Why don't more animals have opposable thumbs?

On a recent kayaking trip, CrowdScience listener Lanier sliced through his right thumb, putting it out of action for a while. This made life difficult, as he couldn’t button his shirt, tie his shoelaces or type efficiently on his smartphone. Missing the use of his thumb made him wonder: since opposable thumbs are so advantageous to those of us who have them, why didn’t they evolve in more species?

Host Marnie Chesterton unpicks the evolution of our own unique thumbs with the help of paleoanthropologist Tracy Kivell, learning how our grip compares to that of othe...