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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The social life of our extinct relatives

Blogging on Peer-Reviewed ResearchOne of our extinct evolutionary cousins, Paranthropus robustus, may have walked like a man but it socialised like a gorilla. Using only fossils, UCL scientists have found that P.robustus males were much larger than females, competed fiercely for mates and led risky lives under heavy threat from predators.

I wrote an article about the cool new finding for Nature Network. Here’s the opening and you can read the full article here.

A single fossil can tell you about the shape, diet and movements of an extinct animal but with enough specimens, you can reconstruct their social lives too.

Charles Lockwood of University College London used an unusually large collection of fossils to peer back in time at the social structures of one of our closest extinct relatives, Paranthropus robustus, which inhabited southern Africa between 1.2 million and 2 million years ago.

Envious capuchin monkeys react badly to raw deals

Blogging on Peer-Reviewed ResearchIn my last post, I wrote about two studies which showed that even bacteria cooperate towards a common goal and can be infiltrated by cheating slackers. In one of the studies, cheaters were eventually weeded out through natural selection because their rise to prominence created such havoc for the group that each individual bacterium suffered.

Envious capuchin monkeys react badly to raw dealsIn this scenario, slacking wasn’t punished but merely reduced over time. But more complex creatures, like humans, have the capacity to actually recognise unfairness and punish it directly. It turns out that we’re very keen on doing that; so strong is our innate sense of justice that we’ll often punish cheaters at our own expense.

Two years ago, Sarah Brosnan and Frans de Waal at the Yerkes National Primate Research Center found that brown capuchin monkeys also react badly to receiving raw deals. Forget bananas – capuchins love the taste of grapes and far prefer them over cucumber. If monkeys were rewarded for completing a task with cucumber while their peers were given succulent grapes, they were more likely to shun both task and reward.

That suggested that the ability to compare own efforts and rewards with those of our peers evolved much earlier in our history than we previously thought. Of course, animal behaviour researchers always need to be careful that they’re not reading too much into the actions of the animals they study.

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Resistance to an extinct virus makes us more vulnerable to HIV

Immunity to viral infections sounds like a good thing, but it can come at a price. Millions of years ago, we evolved resistance to a virus that plagued other primates. Today, that virus is extinct, but our resistance to it may be making us more vulnerable to the present threat of HIV.

Many extinct viruses are not completely gone. Some members of a group called retroviruses insinuated themselves into our DNA and became a part of our genetic code.

Our resistance to the ancient PtERV1 may explain our vulnerability to HIV.Indeed, a large proportion of the genomes of all primates consists of the embedded remnants of ancient viruses. Looking at these remnants is like genetic archaeology, and it can tell us about infections both past and present.

Viral hitchhikers

When retroviruses (such as HIV, right) infect a cell, they insert their own DNA into their host’s genome, using it as a base of operations. From there, the virus can pop out again and make new copies of itself, re-infect its host or move on to new cells.

If it manages to infect an egg or sperm cell, the virus could pass onto the next generation. Hidden inside the embryo’s DNA, it becomes replicated trillions of times over and ends up in every single one of the new individual’s cells.

These hitchhikers are called ‘endogenous retroviruses’. While they could pop out at any time, they quickly gain mutations in their DNA that knocks out their ability to infect. Unable to move on, they become as much a part of the host’s DNA as its own genes.

In 2005, a group of scientists led by Evan Eichler compared endogenous retroviruses in different primates and found startling differences. In particular, chimps and gorillas have over a hundred copies of the virus PtERV1 (or Pan troglodytes endogenous retrovirus in full). Our DNA has none at all, and this is one of the largest differences between our genome and that of chimps.

Our ancestors shared a similar geographical range to the ancestors of these apes, and would have encountered the same viruses, including PtERV1. And yet, we were spared from infection, while the apes were not. Why?

Protecting against an ancient virus

HIV daughter particles - retroviruses like HIV can integrate into a host’s DNAShari Kaiser and colleagues from the University of Washington and the Fred Hutchinson Cancer Research Center believed that the answer lies in a protein called TRIM5α that defends us from retroviruses. It latches onto the outer coat of incoming viruses, and tells other proteins to dismantle or destroy them.

Other primates have their own versions of TRIM5α that protect against a different range of viruses, and the protein has evolved dramatically in different primate lineages. Kaiser believed that our version of TRIM5α protected us from PtERV1, while that of other apes did not. To test her idea, all she had to do was to resurrect a dead virus.

Obviously, PtERV1 is long extinct, but its remnants exist inside the genomes of chimps. Kaiser compared dozens of these remnants and by identifying common elements, she worked out the ancestral sequence of the virus.

She created a small part of PtERV1 and fused it with bits of a modern virus, MLV, to create a fully-functioning hybrid. To nullify any potential for spread beyond the lab, she crippled the virus so that it could infect once and only once.

The reconstructed virus successfully infected mammal cells in a lab, but not when human TRIM5α was around. The guardian protein demolished the virus’s infectivity, reducing it by more than 100 times. As Kaiser predicted, our genomes are free of PtERV1 because TRIM5α killed it before it could reach our DNA.

Resist one virus, succumb to another

TRIM5a provides antiviral protection that seesaws between different virus species.But this protection carries a price – it makes us vulnerable to HIV. Over the course of primate evolution, humans made an important change in the amino acid sequence of TRIM5α that allowed the protein to fight off PtERV1. When Kaiser changed the protein back to its original form, she found that it gained the ability to fight off HIV, but lost its resistance to PtERV1.

In fact, Kaiser found that no primate species has a version of TRIM5α capable of fighting off both viruses at the same time. We are resistant to ptERV1 and vulnerable to HIV, but chimps, gorillas, baboons and rhesus macaques show the reverse strengths and weaknesses.

When it comes to retrovirus immunity, there is no win-win situation. Having defeated one enemy, we have unwittingly made ourselves more vulnerable to another.

Reference: Kaiser, Malik & Emerman. 2007. Restriction of an extinct retrovirus by the human TRIM5a antiviral protein. Science 316:1756 – 1758.

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Inner ear size can predict a mammal’s agility

The semicircular canals of an animal’s inner ear controls its sense of balance. Their size can tell us whether an animal is slow and ponderous or fast and agile. They can even help us to reconstruct the behaviour of extinct species.

Studying the way an animal moves by looking at its ears might seem like a poorly thought-out strategy. After all, short of watching it directly, most biologists would choose to look at more obvious traits like tracks, or limb bones.

But while an animal’s limbs may drive it forward, its inner ear makes sure that it doesn’t immediately fall over. By controlling balance, it plays a key role in movement, and its relative size can tell us about how agile an animal is.

Organs of balanceA 3-D reconstruction of a baboon’s skull and its semicircular canals.

When we walk, the image that forms on our retinas changes quite considerably. But no matter how fast or erratically we move, our view of the world neither jerks nor judders. It’s all stable images and smooth transitions, and the inner ear plays a large role in that.

In the inner ear, three semicircular canals control our balance by acting like small gyroscopes. The canals are bony, fluid-filled tubes arranged at right angles to each other and send information to the brain about the body’s orientation.

When the body moves, so does the fluid and this sloshing is sensed by hairs in the canals and relayed to the brain. The muscles of the neck and eye tense reflexively in response to these signals, and these help to stabilise our view of the world.

In humans, the inner ear doesn’t really have to work too hard – we’re limited to moving on the ground, and not very quickly at that. It’s a whole different story for a fast and agile animal like a bat, twisting and turning in three-dimensional airspace while avoiding obstacles and predators.

Acrobatics vs. stealth

Fred Spoor from University College London and colleagues from around the world reasoned that these different movement styles must be reflected in the size of a species’ balance organs. There is some evidence for this already – the practically immobile sloths have small semicircular canals, while manoeuvrable birds have relatively large ones.

But these findings seem almost anecdotal compared to the massive amount of data that Spoor collected. His group looked at the canals of 91 different species of primates, representing all the major families.

Primates have a wide range of movement styles from the fast siamang (top) to the slow loris (bottom).The primates are an ideal group for this type of analysis – despite being closely related, they have a vast range of different movement styles.

Acrobatic gibbons swing through jungle canopies at high speed using ball-and-socket-jointed wrists (top). At the other end of the spectrum, the appropriately named slow loris is a ponderous and stealthy climber (bottom).

The group used a special CT scanner, a hundred times more sensitive than those used by hospitals, to build detailed 3-D reconstructions of the skull of each species, and the three canals inside. As well as the primates, they also looked at 119 other mammals, from mouse to elephant, and gave each one a score from one to six, based on how swift or agile they were.

Canal size predicts agility

As predicted, they found that the canals of agile animals with fast, jerky movements like tarsiers (image below, left) are larger for their body size and more strongly curved. Slower species like lorises have relatively small and less curved canals.

The semicircular canals of a tarsier (left) are relatively larger than those of the Palaeopropithecus (right).Spoor’s data suggests that the size of the semicircular canals are an important adaptation to give fast-moving animals greater stability.

It explains why some primates can gracefully race through dense treetops at speeds where humans, with out relatively smaller canals, would embarrassingly collide with a branch. Just look at this amazing video from the Life of Mammals, of various lemurs (and their predators) moving through the trees.

This method can also be used forensically, to recreate the movement styles of extinct mammals. To prove this principle, Spoor looked at the canals of several species of extinct lemur, and found that their canals gave important clues about their behaviour.

Of the species he looked at, Palaeopropithecus (image above, right) had by far the smallest canals for its size. Accordingly, palaeontologists believed it was the lemur equivalent of a sloth; its hands and feet are curved for hanging from branches, and its wrists and ankles have lost the flexibility needed for effective walking.

Reference: Spoor, Garland, Krovitz, Ryan, Silcox & Walker. 2007. The primate semicircular canal system and locomotion. PNAS doi/10.1073/pnas.0704250104

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Images: Top and bottom images from Alan Walker lab, Penn State, siamang by William H Calvin, loris by Sandilya Theuerkauf

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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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Monkeys (and their neurons) are calculating statisticians

Using a simple psychological test, scientists have found that monkeys can use simple statistical calculations to make decisions. They even managed to catch individual neurons in the act of computing.

Say the word ‘statistician’ and most people might think of an intelligent but reclusive person, probably working in a darkened room and almost certainly wearing glasses. But a new study shows that a monkey in front of a monitor can make a reasonably good statistician too.

Rhesus macaques can compute statistics in a simple psychological task.Tianming Yang and Michael Shadlen from the University of Washington found that rhesus macaques can perform simple statistical calculations, and even watched their neurons doing it.

Psychologists often train animals to learn simple tasks, where the right choice earns them a reward and the wrong one leaves them empty-handed or punished. But real life, of course, is not like that.

Mostly, there are risks and probabilities in lieu of guarantees or right answers. Animals must weigh up the available information, often from multiple sources, and decide on the course of action most likely to work out in their favour.

A simple psychological test

Yang and Shadlen tested this decision-making ability in two rhesus macaques using a variation of the well-known weather prediction task used to test human volunteers. In the human version, people are shown a series of cards that represent various probabilities of good or bad weather. After some training, they are shown combinations and asked to predict the likely weather from these.

The monkeys had a slightly simpler task – they had to look at either a green or a red target. If they picked the right one (which changed from trial to trial), they were rewarded with a tasty drink. To help the monkeys choose, Yang and Shadlen showed them a series of shapes that represented the probability that the rewarding target was red or green.

For example, a square strongly indicated that the red target was the rewarding one, while a triangle strongly favoured the green one, and an hourglass only slightly favoured the green. The monkeys were shown four shapes out of a possible ten, and to get the right answer, they had to add up the probabilities indicated by these shapes.

Monkey see, monkey decide

Yang and Shadlen saw individual neurons performing computations.And that is exactly what they did. They learned to base their decisions on the combined probabilities of the four shapes, and chose the appropriate target. It did, however, take them a while to learn (or two months of training with over 130,000 trials to be exact). Any statisticians reading this don’t need to fear about being replaced by monkeys any time soon.

They weighed up the strength of the evidence too. When the shapes strongly suggested one colour, the monkeys almost always went with that colour. When the summed probability lay between the two extremes, they chose either target but still favoured the one indicated by the shapes.

With 715 different combinations of shapes, the experiment’s design makes it highly unlikely that the monkeys simply memorised the ‘answers’ for different mixes. And because the shapes only dealt in probabilities, it was still possible to choose the wrong target, even if the monkey strictly adhered to the shapes’ advice. They were clearly reasoning with probabilities, and in pretty subtle ways.

Calculating neurons

For their next trick, Yang and Shadlen visualised this reasoning directly by looking at 64 neurons in the monkeys’ lateral intraparietal area (LIP). This part of the brain is responsible for several higher functions like mathematical skills. Other studies have found that the LIP collects data from the visual cortex, and helps to process what the monkey sees.

Monkeys can calculate the sums of different probabilities.When the monkeys saw a shape, the activity of their LIP neurons was proportional to the probability indicated by that shape. As the four shapes were shown in sequence, the neurons altered their rate of firing to account for the new information. As the evidence was building up, the monkeys were busy doing sums in their heads. Yang and Shadlen were seeing arithmetic in action.

Of course, monkeys are living things and not fuzzy calculators, and they were not equally good at statistical reasoning. One was clearly better than the other, and Yang and Shadlen put this down to differences in their neurons.

Each neuron varies slightly in its typical firing rate, and summed together, these variations can lead to biases in how the monkeys deal with calculations. This explains why the monkeys sometimes did different things when shown the same combination of shapes.

Their confusion was particularly apparent when the shapes gave no strong inclination to pick one target or another. We can certainly relate to that – after all, it’s certainly harder to make a decision, when neither option seems particularly better than the other.

Yang and Shadlen believe that human brains use similar methods to make decisions. Cues about probabilities are funnelled into the brain’s control centres (like the LIP), which act like calculators powered by the firing of neurons.

Reference: Yang & Shadlen. 2007. Probabilistic reasoning by neurons. Nature (doi:10.1038/nature05852)

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