Despite their diminutive scale, peanuts play an outsized role in American culture. Peanut butter has long been a mainstay of the American lunch box, with its sticky, slightly sweet nuttiness flavoring the memories of generation after generation of kids. And it’s hard to imagine ball games without, as the song goes, peanuts and Cracker Jacks (which, of course, also contain peanuts). But today, peanuts are the source of both hope and fear: While there’s been a surprisingly steep rise of peanut allergies in recent decades that can—though rarely—lead to death, peanut butter is also the basis of a medical therapy used to save the lives of millions of children around the world. This episode, we discover how the humble peanut got to be such a big deal.

Though we call it a nut, the peanut is actually a legume, more closely related to soybeans and lentils than almonds and walnuts. It’s also a botanical anomaly: the plant produces a beautiful yellow orchid-like flower, but then pushes out a peg that grows downward into the ground underneath, where it forms into a peanut. This flower-above-ground-then-burrow-underground-to-fruit trick is replicated by only one other plant in the world, the bambara groundnut, native to West Africa.