As written by Esther Lederberg: "At this same time, L. Cavalli in Milan Italy, discovered the phenomenon of sterility from a different angle. Exchange of data showed that if I had done an experiment, he had planned to do it, but had completed another that we had planned. So we decided to pool forces and collaborate." See http://www.estherMlederberg.com/Clark_MemorialVita/HISTORY52.html