As Noah and his family were the only ones not to have a share in the corruptness of the age, so the animals received into the ark were such as had led a natural life. For the animals of the time were as immoral as the men: the dog united with the wolf, the cock with the pea-fowl, and many others paid no heed to sexual purity. Those that were saved were such as had kept themselves untainted.
Before the flood the number of unclean animals had been greater than the number of the clean. Afterward the ratio was reversed, because while seven pairs of clean animals were preserved in the ark, but two pairs of the unclean were preserved.