The Luriaâ `` DelbrÃ 1\/4 ck experiment , 1943 , asks the question : are mutations independent of natural selection ? Or are they directed by the selection ? The Luriaâ `` DelbrÃ 1\/4 ck experiment ( 1943 ) ( also called the Fluctuation Test ) demonstrates that in bacteria , genetic mutations arise in the absence of selection , rather than being a response to selection .