A (3:15)

But can we really understand what a primate is thinking? We can't communicate with chimps. So how does Katie study them?

B (3:24)

A lot of human psychology work, you ask people questionnaires, don't you? Obviously, we don't share a common communication system with chimpanzees and so we can't ask them directly. What do you think about this? What do you like? We just can't do that. But it's the same struggle that developmental psychologists have. So when you're working with preverbal infants, you're still trying to work out what's going on in their mind, but you can't ask them things. So what we have to rely on for both chimpanzees and preverbal infants is behaviour. So we have to look at their behaviour and then try and think about ways that their behaviour can tell us what's going on in their mind.

A (4:06)

Now, I would argue that you also need to study the behaviour of humans to learn what they think, as we often can't trust what humans say. But anyway, I asked Katie for an example of this in chimp behavior. I asked her how she has studied chimps to reveal what they think.

B (4:21)

So a lot of my work, which is focused mainly on communication has been through spending time in the forest in Uganda with the chimpanzees and observing them. And I've seen something really interesting. So that's what we call an anecdote. So I've just seen this one off instance, this interaction between individuals that sparked my interest and I thought, oh, why on earth did they do that? That was really interesting. So an example where this happened, we're in the forest following a female who was in full oestrus, so that means that she's Receptive for mating. So very attractive female. She'd had multiple previous infants, so very valuable mating partner for the males. So the males were all over, kind of surrounding her and it's quite a stressful time for the female, all the big males. So she mated with several of the big males in the morning and then they'd all gone up into a tree to feed. The males then got a bit distracted by the food and the female had had enough to eat. She came down, back to the ground and we followed her. And away from the tree she met a low ranking male who was very insistent that he should be allowed to copulate with her. And she just didn't want anything to do with him. But rather than just kind of running away, she started screaming as if he was attacking her brutally. He wasn't touching her. Those big males came down from that tree incredibly fast, displaying, chucking things, drumming on trees, and that low ranking male screamed and ran for his life essentially. And I thought, ooh, that was naughty, you were lying, that was deceptive. He was not attacking you when you screamed like you were being attacked. And so it got me to think, you know, maybe they are sometimes using their screams deceptively. So we then went about systematically recording lots and lots of fights and lots of, lots of getting audio recordings of the screams and detailing exactly what was happening every time the chimpanzees were screamed. So that's the kind of detailed, systematic observational data I collected. And from that we found that when the aggression is severe, so if they are being kind of singled out by an aggressor or they're being physically attacked, if there is an individual in the auto audience who can help them by stopping the attacker because they're higher ranking than the attacker, then they will exaggerate the severity of the aggression. So they will scream as if it's even worse than it is. So their screams will be longer and they'll be higher pitched than if there's not someone there that can help them.

A (6:56)

Katie's work revealed that chimps can use their screams in a tactical way to deceive others. And she's proven this in the wild.

B (7:04)

When it comes to experiments where you're able to kind of manipulate things to test your ideas much more concretely, I have to say it's much easier to come to captivity to do that. So it's much easier to then work with chimpanzees in zoos or sanctuaries. And I have also done that, but I have also tried to do experiments in the wild. Where the conditions are a lot, lot more challenging. But I think the results are probably more meaningful.

A (7:29)

You might be wondering exactly how much chimps can communicate. How do they collaborate and do they have a shared langu, for example? Well, I asked Katie.

B (7:39)

For me, language is a very human specific term. So language is a very special way that we have of communicating, which I do believe is unique to us. But chimpanzees still communicate a huge amount of information to each other. So in terms of their vocalizations, they tend to communicate about food. So that's a kind of key area that they communicate about. And the rest, really, mainly they also communicate about dangerous things. So they have alarm calls and then a lot. Most of the rest are really to facilitate social interaction. So we've got the screams that they give when they're fighting, We've got the pank grunt, which is a very important information giver in terms of the hierarchy. So this is a vocalization that subordinate chimpanzees give to their dominant individuals. And it's a sign of respect and submission to them. So again, that's very important for kind of, you know, oiling the wheels of chimpanzee society. And then you've got another array of kind of different grunts that they give in different situations. And again, there are some vocalizations which we don't have a good handle yet on, really what they mean. We've got then long distance communication. So the males particularly give pant hoot vocalizations. Which help them communicate, you know, over several hundred meters of forest to other chimpanzees. They give information about identity, so they are individually distinctive. So just as you may recognize my voice next time you hear me and I would recognize yours, the chimpanzees are the same, so they know exactly who is who just from their vocalizations.

A (9:33)

Later in the episode, we'll cover what those communications can teach us about human communication. But first we need to cover another chimpanzee behaviour that is also visible in human power.

B (9:46)

So in chimpanzees, there is a really clear power structure and particularly for the males. So in the males, adult males have a linear dominance hierarchy. So it's always clear who is dominant to who. And we use that pank. As researchers, that pankrump vocalization is our main tool for working out who is where in that hierarchy. So if chimpanzee A pank runts to chimpanzee B, A is definitely below B. And so if you can record enough pankrunts, you can work out exactly who is where in that hierarchy.

A (10:21)

Katie's work highlights how the vast majority of communication between chimps is to assert power structures. But why do chimps care so much about power? And what advantages does a high powered chimp get?

B (10:35)

There's lots of advantages to being top of that hierarchy and being powerful in chimpanzee society. So we know from research that the dominant males tend to get feeding spots higher in the tree where the sun has ripened the fruit. And presumably they have a higher sugar content, so they likely get more calorific food being able to displace others from those best places in the tree. Although females aim to disguise paternity by mating with multiple males to reduce the risk of infanticide, high ranking males always get kind of priority for mating with receptive, attractive females. And all of the long term study sites show that that translates through into you father more children. High ranking males end up with more offspring than the low ranking males. So a lot of the low ranking individuals spend a lot of their time grooming higher ranking individuals to try and make friends with them. So it's a high ranking individual you get groomed, that's removing parasites, but it's also getting a huge amount of endorphin release which reduces stress levels, which again has physiological benefits. They also are more likely to get hold of meat. So if they, if there's a successful hunt of a monkey or an antelope, the high ranking individuals are more likely to get a share of the meat whether or not they kind of participated in the hunt. And finally, and I think this for me is the most human bit, like it gets you respect, it gets you a lot of individuals coming up to you and going, I know people who like to feel respected and like being able to kind of induce that reaction in others.

A (12:19)

There are lots of similarities between human and chimp power structures. High powered chimps get better food, a wider choice of partners and a lot of respect. Very similar to human power structures. But how do chimps gain this high power? I asked Katie.

B (12:35)

There's kind of two main strategies, but each of those strategies there's multiple things that they'll do. So the first strategy is brawn. So physical intimidation and aggression. And so male chimpanzees spend a lot of time doing intimidation displays as an observer on the ground. They are really intimidating. They can either do them silently or they'll combine them with a panthoot vocalization which is in itself very loud, but they will go pilo erect, so they'll make all their hair stand on ends, which kind of makes them look double as big. And then they will charge through the forest and they will ground slap, they'll drum on the trees with their feet, they will throw things. They do that to try and kind of intimidate others and to show how strong they are, they will supplement that with then direct aggression. So they will then single out individuals and they will chase them, they will beat them, they'll pick them up and throw them against the ground. Ultimately they, you know, if it gets to biting, that can be really serious. So again, you know, chimpanzee aggression can be really serious and horrible.

A (13:46)

However, high powered chimps don't just use disaggression against everyone, they are tactical with

B (13:52)

who they choose to direct that aggression towards. So if you've got two quite equally ranked males, so say you've got kind of a second and third ranking male who are vying to become the next alpha, it's very unlikely that the second and third male would take each other on. So we had this situation in the community. I did my PhD work in with Nick and Zephyr and they never fought each other directly but Nick did kind of showcase beatings of others in front of Zephyr where he would pick maybe the seventh ranked male and he would really pummel him, bite him, injure him quite badly. And as a kind of like, yeah, look at that, you don't want that to happen to you, do you?

A (14:34)

That's the physical way to gain power. And Katie makes the point that the biggest and strongest chimps tend to gain the most power. But brawn alone is not enough to rise through the power structure. Chimps need another skill.

B (14:48)

If you can make a coalition with other males, then that can then really help elevate your rank. Because if you've got two individuals, even if they are individually less strong than the ones above, if you're going to work together and back each other, then two chimps are always going to beat one chimp. You can create that really close bond with another chimpanzee, then you stand a chance of really climbing up the hierarchy. And so to make that bond with another individual, you need to invest time into grooming with them. As we said, that's, you know, it does fulfill a cleaning function to remove parasites, but it's basically a social bonding tool. You then expect that those individuals would support each other in fights, building up to them, being able to display together and then eventually fight those above you to become more dominant to them. If one of you catches a monkey, you would share that meat preferentially with that partner, those individuals that you're close to, you would advertise. If you find a good food tree, you would advertise that good food tree to those high ranking partners. Those are the kind of behaviors that you would do to kind of try and form those coalitionary partnerships with other male chimpanzees. So if I look at the kind of alpha males that I've known, the most successful ones are the ones who have really invested in that relationship building as well as being big and strong. And the ones who were just big and strong and got there through fear and intimidation alone have lasted a fraction of the time.

A (16:25)

To become a high powered chimpanzee, the primates need to show a mix of strength and social skills. But social skills alone are not enough.

B (16:35)

I've never known, like a weedy alpha male, you have to have a baseline of kind of physical strength for those intimidation displays to be effective. Probably the best example of why that's so is that there are some individuals who sadly suffered from snare injuries when they were younger.

A (16:53)

I should mention that a snare injury is when a chimpanzee becomes trapped in a wire or rope loop set by a human hunter. This sadly causes deep limb wounds that restrict movement and can lead to infection or in many cases, amputation.

B (17:08)

So, for instance, Kanuara, there's a chimpanzee called Max who has lost both of his feet through snares. He does amazingly well considering he has to walk on two stumps. But he is going to be low ranking his whole life. However clever and however good he is at relationship building, which has probably kept him alive to now, he's always going to be low ranking.

A (17:30)

So far, Katie walked through how chimps communicate, why they desire power, how to get it, and what is needed to stay at the top of that power structure. After this short break, we will cover much more. Firstly, Katie will walk through one of her fascinating studies which showed how chimps decide whether or not to share food. And then we cover what Katie's time spent studying chimps taught her about humans. All of that coming up. The podcast I'd like to recommend to you today after you finish listening to Nudge, is the Hustle Daily Show. It is brought to you by the HubSpot Podcast Network, the audio destination for business professionals. The Hustle Daily show brings you a very healthy dose of irreverent, offbeat and informative takes on business and tech news. If you'd like an interesting episode to get you hooked on this podcast, there's a recent Episode called the AI app that makes your dream vacation a digital reality. If you want to listen to that, just go and search for the Hustle Daily show, wherever you get your podcasts. Hello and welcome back. I'm talking to the brilliant professor Katie Slocombe, who has been explaining what we can learn from primates. And the biggest lesson we'll learn today is from one of Katie's own studies.

B (18:43)

Yeah, so one of the things that's really always fascinated me about chimpanzees is the vocalizations that they make related to food. Often when they find a food tree in the wild, they will give what are called these rough grunts. So these calls, but they're quite graded, so they grade from this kind of low pitched right up to really high pitched kind of tonal vocalizations. When you're with chimpanzees in the wild, they don't make it at all. Feeding trees, they make it at some point and not others. And it's always fascinated me, you know, what information is being communicated with those grunts, but also why are they doing it. This started with an anecdote in Badongo Forest in Uganda. I was with the adult male, the alpha male at that point, Duane, he climbed a relatively small tree and started feeding in it. And he was going bananas. He was giving these really, you know, calls, which generally is indicating high quality food. And he was on his own at the beginning. And then Nick and Boba turned up and they climbed up with him and fed. And he continued, he continued to call, continued to call. And eventually, after about 10 minutes, Marnie, Duane's best friend, then appeared and climbed. And it wasn't until he had climbed and then he was feeding in the same tree. And as soon as he was feeding, Duane was then silent. And I thought, oh, that really seemed very targeted at Marnie. It didn't seem like you were just being like, oh, the food is lovely. As a kind of general expression of joy, the timing of the ending of his call seems like his goal had been satisfied. And so again, that kind of triggered the idea. And I was like, okay, how can we go about actually investigating that systematically? So I then started following kind of your focal chimpanzee throughout the day. So I'd pick a male and I'd try and stay with them all day and I'd record everything that they ate and kind of all the characteristics I could about what they were eating. So the kind of how big the tree was, how tall it is, what's the crown, what's the diameter at Breast height of the trunk, is the fruit ripe? Is it fruit, is it flowers, is it leaves, is it nuts? So all the kind of ecological parts of the kind of the food source, but also critically, who was there with them? And so we collected that kind of observational data and what we found there was that when the chimpanzees grunt, so they only grunt in about half of feeding events, but when they do grunt, it tends to be on large divisible kind of fruiting trees where presumably kind of competition is not that high. And we also critically found that they're more likely to do it with individuals present that they like and that are high ranking.

A (21:39)

It's fascinating. This suggests that chimps are not just highly perceptive, only calling when the tree contains just enough fruit to share, but also that the calls are tactical and strategic. Just like humans, they choose to share with high ranking individuals to gain influence and hopefully benefit from reciprocity. Further down the line, however, Katie is quick to point out that this observational data, it isn't enough to draw lofty

B (22:05)

conclusions, but that observational data is only correlational. So all we can say is that it's more likely that when they grant there are individuals in the audience that they like and that are higher ranking, but it doesn't quite show us that they're doing it, you know, they're addressing those calls to that specific individual. So then building on that observational research, we then did experimental work and this was something that we tried, we did in the wild and it took us two years and it was really, really hard to do. So the idea of the experiment was we would follow a male until he went off on his own and started feeding. And at that point we would try and simulate for him the arrival under his tree of an individual who is either higher or lower ranking than him or a friend or a non friend to see if we could, you know, if it's a, if it's a high ranking friend, do you start grunting and do you stay silent if it's someone that you don't like or it's a low ranking individual? And so to do this we played back the pant hoot vocalization of another male in the community. So the pant hoot vocalisations are individually distinctive to. And so we were pretty sure that if we broadcast that he would think, oh, it's Bob just over there, right? Do I now basically tell him about my tree that I found and advertise it to him and allow him to come and share it with me or Do I stay silent? And so the tricky thing was obviously in the wild we have no control over where any of the chimps go. And so we had to have people with lots of different sets of chimpanzees because we needed to know where the individual was in reality whose call we were playing back because it needed to come from like a congruent direction because we think the chimps have a very good idea of where they all are in space. So if Bob is actually in the north and we play him from the south, then the feeding chimp could have been like, what, what's going on? So we have to try and make it. Any experimental manipulation like this, we have to try and trick the chimps into thinking it's real. And so that's why it took so long to get not very many trials done. But we did find kind of supporting what the observational data found, that they are more likely to start grunting when they're feeding on their own if it's a high ranking friend that they hear the call of below them than someone that they don't like or someone that's low ranking. So that really kind of for us showed all of that evidence together, showed that they are using those calls tactically and they are using them to attract into the tree with them individuals who are most useful for them. Again, going back to power in this

A (24:47)

ascent to power, I find this fascinating. I've spoken at length on Nudge about the power of reciprocity in humans, how effective it is to offer someone a favour in order to get something in return. Studies by Reagan and Cialdini show that this works in a multitude of different settings. But now Katie has also revealed that this tactical gifting, it isn't even a uniquely human trait. It is something chimps do as well. And it left me wondering how else does a chimp's behaviour, well, how else is it similar to human behaviour?

B (25:19)

My main focus has really been on chimpanzee communication. One of the reasons I'm really interested in that is to try and understand where human language evolved from. So the way that I think about it is and think, okay, well which aspects of language are uniquely human and actually which aspects of language might be and shared and therefore we might also see in the chimpanzees. When I kind of first started my research, the traditional view of vocalizations in chimpanzees was that they were very involuntary, that, you know, the chimpanzee would come across food and they just go and not really know what they were doing. You know, they just didn't have much control over it. And the more I observed them, the more I thought, I'm not sure that's totally right. And so we then did some experiments with presenting the chimpanzees in the wild with snake models to elicit alarm calls. And again, filming everything from multiple angles and getting as much information from those interactions as possible. And then we looked at, if you're producing a signal intentionally, how can you tell whether someone's doing something intentionally? Luckily for us, there's a whole literature in preverbal infant human infants, seeing how you can probably tell that they're using their gestures intentionally. And those criteria have been then applied to chimpanzee gestures, and we then applied those to the chimpanzee vocalizations. And so we found things like just before they alarm call, they look at who they're directing it to and they monitor their audience. So they don't just fixate on the snake and an alarm call, they are looking at others before they're doing it. They gaze alternate between the snake and the individuals that they're trying to communicate with. And they continued to alarm call until all others in the group were safe. So that either meant that they come and looked at the snake and they knew where it was, or they'd gone up a tree or they'd moved away from the area.

A (27:14)

Katie was helping to prove that chimp vocalisations weren't involuntary and random. Instead, they were intentional signals used to alert others.

B (27:23)

That was the first kind of indication to me that was starting to challenge this narrative that actually chimpanzees don't have any control over their vocalizations and it's all just reflexive and actually saying, well, no, actually, I think we've underestimated what they can do with their vocalizations. And again, there's a huge amount more research needed. So that's only on alarm calls. The food call stuff research that we did also kind of supports that idea that they are able to use them tactically. It's not just a stimulus response, but they give so many other vocalizations and we don't really know how intentionally given some of those vocalisations are.

A (28:02)

For me, Katie's research reveals not just how different we are from chimps, but also how similar we are. We crave power just like chimps. We deceive others in order to get what we want. We communicate strategically with those we like, ignoring those we dislike, and we reciprocate to those who give us favours. Katie has documented all of these behaviors in chimps, proving really we have more in common with them than we probably think.

B (28:29)

So there's a huge amount more to know, but I think I found that really exciting to kind of challenge an existing assumption about how we are different from chimps and actually maybe showing that in that regard we're a little bit more similar than perhaps we first imagined.

A (28:46)

That is all for today's episode of Nudge. Folks. Thank you so much for listening. And a huge, huge thank you to Professor Katie Slocombe for sharing her eye opening research on the show. If you want to learn more about human psychology, perhaps how we struggle to kick bad habits, or why we follow the actions of others, or perhaps even why we find it so hard to change our minds, then I think you'll love the Nudge newsletter. It's sent once a week on a Friday morning and it contains the very best behavioural science tip I ever discovered. That week I spent 18 hours each week researching behavioural science and I put the very best tip in my Friday newsletter. I've left a link to sign up to the newsletter in the Show Notes. It is completely free, takes less than 30 seconds to subscribe and you can unsubscribe at any time. 10,532 of you read the newsletter each Friday, and for those who sign up today using my link in the Show Notes, I'll even send you a special surprise gift. So go click that link in the Show Notes, subscribe to the newsletter and you will even get a special gift. Thank you for listening. I'm Phil Agnew and I now realise how I'm far more similar to A channel than I would like to admit. Anyway, I'll be back next Monday for another episode of Nudge. Cheers.