Yesterday, I was giving lectures at University of Osaka.
Walking along the street, I saw two common bluebottle (Graphium sarpedon) butterflies in the sky. They kept flying, chasing each other.
After a while, one of them began circling around the other. The movement was quite rapid. The circle was completed more than once a second, approximately.
I was fascinated by this elegant and dynamic display of behavior. It must be written in the genetic code. Generations after generations have performed this aerial dance without knowing how or why.