Musar zu Bereschit 5:1

Bereshit Rabbah 24,6 comments on Genesis 5,1 זה ספר תולדת אדם, "This is the book of the descendants of man," that those mentioned now are descendants, whereas the previous ones were not descendants. What then were the earlier ones? Were they deities perhaps? [sarcastically] The answer given is that the generations אדם-שת-אנוש were indeed תולדות. [The Midrash goes on to elaborate on all the changes that took place on earth during Enosh's lifetime, indicating a radical decline in man's spirituality. Ed]