Élie Metchnikoff
In his preface to the play, Čapek noted the inspiration for the play of a scientific idea by Élie Metchnikoff, namely that aging results from a process of cellular autointoxication. Čapek also commented on the coincidence that his play appeared at around the same time as George Bernard Shaw's play "Back to Methuselah", which dealt with the similar theme of extended human life span, but with a very different conclusion. Čapek also attempted to qualify criticism of his philosophical point of view, with respect to the idea of extended human life span, as pessimistic.