This BBC podcast is supported by ads outside the UK. It's time to see what you can accomplish with Shopify by your side. So, we can now listen to your podcast. me a rectangular block and I'm trying to pick it up using my new thumb. If you want to hear what this robotic thumb can do, stay tuned. Yes. But I think we need to start with this week's question, which is about real flesh and bone thumbs and comes from listener Lania in New York. My question is, if opposable thumbs offer such a distinct evolutionary advantage, then why don't more species have them? Okay, I know there's a story that inspired you to write to CrowdScience. Tell me about this. It all started when I was out sea kayaking, cut my thumb, and then over the next week I was struck by how much of an impact not having the use of my right thumb was. I couldn't button my shirt. I had difficulty tying my shoelace and money. I had difficulty typing on my phone. So normally I hold it in my hand using my two thumbs to type. You're a double thumb typer. How did you cope? I ended up holding the phone in my right hand, pecking away with my left index finger, and it was not a good look. You know, the thumb's a nice invention. It gives us an advantage in so many ways, not only using the phone and buttoning one shirt, but tools and other helpful things like that. So it got me thinking, why don't other species have it? And I knew exactly where to go. Yes! Yes, the smart people at CrowdScience. I'm happy to report Lanier's thumb is fully healed and he's back to his usual typing technique. Of course, not everyone has thumbs and people with limb differences have ways of making their own set-up work. But as Lanier discovered, thumbs are incredibly useful for those of us who have them. Why didn't more animals evolve them? Before we look into why animals don't have thumbs, let's figure out why we do. My name is Tracey Kivel. I work at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. And I'm a paleoanthropologist, which means I study the human fossil record and I have a particular interest in the evolution of the human and primate hand. So first of all the basics what is a thumb? Your thumb is one of your five digits on your hand but it's sort of divergent it sticks out from the side of your hand it has one less bone than we have in our fingers and it's more mobile than our other fingers and stronger. And just to check what's an a poseable thumb. Yeah. So poseable, this is a word that we use to describe the fact that we can move our thumb towards the tips of our fingers. And in particular in humans, that we can do that with the pad of our thumb towards the pads of our fingers. Like when you're pinching a key, for example, or holding a pen. I've never really noticed it before, but I'm just trying to pinch between two of my fingers and it's not working for me. Opposable thumbs, useful. Are they uniquely human? No, they're not. Most other primates also have opposable thumbs. So chimpanzees, gorillas, orangutans, most monkeys that live in Africa and Asia, and even some monkeys that live in South and Central America also have semi-opposable thumbs. And how did we get our thumbs? Did our early primate ancestors have opposable thumbs too. Yes, so these sort of five digits is something that goes really far back into our evolution. That's sort of the ground plan for almost all mammals. Some of the earliest primates are from a period called the Eocene, which is around 55 million years ago. And this is when we start seeing the first primate hand with these five digits and a thumb that is at least divergent from the rest of the digits. And before then, it would just be like five basic fingers that hadn't differentiated. Yeah, they'd be more, if you think like a raccoon, for example, that actually is really still quite dexterous. If you've ever seen a raccoon in your rubbish, they're very good at getting into those things. Trash pandas. Exactly. But they have short fingers lined up in the same direction. We have, or primates in general, have this divergent thumb as well as quite long fingers that we can move semi-independently as well. So the first primates don't look like the primates we see today. They really look a little bit more like squirrels or opossums. This is at a time, I also remember, right after dinosaurs go extinct and there's open niches for which mammals can now explore because dinosaurs are gone. And primates are one of those. So they started off very tiny. And the first times that we see a primate like hand is in something that's really quite small, probably spent most of its time in the trees. And those long fingers and a divergent thumb was probably really useful for grasping branches and grasping branches of different sizes. And especially those really small ones at the ends of tree branches where flowers and fruits grow. And so one of the hypotheses is that that's why primates are known for being dexterous or having these grasping hands because they needed them to access these foods at the ends of the branches and trees that other mammals at the time couldn't access. That gives you a clear calorie advantage Yes exactly I can see how that would work for evolution So that a good guess or to be scientific reasonable hypothesis behind how monkeys got their thumbs Any proto-primates with thumbs could pluck more fruit, eat more and be more likely to live long, healthy lives with lots of offspring, who would also inherit that useful thumb trait. Other animals, whose lives didn't involve tree climbing and fruit picking, didn't have the same evolutionary pressure. But primates, that's monkeys and apes, aren't unique in finding a thumb useful. So we can stand quite close to him. Hi Humphrey. Tens of millions of years ago, Humphrey's ancestors were figuring out the best plan for their hands. and today we've come to meet him in his native country. We are currently standing in Humphrey's habitat and Humphrey is one of our beautiful male koalas. We're at Taronga Zoo in Sydney, Australia with Humphrey and senior keeper Taryn Williams-Clough. Hello Humphrey. I'm slightly in love with you. I think we all have a bit of a soft spot for Humphrey. He is a very sweet-natured boy and luckily he's awake. Most of the time he's actually snoozing so we've come at a really good time. Humphrey is on a perch just at head height and he's just turned his head to check out what we're doing. Now, we wanted to meet a koala because our listener has asked why more animals don't have opposable thumbs. And I think Humphrey here has, is it two on each hand? He's two. Very well suited to life in the trees. And excitingly, he's on the move. So he's going to show you exactly how he uses those two opposable thumbs as well. They're both on the same side. I thought it would be like, here's a thumb on one end and here's a thumb on the other end. But it is literally two thumbs next door to each other. If you have a look at our hands, it's essentially more like the index finger has evolved to continue wrapping around to join that thumb. And you can see what a vice grip he has on that branch now and how easily he can hang on. So it keeps him up nice and safe up in the treetops. He is going to use that for his food as well. So they are incredibly selective with what they eat. They only eat eucalyptus leaves. Now having those opposable thumbs is going to help him be able to select the very best leaves, figure out which ones are the most nutritious and the least toxic and bring them to his mouth. Humphrey's just sneezed. It's not a bad life, Humphrey, is it? Not a bad life. Koalas are marsupials. It's a hugely diverse group of mammals, and there are a few other marsupials who evolved opposable digits. But interestingly, most of them didn't. I'm off to meet one that took a different route and never developed thumbs. Why not? Ooh, it smells like stables. Oh yeah, well they eat mostly hay. In another corner of Taronga Zoo, senior keeper Bec Russell Cook introduces me to the koala's closest living relatives. wombats. That's the mum, her name's Jetta. They're very sweet. There's an exciting mixture of pig, hippo, mid-sized dog, short legs, but also rabbit. You don't get much of a koala vibe when you look at them. But they are the closest relative to the koala, right? They are, yes. They share a common ancestor. The wombats stayed on the ground and evolved to live underground and they eat mostly grass, sometimes roots as well. So you would have seen her claws. They're quite thick, large, stocky front feet. And that's so they can dig their burrows and dig up their food as well. And crucially, something they do not share with koalas is thumbs. Yes, they do not have an opposable thumb because they don't need to climb. They've just got five stocky, sharp-clawed spade leg toes. Perfect for digging. Perfect for digging, yes. She's walking towards us slowly and just stopped for a belly scratch with one of her front paws. Yeah, and from what I can see, they're all forward-facing toes. And you'll see as well her back feet do look quite different to the front feet. They're a bit pigeon-toed and that helps when they dig with their front stocky feet and then they'll kick the rest of that soil out with those little back toes. She's just gone outside into the digging yard. Do you want to pop outside? Hello, Chonky Girl. She does love digging, so there we go. Oh, brilliant. She's done exactly what you said. Yeah. Dig with the front, kick out with the back. Yeah. Oh, yeah. Good digging. She's in the digging zone. Koalas and wombats are equally delightful, but so different. They're each other's closest relatives, and yet one ended up in a tree with multiple thumbs, the other, in burrows, with a set of impressive spade-like digits, but no thumbs. So what do we know about their evolutionary history? Koalas belong to this big group of now mainly extinct marsupials called Wombatiformes, which include the wombats, as you may have guessed. The only survivors of that whole group are the koala and the wombat. This is Mark Eldridge, a research scientist at the Australian Museum in Sydney, who specialises in marsupials. Koalas and wombats diverged about 30 to 40 million years ago, but we have virtually no fossils to know what was going on in the common ancestor. We just know that out of this basically terrestrial quadrupedal group, we now have an arboreal specialist. I.e. the koala. It seems likely that the koala wombat common ancestor was more wombat-like, at least in that it was quadrupedal or walked on all fours. Mark has a stuffed wombat and a stuffed koala on the table next to us but frustratingly there isn't a good fossil record of their evolutionary journeys. However, he does have a hypothesis for why the koala has not one but two thumbs. I think one of the key things is this group basically lost its tail when they were quadrupedal on the ground but then the koala became arboreal and I suspect this might be why you haven't got the tail for balance you haven't got a tail for prehensile gripping like other possums do and other animals do so you really if you're going to hang on to branches you really need to make sure you can hang on to branches yeah and so they've come up with this solution of well if you actually have two digits on this side and three on that side you can actually have a really firm grip onto a branch and compensate so wait the The koala's thumb adaptation might be because it lost its tail, and so it couldn't use its tail to grip onto a branch, and so it needed a better solution from its thumbs? That's my hypothesis. And, you know, I think it's reasonable. They do have a tail. They've got this tiny little tail about this long. Okay. But they're functionally tailess. Like humans. Yes, yes. Talking of humans, I'm going to put my hand out here next to the koalas. And can you point out the similarities and differences that we got Well the main similarity is the five digits We have one opposable thumb they have evolved two opposable thumbs Also the claws which are very long and very recurved. Yeah they're like little grappling hooks. They are and weirdly koalas also have fingerprints. Is that weird? It is weird. Very few animals have fingerprints and again we believe this is to aid grip to branches but also to help them do lots of really fine-scale manipulation of eucalypt leaves. Koalas are super fussy eaters, as you probably heard. Feeding is quite a laborious process for a koala. Being that picky, I have to say, doesn't sound like a great evolutionary adaptation. Have they considered just eating more sort of wide variety of stuff? The trick is, because eucalypts dominate the Australian landscape, you're not going to be necessarily short of food if you can work out how to eat gum leaves. But you have to overcome all these issues, all the toxins, all the low nitrogen, low water content. But if you can overcome those, then you've got very little competition and you've got, you know, a banquet. Delicious, low protein, toxic banquet. It's amazing no one else claimed that niche. Eating only eucalyptus, koalas ecological niche is highly specialised, so their thumbs have very particular uses compared to humans' multi-purpose tools. Now, I realise we've been distracted by animals with thumbs. And while humans are by no means unique, the majority of animals don't have thumbs. Why aren't they more common? We're about to find out. Starting a business can be overwhelming. You're juggling multiple roles, designer, marketer, logistics manager, all while bringing your vision to life. Shopify helps millions of business sell online. Build fast with templates and AI descriptions and photos, inventory and shipping. Sign up for your one euro per month trial and start selling today at Shopify.nl. That's Shopify.nl. It's time to see what you can accomplish with Shopify by your side. I know you want to listen to your podcast, so I'll keep it short. Because if you think it's important to make a choice, can ASR maybe help? Well, I think, how then? Well, for example, when you're doing a lot of things that are you love to do. Will you know more about the insurance where a lot of schade can be? Go to asr.nl slash duurzamekeuzes. This does ASR for you and a healthy family. ASR does it. So, we can now listen to your podcast. I think it would love one. Here's paleoanthropologist Tracy Kivel again. The trash pandas would do even better in getting into our rubbish bins if they had them. Oh, wow. They'd take over the world. They'd unpick locks. They'd probably drive off in cars. Exactly. But our listener was thinking, wouldn't there be a strong evolutionary pressure for more animals like raccoons, like any other animal, to develop a thumb? Why haven't they? It's a great question. It's part of, you know, manipulation or being able to access new foods, whether it be fruits at the ends of trees or using a stone tool to cut into a carcass or something like this is really important part of the human evolutionary story and of the primate evolutionary story. But for many other mammals, it's not important. They have teeth that allow them to access those foods. Or they need hands that have claws and have short fingers that are really good for climbing on tree trunks, for example, if you think of a squirrel. And if they didn't have that morphology, they wouldn't be good at doing what they need to do. That's what always amazes me and why I love my job is that I'm always like, wow, that's a clever way of solving that problem that I wouldn't thought of through the process of natural selection. Natural selection is when a variation within a population gives those with it a higher chance of surviving, reproducing and passing on the genes that caused that variation, which means that millions of animals have millions of adaptations that give them exactly the hands they need to survive and thrive in the lives they live. For a wombat, that's a tool for shoveling dirt. For a hawk, that's a claw for grabbing its prey. If a thumb is an important part of that, you'll probably see it. But it doesn't have a monopoly on any function. Yes, it's useful for grasping, but so is an elephant's trunk, or a snake's prehensile tail. In fact, some animals have found it useful to lose digits. Generally, primates are more dexterous than what we see in other mammals, for example. But there are many examples today of like spider monkeys, for example, that no longer have thumbs or the thumbs that they have are really just tiny and useless. The adaptive potential reason for that is that spider monkeys spend a lot of time in the trees, particularly suspending from branches, and that thumb just sort of gets in the way. And so they've gotten rid of it. Can I broaden it out into feet? Because we don't have opposable toes, right? Yeah, so this is one of the things that is really quite unique about humans. When you look at gorillas or chimps or most other primates, just like they have grasping hands, they also have grasping feet. So they have big toes that are also divergent from the rest of the digits. Humans don't have this, as you know. So your big toe is now in line with all your other toes. And that is really just related to bipedalism. So walking on two feet. So it's a process of evolution. Well, our big toe became less and less good at grasping and now is really good at walking and at running. While other apes' toes are optimised for grasping, human feet have something in common with running animals like horses, cheetahs and dogs, all thumbless. It looks like thumbs don't lend themselves to an elegant sprinting style. And once we were up on our feet with our neat, newly aligned, non-grasping toes, how did that affect the evolution of our hands, thumbs and even brains? So the main things that we think drive the evolution of human hands is the fact that we have at some point during our evolution stopped using our hands for climbing or locomoting. And then the other main driver in that story is tool use. And so that using stone tools enhanced our dexterity and really made us have these powerful opposable thumbs The human thumb is actually really quite big compared to our closest living relatives so chimps and gorillas. So we're holding up models of a chimpanzee and a gorilla hand. Oh, they're huge. And so they have these amazing huge hands, but these tiny little thumbs relative to the length of their palms and their fingers. But if you look at your own hand, your thumb is actually quite long. and that gives us more ability to sort of hold objects either forcefully or doing things that require a lot of precision. And the longer your thumb, the better you usually are at doing these kinds of precision manipulation tasks. So can you join the dots? Can you say walking feet, freed up hands, therefore that built our brains because we were using our brains differently? Can we link them that way? I think in a general sense, yes. At least when we have the stone tool evidence, we can say, oh, they were using that stone tool to cut up bones, which means they're probably cutting meat or they're pounding the bones in order to get it marrow. And those are really great sources of calories and protein. And that would fuel a bigger brain. And then when you have a bigger brain, you can make better tools. And it's all nice positive feedback loop is a simplified version of that story. but I think is generally true. It's just figuring out the exact pathway is a much more difficult question to answer. The particularly nimble human thumb seems to go hand in hand with our large brains, which perhaps helps explain why no other animal has a thumb quite like ours. And they certainly haven't made one like this. It's an extra robotic thumb made to extend the function of any hint. This is Dani Claude, who you heard at the start of the show. She designs prosthetics and augmentation devices and brought one into the CrowdScience studio for me to try. The third thumb. I can't control the speed of this. Like a koala, I now have two opposable thumbs on my right hand, one fleshy living one and one made of grey plastic segments held together with fishing lines. Unlike a koala's, my second thumb isn't next to the first It's on the opposite side, next to my little finger Oh, not quite It's controlled by signals sent from sensor pads by my two big toes So the right toe is doing this movement So if you imagine your thumb kind of pulling across your palm And then the left toe is pushing up towards the digits And then if you use them together You can kind of diagonally pull the thumb across your hand Oh, OK, so you have to steer it with a combination of both your big toes. Yeah, so it's, yeah. I'm now playing thumb war with my fingers accidentally. Come on. I made it during my master's degree at the Royal College of Art in London. I was designing prosthetic arms at the time and wanted to explore what it was like to wear it like a piece of technology that's responding to my body's movements. And I wanted to really focus on recreating the movement of the human thumb. The new thumb expands the function of my hand. I'm going to pick up this squeezy bottle. For example, I can use it to grip an object in my palm, freeing up the rest of my digits. And I open the lid. Probably want to grip with the third thumb. Yay! Training people to use the thumb is now part of Dani's job, after some neuroscientists picked up on her invention. There were neuroscientists studying upper limb difference in the brain, so people born with one arm, people born with no arms, high-level prosthetic users, phantom pain, all of these things in the brain. And they also thought, what if we add to the arms? How does the brain respond to that? And then saw the third thumb and they were like, do you want to work together? The scientists were from the plasticity lab run by Professor Tamar Makin, now at the University of Cambridge in the UK, but back then at University College London. So we used the third thumb as a model for human augmentation and to explore kind of how the brain adapts when the body's abilities change. We did a five-day training study with participants. So we did an IFMRI, so functional MRI, before they used the third thumb, and then five days of training, and then a functional MRI after the five days. They did two hours of training with the third thumb every day, and then also they got to take it home with them and just use it at home. The participants had one hand augmented with the extra thumb, while the other carried on as normal. After just five days, the effect of an extra thumb actually showed up in brain scans. We saw a slight change in the brain in how their fingers were represented in their hand area of that augmented hand compared to their non-augmented hand. It was a small effect and disappeared when they tested again after five days of not using the thumb. But it suggests that although our thumbs and brains co-evolved over millions of years, our brains are flexible enough to adapt to using an extra thumb. Some people even started to feel a bit like it was a part of them. We do an embodiment questionnaire. Questions like, I feel like I'm looking at my own thumb. I feel like it's a part of me. And we were actually quite surprised that they did start to swing upwards, you know, towards feeling slightly more embodied over the third thumb across the five days. You know, just kind of taking it off at the end of the week as well. I feel quite bad. I had one girl who was just like, can I just have a moment to say goodbye? And I'm like, sure, babe. Thumbs are so useful that having another one just feels like a bonus. So obviously this particular thumb is an invention, not evolution. But as for why more animals didn't evolve one at all, there are as many stories as there are animals. Living in trees is a common theme, but even here, some monkeys have evolved to lose their thumbs. And when we humans moved to life on the ground, we still found the thumbs on our hands immensely useful for working with tools. Foot thumbs, less so. And so, out they went. That's evolution in action. Use it or lose it. Thumbs up to listener Lanier for the question and back to him for the credits. That's all for this episode of CrowdScience from the BBC World Service. The question came from me, Lanier, in New York and the show was presented by Marnie Chesterton and produced by Cathy Edwards. If you have a science question, whether inspired by personal misfortune or not, Please send it to crowdscience at bbc.co.uk. Thanks for listening. Bye. and precisely the same dose of sarcasm. Bingo. BBCNL, the place for the best British misdaad series. Just on your NEDELANDSE TV.
