Before the flood all mankind was descendant from one man – Adam. Human beings became corrupt and Hashem destroyed all in the universe except for Noach and his descendants. After the flood all mankind descended from Noach who himself was a progeny of Adam. (Of course, so was his wife.)
In both cases Hashem gave instructions and a blessing to the one who was to become the father of all generations. There is one difference. Noach and his offspring were permitted to use the animals and to eat their flesh, something that was prohibited to man before the flood.
Obviously it was because the animals survived through the help of Noach that this concession was granted. However, many of the Torah commentaries read another meaning into this permission. It was to distinguish between humankind and the animal kingdom. Man stands on a higher plane than animals. He has greater distinctive abilities and through his power of reasoning and understanding he can reach gigantic intellectual heights.
These abilities make it obligatory for man to demonstrate greater civil behavior. He cannot prey on other humans and act as animals act towards each other. He must use his intelligence to create a better life for himself and others. War and corruption are not the proper course to follow for they lead to the same vice and evil that brought about the flood in the first place. Then it was the flood. Today it can be a nuclear conflagration. Mankind has to learn how to live peacefully with each other. That was the intention of the Creator.