Although it began as a political documentary, the series has become a film of human nature and existentialism. In the director's commentary for "42 Up", Apted comments that he did not realise the series had changed tone from political to personal until "21 Up", when he showed the film to American friends who encouraged him to submit it (successfully) to American film festivals. Apted also comments that this realisation was a relief to him and allowed the films to breathe a little more.