Gen 7:1 And the LORD said unto Noah, Come thou and all thy house into the ark; for thee have I seen righteous before me in this generation. 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. 3 Of fowls also of the air by sevens, the male and the female; to keep seed alive upon the face of all the earth.
Most people believe that God brought the animals two by two into the ark. That is only partially true. The "clean" animals were to be brought in by sevens, four males and three females. The reasons for this are two-fold.
First, it insured that plenty of clean animals would be available for use. There would be 3 pairs of clean animals for every 1 pair of unclean.
But the reason for the remaining male animal was that it was reserved for sacrifice once they exited the ark.
I suppose we could also make a case for the seven animals being that this is God's number of completion. By the way, there were 8 human souls on board, God's number of grace and renewal.
So, there you have it. God's Word once again messes up a number of pithy little songs and beliefs.