Scholars from the 1970s and into the 1990s, produced an "explosion of studies" on structure, genre, text-type, setting and language that challenged several of form criticism's aspects and assumptions. For example, the period of the twentieth century dominated by form criticism is marked by Bultmann's extreme skepticism concerning what can be known about the historical Jesus and his sayings. Some form critics assumed these same skeptical presuppositions based largely on their understanding of oral transmission and folklore. During the latter half of the twentieth century, field studies of cultures with existing oral traditions directly impacted many of these presuppositions. In 1978, research by linguists Milman Parry and Albert Bates Lord was used to undermine Gunkel's belief that "short narratives evolved into longer cycles". Within these oral cultures, literacy did not replace memory in a natural evolution. Instead, writing was used to enhance memory in an overlap of written and oral tradition. Susan Niditch concluded from her orality studies that: "no longer are many scholars convinced ... that the most seemingly oral-traditional or formulaic pieces are earliest in date". In this manner, compelling evidence developed against the form critical belief that Jesus's sayings were formed by Christian communities. As John Niles indicates, the "older idea of 'an ideal folk community—an undifferentiated company of rustics, each of whom contributes equally to the process of oral tradition,' is no longer tenable". According to Eddy and Boyd, these various conclusions directly undermine assumptions about "Sitz im leben:" "In light of what we now know of oral traditions, no necessary correlation between literary forms and "life situations" im leben can be confidently drawn".