The challenge of simultaneous invention
Have you ever arrived at a party or work to find that someone is wearing the same shirt, pants, or shoes as you? It's a curiosity of modern life that we convince ourselves our wardrobes are unique, despite selecting the items from department stores' racks filled with dozens of the same shirts, slacks, and blouses. An observant shopper watching the goings on at the mall can easily imagine someone—roughly her size—heading home with a similar outfit. Yet if she ever does meet her fashion doppelganger at a party or on the street, she is astonished: "How could she wear my wardrobe?" Once obtained, regardless of how or why, we take conceptual possession: "That shirt with those pants is my idea."
Fashion is a good metaphor for the problem of simultaneous inventorship: the situation when two or more people claim to have invented something. Like wardrobe collision, it seems improbable in the moment that two people could unintentionally invent the same thing around the same time; stepping back, it's easy to see why it happens. The invention of calculus, television, telephones, bicycles, motion pictures, MRI imaging, and automobiles all involve various kinds of simultaneous, overlapping, or disputed origins.
It's common because innovations demand prerequisite knowledge—inventing a new cocktail (e.g., The Berkun  ) requires experience with different liquors, and creating a new dance step (e.g., The Edison) demands knowledge of choreography. This narrows ...