The same theory of flight that birds use to fly, i.e., none. Some birds might notice they use less energy if they don't flap their wings and instead catch an up

The same theory of flight that birds use to fly, i.e., none. Some birds might notice they use less energy if they don't flap their wings and instead catch an updraft. I don't think they need a theory of pressure gradients to exploit this phenomenon. They just have to feel it in their bones. I know my response is glib, but no "theory of" is needed to do useful work. Humans can build intuitive understanding through personal experience, observation, and thinking. And they can pass some forms of this understanding via apprenticeship, laws, rules, organizational structures and cultural norms among other things.