Crocodiles have been the same for millennia upon millennia. What's going on? Why are they so uneventful in terms of evolution? Plus, we ask why we have different blood types. Like this podcast? Please help us by <a href="https://www.thenakedscientists.com/donate">supporting the Naked Scientists</a>

Why do we have different blood groups?

Each week we set out to solve one of the world's weirdest, wackiest, funniest and funkiest scientific puzzles. And along with the answer there's a brand new question to think about for next time...