Rather than simply eating until we are full, humans selectively try to eat the right amounts of three macronutrients – protein, carbs and fat – plus two micronutrients, sodium and calcium. It turns out we have five separate appetites that drive us to eat the right amount of each.In the pod this week are New Scientist journalists Rowan Hooper, Penny Sarchet, and Graham Lawton. They discuss an evolutionary explanation for the obesity epidemic: the fact humans will gorge on carbohydrates to try and get enough protein if they find themselves deprived of this nutrient.The team also discuss an implant that lets blind people ‘see’ letters traced on their brain’s surface, they analyse how the coronavirus is impacting conservation efforts around the world, and they delve into mud on Mars. If what we thought was lava pouring out of Martian volcanoes is actually mud, it has implications for life on the planet - which leads to a message from Elon Musk. To find out more, subscribe at newscientist.com/podcasts. Our GDPR privacy policy was updated on August 8, 2022. Visit acast.com/privacy for more information.