Why don't more animals have opposable thumbs?

On a recent kayaking trip, CrowdScience listener Lanier sliced through his right thumb, putting it out of action for a while. This made life difficult, as he couldn’t button his shirt, tie his shoelaces or type efficiently on his smartphone. Missing the use of his thumb made him wonder: since opposable thumbs are so advantageous to those of us who have them, why didn’t they evolve in more species? Host Marnie Chesterton unpicks the evolution of our own unique thumbs with the help of paleoanthropologist Tracy Kivell, learning how our grip compares to that of other animals. We discover why mammals like horses and dogs have no use for thumbs, and why we humans don’t have opposable big toes. Meanwhile, at Taronga Zoo in Sydney, Australia, senior keepers Tarryn Williams Clow and Bec Russell-Cook introduce us to two different marsupials. Humphrey the koala has not one but two thumbs on each hand. Why did koalas develop this anatomical quirk when their closest living relative, the wombat, has spade-like digits? Dr Mark Eldridge from the Australian Museum shares his hypothesis. And what if we, too, had another thumb? Marnie tries on a robotic Third Thumb, built by designer Dani Clode. Dani has collaborated with neuroscientists from the Plasticity Lab at the University of Cambridge. She tells us what the Third Thumb has revealed about the human brain and how we control our digits. Presented by Marnie Chesterton Produced by Cathy Edwards and Margaret Sessa Hawkins for the BBC World Service(Photo: Kung-Fu Koala - stock photo Credit: Alex BOISSY / Getty Images)

Noise cancelling headphones filter out sound waves that we don’t want to hear. Listener Ahmed in Libya loves wearing his and, as he was listening to them, he had a thought: ‘Could we cancel out light waves in a similar way to how noise cancelling headphones do it?’ He sent his question to CrowdScience and now presenter Alex Lathbridge is getting deep into the physics, to find out if light cancelling devices could replace curtains and shutters. Alex starts at the Ray Dolby Centre in Cambridge in the UK, built to honour Ray Dolby’s invention of noise cancelling technology. In this amazing building he meets Jeremy Baumberg, Professor of Nanophotonics at Cambridge University. With the help of a tuning fork and a laser beams, Jeremy shows Alex that manipulating light is no easy feat. Undeterred, Alex tracks down Stefan Rotter, Professor of Theoretical Physics at Vienna Technical University in Austria. Stefan and his colleagues around the world have been pushing forward the development of a device called the ‘anti-laser’. Alex and Stefan explore whether this could be the light-cancelling device of Ahmed’s imagination. And once we've created a light-cancelling device, what do we do with it? Mary Lou Jepsen is an inventor and the founder of health tech firm Openwater. She tells Alex about how she’s using light wave manipulation to open up new possibilities for medical imaging, and even treatment. This programme includes clips from: Surrounded by Sound: Ray Dolby and the Art of Noise Reduction https://www.bbc.co.uk/programmes/m002bswq CrowdScience: Can we trap light in a box? https://www.bbc.co.uk/programmes/w3cswvwy Presenter: Alex Lathbridge Producer: Tom Bonnett Editor: Ben Motley(Photo: Eyesight and vision concept - stock photo Credit: J Studios / Getty Images)

CrowdScience listener Griffith in Ghana, isn’t JUST a CrowdScience listener. He’s also a listener to our sister show on the World Service, Unexpected Elements. But he’s noticed something funny. In the weekly Unexpected Elements multiple-choice quiz, the answer is almost NEVER ‘a’. It’s nearly always ‘b’, or ‘c’. Why is this? When we set the quiz, why are we so reluctant to choose option ‘a’? His question leads presenter Alex Lathbridge on a journey into the murky depths of our brain, where he discovers the cognitive biases which so often trip us up in games of chance, or probability. Your brain might be a marvellous machine when it comes to figuring out how to understand the world, but sometimes, in the name of efficiency, it takes clever little short-cuts to the answer. This pragmatic approach to problem solving helps us manage an incredibly complicated world. But occasionally, especially when it comes to mathematics, chance, and probability, it leads us in the wrong direction. With the help of mathematician Kit Yates from the University of Bath in the UK, and some rather stale sweets, Alex will be finding out how to win at games of chance. Alex also explores the world of gaming, and gambling. Games of chance in which our intuition sometimes lets us down, and makes us choose unwisely. Rachel Croson, Professor of Economics at the University of Minnesota, USA, talks us through how the human brain can work against us. But can knowledge of those human pitfalls help us to win? Alex hears from Maria Konnikova, who turned her research on the psychology of poker into a successful gambling career. Can we really use maths to beat our brains, and learn how to win more often?   Presenter Alex Lathbridge Producer Emily KnightEditor Ben Motley(Photo: Close up image of multiple choice question. Credit: BBC)

CrowdScience listener Namrata and presenter Chhavi Sachdev have something in common. They both get more tanned in the summer in the United States than back home in India. Namrata wants to know why she came back from her run in Boston with such a deep tan and doesn’t have the same experience in India. She’s got quite a few theories herself and wonders if it’s to do with the angle of the sun, pollution or humidity. Chhavi talks to dermatologist Neelam Vashi, who’s based in Boston, to find out how we tan and what protects us from the sun. She meets Julian Groebner at the World Radiation Centre in Switzerland who compares the data in India and the United States for CrowdScience and comes up with a surprising answer. She also talks to Indians in Mumbai who share their attitudes to tanning and what steps they take to protect themselves from the heat of the sun. Presenter Chhavi Sachdev Producer Jo Glanville Editor Ben Motley(Photo: Woman sunbathing on sun lounger by swimming pool. Credit: IndiaPix/Getty Images)

There’s something fishy going on in the Czech Republic, where CrowdScience listener Ian lives. He keeps tropical fish, and he’s noticed that when he adds new ones to his tank, they swim with others of the same breed. He wants to know how they recognise each other. Do they know what they look like, and recognise others that look the same, or is there something else going on?Presenter Anand Jagatia takes a deep breath and dives into the science. At the Blue Reef Aquarium in Portsmouth, Dr Lauren Nadler from the University of Southampton introduces us to some Blue Green Chromis fish to look for clues about how and why they form their large social groups. And we explore the smelly world of fish olfaction with Professor Culum Brown from Macquarie University in Sydney Australia. The mirror test is a classic way of trying to understand whether an animal can recognise itself or not. Professor Alex Jordan from the Max Plank institute in Konstanz, Germany explains how scientists place a visible mark on an animal, show it a mirror, and if the animal tries to rub it off, it suggests that the animal knows it’s seeing itself. A variety of apes, elephants and dolphins have passed with flying colours, but has a fish been able to take on the test? And are there really self-aware shoals drifting through our oceans? Presenter: Anand Jagatia Producer: Emily Bird Editor: Ben Motley(Photo:Familiarity of the two fish. Portrait of a Hemichromis lifalili. Macro- Credit: kozorog via Getty Images)

Is silence blood-curdling or blissful? CrowdScience listener Ziqi finds it intolerable and thinks that there’s a good reason for it – silence is so rare in nature that it could be a signal for danger. Presenter Marnie Chesterton is on a mission to test Ziqi’s theory, starting with her own tolerance for silence. She meets acoustic engineer Trevor Cox in the UK to find out whether silence is something we can measure. To do that she steps into an anechoic chamber, a place that’s designed to absorb all sound. In this most silent of silent places, what does silence actually sound like? Marnie also talks to researcher Eric Pfeifer in Germany, who is exploring the impact of spending time in silence and has evidence to suggest that it could be a positive experience. And neuroscientist Marta Moita in Portugal tells Marnie about how rats use silence to detect a threat in their environment. Her discoveries may hold the answer to Ziqi’s question. Presenter Marnie Chesterton Producer Jo Glanville Editor Ben Motley (Photo:Young woman covering ears ignoring loud noise, plugging ears with fingers annoyed by noisy neighbours - stock photo- Credit: Mariia Vitkovska via Getty Images)

Crowdscience listener Ryosuke grew up in Japan, and spent his childhood summers catching cicadas in the park. For people in Japan, the sound of their chirping signals the first true summer day. But until they emerge, these enigmatic insects live underground - often for many years. Ryosuke wants to know how they know the time is right, and CrowdScience is on the case. Presenter Anand Jagatia pieces together the story of the species, and meets the small but dedicated group of academics worldwide who’ve been able to study them. In a field near Girona, Spain, he meets a scientist who’s spent the last twenty years counting them. How will a temperature probe help us work out when they might emerge, and what are they doing underground for so many years anyway? In nearby Barcelona, another scientist cuts open the stem of a tomato plant and Anand watches as the sap flows out. Could this be a clue to how cicadas sense what’s going on above ground? And he meets a cicada breeder in the US who has discovered a link between the life cycle of cicadas and the fruiting of a peach tree. Armed with that knowledge, can you really make time move faster for tree and insect alike? Presenter: Anand Jagatia Producer: Robbie Wojciechowski Editor: Ben Motley(Photo:Cicada on Hosta Leaf - stock photo Credit: KenWiedemann via Getty Images)

CrowdScience listener Limbikani in Zambia is always being told he has his Dad’s laugh, so he set us the challenge of trying to find out whether a laugh can be passed down in our genes or if it’s something we learn from our environment. Presenter Caroline Steel steps into the world of one of the world’s greatest laughter experts, Professor Sophie Scott, neuroscientist at University College London. In her office stuffed with memorabilia of a life filled with fun, they discuss how the shape of our bodies could play a role in how we laugh. Also joining the fun is Dr Gil Greengross, evolutionary psychologist at Aberystwyth University in Wales, UK. Gil tells us how Charles Darwin was the first person to question how laughter evolved. Caroline also speaks to Dr Nancy Segal, Professor of Developmental Psychology and Director of the Twin Studies Center at California State University, Fullerton. Nancy is an expert in studies that demonstrate the role of nature vs nurture in how who we are and how we behave. She tells the story of the ‘Giggle Twins’, who were separated at birth but found they laughed identically when they met three decades later. So does that mean that we really do inherit our laughs from our parents? Presenter: Caroline Steel Producer: Tom Bonnett Editor: Ben Motley Credit: The sound of rats laughing (slowed down so that our ears can detect the ultrasound) is courtesy of Dr. Jaak Panksepp(Photo: Father and son on yellow background- stock photo Credit: Georgijevic via Getty Images)

In 2025, the crack team of intrepid presenters here on CrowdScience have been on some incredible adventures. They’ve wondered whether water is wet, and gone a hunt for a missing tangerine. They’ve wondered why animals swallow rocks, imagined what would happen if the earth spun backwards and pondered whether atoms are immortal. But, as the year draws to a close, Anand Jagatia is wondering… have they REALLY been paying attention? Time to put them to the test! In this special programme, Anand gathers the other four presenters into a studio together – Caroline, Alex, Marnie and Chhavi, for an end-of-year quiz – and you can join in at home! Presenters: Anand Jagatia, Caroline Steel, Alex Lathbridge, Marnie Chesterton and Chhavi Sachdev Producer: Emily Knight Editor: Ben Motley(Photo: CrowdScience presenters in the studio with purple background Credit: BBC)

When some people are wandering around in shorts and a t-shirt, others are wrapped up in warm coats and jumpers. How come our responses to cold weather are so different? People have been living in cold environments for thousands of years. So why do some of us struggle with the cold more than others, and what, if any, adaptations have our bodies made to cope in freezing temperatures? CrowdScience listener Anne from the UK is amazed by the warm houses of her neighbours, and wants to know whether her background might have affected her perspective on the cold. Caroline Steel investigates, visiting a laboratory in Loughborough University, UK, that pushes the body to the extreme. Dr Matt Maley explains what happens inside our systems to help us survive the plummeting thermostat and how this adaption can vary from person to person. But it’s not just biological. Our culture impacts our experience of cold too. CrowdScience heads to Norway to meet the global community on the icy Arctic island of Svalbard. There Caroline meets Associate Professor Gunhild Sætren at the Arctic Safety Centre to find out the important role appropriate clothing plays in being prepared for the chilly weather. And we speak to Dr Cara Ocobock at the University of Notre Dame, USA, who tells us about her research comparing Finnish reindeer herders and office workers reactions to cold temperatures. Presenter: Caroline Steel Producer: Hannah Fisher Editor: Ben Motley(Photo: Woman enjoying winter playing in fresh snow. Credit: Olga Pankova/Getty Images)