When a new cause is introduced into science, as often as not it is accepted without trouble. Few, if any, had worries about the Watson–Crick double helix and the subsequent working out of the genetic code. Genetics was put on a molecular causal basis. However, it is not uncommon for there to be opposition. Huygens’ wave theory of light was an outsider for nearly two centuries. Sometimes worries are ongoing. One doubts that, as long as there are those interested in mental health, Freud’s Oedipus Complex is going to be happily accepted by all. There have been, continue to be, and probably always will be disputes, often bitter, about its causal status. As we have seen, natural selection did not have an altogether easy birth. But as time went by, things seem to have improved. Newton and Leibniz all over again.