Are wild mammals only 4% of the mammal population?

A widely respected and cited study says humans and livestock account for 96% of all mammals on Earth. We ask how the study was carried out and what hope there might be for the future. Plus we answer another listener question about whether most mammals are in fact rodents. With the help of Dr Hannah Ritchie, Deputy Editor at Our World in Data and Dr Axel Rossberg, Reader in Theoretical Ecology at Queen Mary University of London.