At a recent ceremony for world leaders in Beijing, a hot mic picked up a surprising exchange between Vladimir Putin and Xi Jinping about the possibility of living to 150. Putin suggested the secret might lie in repeated organ transplants. But is this the new frontier of anti-ageing research or a fringe and unproven theory? To find out, science editor Ian Sample speaks to Russian affairs reporter Pjotr Sauer and to John S Tregoning, professor of vaccine immunology at Imperial College London and author of Live Forever: A Curious Scientist’s Guide to Wellness, Ageing and Death. Help support our independent journalism at theguardian.com/sciencepod

The fertility rate in England and Wales has fallen for the third year in a row – a trend mirrored across the world, with two-thirds of the global population now living in countries with below-replacement-level fertility. In the second episode of a two-part series, Madeleine Finlay speaks to Dean Spears, assistant professor of economics at the University of Texas at Austin, and Dr Jennifer Sciubba, chief executive of the Population Reference Bureau, to ask whether declining birth rates are really something to worry about – and how societies can adapt to a future with fewer children. Watch the new Guardian documentary Between Moon Tides. Help support our independent journalism at theguardian.com/sciencepod

The fertility rate in England and Wales has fallen for the third year in a row. It is a story that is being repeated all over the world, with two thirds of the global population now living in countries with below replacement level fertility. Low fertility rates have become a talking point on the political right, with Elon Musk claiming that population decline is an existential threat to the future of humanity. But for others, the timescales involved are too vast to start worrying about now. So how should we be thinking about population decline? In episode one of a two-part series, Madeleine Finlay speaks to Dean Spears, assistant professor of economics at the University of Texas at Austin, and to Dr Jennifer Sciubba, president and CEO of the Population Reference Bureau, to find out what has happened to global birth rates, and how governments are trying to tackle the fall. Help support our independent journalism at theguardian.com/sciencepod

Psychologists have traditionally believed we become less curious as we age, but recent research has shown that curiosity actually becomes more targeted and specific in our later years. To find out why this happens, and how maintaining broad curiosity into older age can help keep our brains young, Madeleine Finlay hears from Dr Mary Whatley, an assistant professor of psychology at Western Carolina University, and Dr Matthias Gruber, of Cardiff University’s Brain Imaging Centre. Help support our independent journalism at theguardian.com/sciencepod

It’s been a dramatic week at the US Centres for Disease Control and Prevention (CDC). In the space of seven days, the agency’s head was sacked and replaced by an interim head, four senior staff members resigned, and existing staff took to the streets to express support for their ousted leaders. To understand how everything unfolded and what it could mean for the health of Americans, science editor Ian Sample hears from health reporter Melody Schreiber and former CDC director Mandy Cohen. Help support our independent journalism at theguardian.com/sciencepod

There are increasing reports of people experiencing delusions after intensive use of AI chatbots. The phenomenon, dubbed ‘AI psychosis’, has raised concerns that features built into large language models may contribute to some users losing touch with reality. Madeleine Finlay speaks to Dr Hamilton Morrin, a psychiatrist and researcher at King’s College London, about his recent preprint exploring who is at risk and how models could be made safer. Help support our independent journalism at theguardian.com/sciencepod

For more than a decade, scientists have been puzzling over what was causing billions of starfish to dissolve into piles of white goo. Sea star wasting disease has ravaged starfish populations, wiping out 90% of the once common sunflower sea star. Now, researchers have finally identified the culprit. Madeleine Finlay speaks to Dr Melanie Prentice, one of the team to crack the case. She explains the impact the disease has had on the marine environment, how they found the pathogen responsible, and what it means for sea stars’ recovery. Help support our independent journalism at theguardian.com/sciencepod

Scientists have found the first robust evidence that people’s genes affect their chances of developing myalgic encephalomyelitis or chronic fatigue syndrome (ME/CFS), a mysterious and debilitating illness that has been neglected and dismissed for decades by many in the medical community. To find out more, Madeleine Finlay speaks to science editor Ian Sample and to Nicky Proctor, who has ME and took part in the research. She also hears from Beth Pollack, a research scientist at the Massachusetts Institute of Technology who studies ME/CFS and related conditions, about how scientific understanding of the illness has improved and how scientists are transforming this knowledge into ideas about future treatments. Help support our independent journalism at theguardian.com/sciencepod

After three years of negotiating, talks over a global plastics treaty came to an end in Geneva last week with no agreement in place. So why has it been so difficult to get countries to agree to cut plastic production? Madeleine Finlay hears from Karen McVeigh, a senior reporter for Guardian Seascapes, about a particularly damaging form of plastic pollution causing devastation off the coast of Kerala, and where we go now that countries have failed to reach a deal. Help support our independent journalism at theguardian.com/sciencepod

Europe is suffering from another heatwave as deadly temperatures of up to 44C hit the continent and wildfires blazed across the Mediterranean. To find out why Europe is heating faster than anywhere else, Madeleine Finlay speaks to the Guardian’s Europe environment correspondent, Ajit Niranjan, and to Adam Taylor, professor of anatomy at Lancaster University, to find out how we can try to stay cool as the temperature rises. Help support our independent journalism at theguardian.com/sciencepod