Form criticism began in the early twentieth century when theologian Karl Ludwig Schmidt observed that Mark's Gospel is composed of short units. Schmidt asserted these small units were remnants and evidence of the oral tradition that preceded the writing of the gospels. Bible scholar Richard Bauckham says this "most significant insight," which established the foundation of form criticism, has never been refuted. Hermann Gunkel (1862–1932) and Martin Dibelius (1883–1947) built from this insight and pioneered form criticism. By the 1950s and 1960s, Rudolf Bultmann and form criticism were the "center of the theological conversation in both Europe and North America".