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.

1. Correction, Noah was to collect seven of each clean beast, and two of those that were unclean.
2. The classification of animals into two categories - clean and unclean, existed as early as Noah.
3. The proportion of clean males to clean females for each species is not specified, but I suspect there were only one or two males and the rest females.
4. God has probably given dietary advice from the beginning.