Last week, public health officials declared a ‘national incident’ after they found vaccine-derived poliovirus in London sewage samples. No cases of polio symptoms have been reported but there is evidence the virus is spreading. So what does it mean to have found the virus almost 20 years after the UK was declared polio-free? Ian Sample speaks to epidemiologist Nicholas Grassly to find out how worried we should be and what it means for the global effort to eradicate polio.. Help support our independent journalism at theguardian.com/sciencepod

When the Guardian’s UK technology editor Alex Hern was contacted on Twitter to ask if he was involved in a new cryptocurrency called Tsuka, he assumed they just wanted him to buy it. He ignored the messages. But soon after Alex realised that, without knowing it, he was already involved. What happened next reveals a lot about the strange world of ‘shitcoins’ – cryptocurrencies with no reason for existence beyond buying low and selling high. Madeleine Finlay speaks to Alex Hern about his shitcoin saga, and how the lines can get blurred between a gamble and a scam. Help support our independent journalism at theguardian.com/sciencepod

After wolves were reintroduced to Yellowstone national park in 1995, researchers noticed some big ecological changes, leading to the regeneration of the landscape. It’s an argument used to justify the return of apex predators – but it’s increasingly being challenged. Phoebe Weston talks to Ian Sample about whether wolves really have the power to shape ecosystems, and what that means for the debate about bringing them back to the UK. Help support our independent journalism at theguardian.com/sciencepod

They support an incredible array of biodiversity and may also be some of the world’s most effective carbon sinks. But vast swathes of seagrass meadows have been lost in the last century, and they continue to vanish at the rate of a football pitch every half hour. Madeleine Finlay makes a trip out of the Guardian office to visit a rewilding project in Hampshire. She speaks to marine biologist Tim Ferrero about the challenges of replanting seagrass meadows and what hope it offers.. Help support our independent journalism at theguardian.com/sciencepod

Last week an engineer at Google claimed that an AI chatbot he worked with, known as LaMDA, had become ‘sentient’. Blake Lemoine published a transcript of his conversations with LaMDA that included responses about having feelings and fearing death. But could it really be conscious? AI researcher and author Kate Crawford speaks to Ian Sample about how LaMDA actually works, and why we shouldn’t worry about the inner life of software – for now.. Help support our independent journalism at theguardian.com/sciencepod