than humans have. It’s only recently that our numbers have ballooned to unfeasible proportions.

According to evolutionary theory, beneficial genetic changes are more quickly established in a population if it is larger. But in smaller groups, random genetic changes can trickle down through generations without being properly weeded out. This ‘genetic drift’ could explain why humans have fewer positively-selected genes than chimps do.

An alternative theory is that many of the human genetic changes that provide us with the greatest advantages may be relatively new developments. It is only recently in our history that we spread around the world from our origins in Africa, and as such, new genetic innovations may not have become established in the population as a whole.

A third theory, which I’m putting forward myself, is that the genetic changes responsible for our most human traits, may lie among stretches of DNA missed by this study. Recently, a study showed that one of the most important ‘genes’ in human evolution lies within our so-called junk DNA and controls the development of our brains. Clearly, we still have much to learn.

Evolution is not about progress.Nonetheless, the study helpfully shows that evolution is not necessarily about progress. It’s not an inexorable march toward some gleaming future. It’s about change, regardless of direction or result.

Somewhere along the line, the word ‘evolved’ started to gain a false value. It became an indicator of positive progress, so that claiming to be ‘more evolved’ than a peer is to claim superiority.

A huge number of newspapers and magazines reported this story under the headline of ‘Chimps more evolved than humans’. And while that may be technically reasonable, the inferences made were anything but.

The inherent values placed upon the phrase ‘more evolved’ clearly emerged in the reaction to the story. Some suggested that humans were obviously ‘less evolved’ given for reasons ranging from pollution to capitalism. Meanwhile, creationists and ID-supporters smelled blood in the water, and claimed that such as blatantly preposterous conclusion proved that evolution was nonsense.

Of course, no such conclusions were actually made by the study itself. In the light of the proper progress-free meaning of the word ‘evolution’, hese results are not preposterous, but fascinating. We should use them to drive a nail in the coffin of phrases like ‘evolutionary race’ or ‘more evolved’, at least in its value-laden non-scientific sense.

Reference: Bakewell, Shi & Zhang. 2007. More genes underwent positive selection in chimpanzee evolution than in human evolution. PNAS 104: 7489-7494.

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Opinion: Not so unique – the chimpanzee Stone Age, and our place among intelligent animals

This is the 50th article for this blog. I’ve been writing for it for over six months now, and I pleasantly surprised that I’m still finding the enthusiasm to write for it regularly, and that people seem to be reading it.

This special article considers new evidence for the origins of chimpanzee tool use. It is the third piece of research I’ve seen in the last few months which shows that other animals share an ability previously thought to be the sole province of humans. In this article, I consider why these discoveries are now coming to light, and what they mean for us.

In the Ivory Coast, a small stream called Audrenisrou winds its way through the lowland rainforest of the Tai National Park. On the floodplain of this stream, at a site called Nuolo, lie several stones that seem unassuming at first glance. But to the trained eye, they are a window to the past.

Chimps are advanced tool users, and have been for some timeTheir shape is different to other stones that have been worn away by natural erosion. They have been flaked in systematic ways and many are flattened and sharp. Clearly, they were shaped by hand for a purpose – they are tools.

Their creators were not humans, but close relatives who lived in these rainforests thousands of years ago – the ancestors of modern chimpanzees.

Nuolo: humans or chimps?

The Nuolo stones were uncovered by Julio Mercader form the University of Calgary, Christophe Boesch from the Max Planck Institute of Evolutionary Anthropology, and their colleagues. They are a magnificent archaeological find – the first ever evidence of prehistoric ape behaviour anywhere in the world.

Humans have a rich prehistoric past, informed by key archaeological finds like the Olduwan sites. These findings provide us with a window into the past, showing us how our ancestors developed the tools that continue to serve us well today. For chimps, no such sites have been found, until now.

Julio Mercador at the Nuolo excavationThe evidence that the Nuolo specimens were created by chimps is compelling. The density of stone pieces in the site, the preferred types of rocks, the length of the stone flakes and the patterns of wear closely mirror those of modern chimp tools.

They also carry the evidence of their past uses, as hammers and anvils for cracking nuts. Their crevices contain granules of starch that clearly came from nuts. Mercador and Boesch even managed to narrow the granules’ origins down to three possible species, all of which are currently cracked and eaten by today’s chimps. In contrast, the team found scant remains of tubers and legumes, the main food source of forest-dwelling humans.

This suggests that prehistoric humans who also, over time, visited the river-side site were not the creators of the Nuolo tools. But Mercador and Boesch found even stronger evidence.

Human hammers usually weight less than 400g, and even our ancestors’ anvils weighed no more than a kilogram. The far more powerful chimp with its larger hand can wield a tool many times heavier, anywhere from one to nine kilograms in weight.

Mercador and Boesch found that the stone tools at Nuolo most likely weighed about 2 kilograms, far too heavy heavier for a human but well within the limits of even a weak chimpanzee.

A chimpanzee Stone Age

A chimp cracks a nut with a stone hammerTogether, this evidence paints a remarkable picture of a chimpanzee Stone Age, when ancient chimps were clearly cracking nuts in the same way they do now, over four millennia ago.

Chimpanzees are highly advanced tool users. But some critics have sold short their abilities, claiming that they learned the use of tools by, for lack of a better word, apeing nearby humans.

The Nuolo finds puts paid to that suggestion. The tools predated the advent of farming in the rainforest by some time. Nuolo also lacks evidence of any of the other tools used by humans to grind and pound starchy tubers.

Among chimpanzees, nut-cracking is clearly a cultural tradition, passed down over time through over 200 generations of chimps. Humans and chimps either developed this technology independently, or they inherited it from a common ancestor who had already begun to use tools.

We’re not so unique after all

With studies like this, the list of attributes that are unique to humans seems to be getting smaller all the time. In just the last few months, scientists have found that chimpanzees hunt with spears, jays (below) can plan for the future, and even the long-dead dinosaur Bambiraptor, gripped prey with opposable fingers.

The beautiful western scrub-jay - a bird that can plan for the future.But as we start to come down from our pedestal, we should not mourn the loss of our position, but rejoice in our connectedness with the rest of the living world. These discoveries emphasise our position at the end of a continuous evolutionary spectrum, rather than atop a looming precipice.

The outdated view that we have been awarded special dominion over other life should be replaced by a humbler view, where our position of biological authority is tempered with respect.

Why has it taken so long for such findings to come to light? Centuries ago, anthropomorphism was commonplace and these experiments would have seemed like pointing out the obvious. But of late, biology has taken a more reductionist turn and signs of potential animal behaviour are scrutinised under the harshest and most sceptical light.

In many cases, this quite rightly avoids the false conclusions based on flimsy and anecdotal evidence. But while scientists have taken great care to ensure that their interpretations are not biased towards human perspectives, the same cannot always be said the design of the experiments themselves.

Looking for intelligence

One of the most significant problems with studying animal intelligence is that many species experience and react to the world in completely different ways to us. For example, to pass the classic test for self-awareness, an animal must show that it recognises itself in a mirror, by examining a mark previously made on its face (see right).

elephants-paper32.jpgGorillas and dogs tend to fail the mirror test, but not because they are mentally less advanced than successful examinees like elephants or chimps. Gorillas view direct eye contact is a sign of aggression and tend to avoid it, while dogs rely on smell as their primary sense, rather than sight.

Simply put, can we truly claim to understand the limits of another animal’s intelligence when we know so comparatively little about their behaviour or perceptions? Cleverly designed experiments may bring us closer to an answer, but sadly, we may never get the opportunity to conduct them.

800px-bottlenose_dolphin_ks.jpgSave ourselves, the most intelligent animals on the planet – the great apes, elephants, dolphins and whales – are mostly endangered, with many species facing a very real threat of extinction. Chimpanzees, like those in the Tai National Park are under threat from the loss of their habitat, and the illegal bushmeat trade.

A massive amount of evidence now paints these, our closest cousins, as sophisticated animals with their own culture. Imagine how tragic it would be if they died out for good, leaving only a set of shaped stones as the only lasting signs of their intelligence.

Reference: Mercader, Barton, Gillespie, Harris, Kuhn, Tyler & Boesch. 2007. 4,300-Year-old chimpanzee sites and the origins of percussive stone technology. PNAS 104: 3043-3048.

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