Scholars teach us that the book of Genesis splices two different flood stories into one. For example, the first author states two of each kind of animal enters the ark, making no distinction between clean and unclean:
Genesis 6:19 And of every living thing of all flesh, two of every sort shalt thou bring into the ark, to keep them alive with thee; they shall be male and female.
The second author states that seven pairs of clean animals enter the ark:
Genesis 7:2 Of every clean beast thou shalt take to thee by sevens, the male and his female: and of beasts that are not clean by two, the male and his female.