The human race, which is now funnelled through the three sons of Noah, must repopulate the earth, and there is a special promise for its preservation. Animals were now ferocious and wild again.
The power granted to Noah and his descendants over animal life applies to other uses besides food. He may use their bodies for clothing; he may use them to investigate the effects of drugs or illness so as to derive understanding of how man can be benefited. Of course the benefit to man must be real, and not just to satisfy his greed or other evil appetites. But especially it is food that Moses refers to, for even before the flood man had the right to take life for the purpose of clothing and sacrifice. Though the earth is made for man, we can take nothing except by the permission of God and he sets limits on what we may do.
If God now granted man the right to eat the flesh of any animal he pleased, why under the law were there restrictions added that forbade him to eat certain meats? These restrictions were added to teach the Jews about the distinction between clean and unclean, but those lessons were only temporary since the real distinction between clean and unclean exists in the spiritual realm not the physical. The New Testament later ended these Mosaic food laws and returned to the original rule given to Noah (Mark 7:19; Romans 14:14).