People around the world are living longer and, on the whole, having fewer children. What does this mean for future populations? Sarah Harper CBE, Professor in Gerontology at the University of Oxford, tells presenter Jim Al-Khalili how it could affect pensions, why it might mean we work for longer, and discusses the ways modern life is changing global attitudes to when we have children, and whether we have them at all. Fertility and ageing have been Sarah's life's work and she tells her story of giving up a career in the media to carry out in-depth research, and going on to study population change in the UK and China, setting up the Oxford Institute of Population Ageing and later becoming a Scientific Advisor to UK Government.

Presenter: Jim Al-Khalili

Our primate cousins fascinate us, with their uncanny similarities to us. Studying other apes and monkeys also helps us figure out the evolutionary puzzle of what makes us uniquely human. Sarah Blaffer Hrdy’s work brings a female perspective to this puzzle, correcting sexist stereotypes like the aggressive, philandering male and the coy, passive female.

Sarah is professor emerita of anthropology at the University of California, Davis, and studies female primate behaviour to create a richer picture of our evolutionary history, as well as what it means to be a woman or a parent today. Her overarching aim is to understand the human condition, a goal she initially planned to pursue by writing novels. Instead, she found her way into science: her ground-breaking study of infanticide among langur monkeys in northern India overturned assumptions about these monkeys’ murderous motivations. Later in her career, she looked into reproductive and parenting strategies across species. We humans are primed by evolution, she believes, to need a lot of support raising our children. And that is a concern she found reflected in her own life, juggling family commitments with her career ambitions as a field researcher, teacher, and science writer.

The Life Scientific returns with a special episode from the USA; Princeton, New Jersey, to be precise. Here, the Institute for Advanced Study has hosted some of the greatest scientific minds of our time - Einstein was one of its first professors, J. Robert Oppenheimer its longest-serving director - and today's guest counts among them. Edward Witten is professor emeritus at the institute and the physicist behind M-Theory, a leading contender for what is commonly referred to as ‘the theory of everything’, uniting quantum mechanics and Einstein’s theory of gravity. He talks to Jim al-Khalili about a career that’s spanned some of the most exciting periods in modern theoretical physics - and about one particular problem that has obsessed and eluded him since his days as a student.

Producer: Lucy Taylor

Exercise in older age is high on the agenda, but the idea that with age comes bags of time and a desire to ‘get out there’ isn’t true for a lot of us. How do you juggle exercise around caring for partners, grandchildren or staying in work? What if you haven’t exercised for years? What can your body take, and how has it changed with age? James Gallagher hears how octogenarian athlete ‘Irongran’ keeps going, he explores the mental and physical barriers that stop us exercising and he finds out what he might feel like in 40 years as he pulls on an ageing suit.

(Photo: Elderly man going for a run. Credit: Charday Penn / Getty Images)

How many hours do you spend sitting down per day? Six? Maybe eight? Or 10? Between commuting, working and relaxing, sitting can soon add up to hours and hours. James Gallagher delves into the science to find out exactly how much sitting is too much; when does it become worrying for our health? James visits a lab to explore what prolonged sitting does to the body and he’ll find out whether there’s anything you can do to offset the effects of sitting a lot. We’ll hear about the origins of sitting research - and just because we like to explore every angle on a topic, we’ll hear all about why standing too much can also be a worry.

(Photo: Woman sitting at desk in office. Credit: Richard Drury / Getty Images)

A look at the evidence that links the health of our mouths with the rest of our bodies.

Adam Hart investigates the fastest land animal in the world – the cheetah! Built for high-speed chases, these spotted cats are slender, with semi-retractable claws for good grip and a flexible spine plus a long tail for balance and manoeuvrability. Cheetahs rely on speed over brute strength when hunting – and can make tight, quick turns to shift course in fast pursuit of their prey. But with shrinking populations cheetahs are classified as vulnerable – so what’s being done in terms of conservation and are these projects having any success?

Adam hears how cheetahs differ from lions and leopards and learns about their relationships with other predators. He looks at their unique adaptions and behaviours, as well as the different approaches that conservationists are undertaking to try and reverse the population decline. And we also hear about the re-introduction of cheetahs to India.

Contributors:

Professor Sarah Durant is from the Zoological Society of London and is project leader of the Africa Range-Wide Cheetah Conservation Initiative.

Vincent van der Merwe is director of The Metapopulation Initiative and is cheetah metapopulation coordinator for Southern Africa and India.

Presenter: Professor Adam Hart

(Photo: Cheetah, Credit: Paul & Paveena Mckenzie via Getty Images)

Adam Hart investigates a frenzied and voracious fish from South America – the piranha! Said to be able to strip their prey to the bone in mere minutes, there are plenty of gruesome tales about the bubbling bloodbaths that occur when shoals of these hardy fish feed in the freshwaters across South America - from up in Venezuela in the Orinoco River, to the Amazon and down to the Paraná River in Argentina. What role did former United States President Theodore Roosevelt have in creating the piranha’s fearsome reputation? And is this reputation misguided?

Adam hears what piranhas are really like, both in the wild and in captivity. He learns about how these fish hunt, the impact that humans are having on them and tries to establish if they really are as bloodthirsty as we’ve been led to believe.

Contributors:

Marcelo Ândrade is a professor at the Federal University of Maranhão in Brazil. He researches the environments that piranha live in and their behaviour, as well as plastic ingestion by piranhas.

Hannah Thomas is the aquarium team manager at Chester Zoo in the UK where they care for 40 red-bellied piranhas.

Presenter: Professor Adam Hart

(Photo: Red-Bellied Piranha, Credit: Ed Reschke via Getty Images)

Adam Hart investigates the most famous and feared predator in all the ocean – the great white shark! With rows of large, serrated teeth, it’s often thought of as a ferocious man-eater and was the villain of the film Jaws – which frightened a generation of beachgoers. This star of the silver screen may be the subject of fascination and fright for many, but is it really the ultimate predator of the ocean as Hollywood has led us to believe?

Adam hears what it’s like to see these sharks up-close and in person for the very first time. He learns more about how great whites detect and hunt their prey, as well as the challenges they’ve been facing due to another ocean predator.

Dr Alison Towner is a postdoctoral researcher at Rhodes University in South Africa. She has a PhD in white shark ecology and has been studying the displacement of great whites due to orcas (killer whales) in South Africa.

Professor Gavin Naylor is Director of the Florida Program for Shark Research. He is a biologist who has specialised in evolutionary and population genetics, focusing on sharks.

Presenter: Professor Adam Hart

Adam Hart investigates the largest terrestrial member of the weasel family – the wolverine. They’re far more than just a superhero played by Hugh Jackman! With a reputation for gluttony and ferocity, these solitary killers use snowstorms to hunt much larger prey. Found in the snowy tundra and boreal forests of the Northern Hemisphere, their future looks uncertain – they've come into conflict with Scandinavian farmers by hunting their reindeer and are threatened by climate change in North America and Mongolia. But have we misunderstood wolverines? And can we learn to co-exist with them?

Contributors:

Rebecca Watters is founder and director of the Mongolian Wolverine Project, as well as the executive director of the Wolverine Foundation, a non-profit that’s dedicated to advancing science-based conservation of wolverines.

Jenny Mattisson is a researcher at the Norwegian Institute for Nature Research, who is involved in the monitoring of wolverines in Scandinavia. She has studied interactions between wolverines and Eurasian lynx, as well as their predation of reindeer.

Presenter: Professor Adam Hart