What made the first person who brought a Korban (Kayin and Hevel in Ber. 3:3-5 or Adam in Avodah Zara 8a) think that G-d would approve of a person killing one of his creatures and presenting it to Him (G-d) as a gift? The generations before Noach were not allowed eat meat. What made them think they could kill animals for a korban? Similarly for Noach to bring 5 pairs of kosher animals as a korban when the world needed to be repopulated seems strange to me. Obviously their intuition was correct, but I can’t understand the basis for that intuition.
Someone said that G-d commanded a Korban from Adam, but didn’t give a source.
Adam Harishon was a navi, and he spoke to H-shem. He also had a tremendous intuition, as the verse says that he called each animal according to it’s nature just by looking at it. The Midrash Hagadol (Bereishis 4-3) says that Adam told his children on the eve of the 15th of Nissan that the Jews eventually are going to bring the Korban Pesach, therefore they should also bring a korban. Obviously he knew this with the power of nevuah or ruach hakodesh. Aside from this H-shem only told Adam that the animal were not his to eat, bringing the animal is in order to service H-shem, and not for Adam’s personal enjoyment. As a side point, was Adam allowed to kill an animal for its skin? I would assume that he was, because the posuk says “umilu es ha’aetz v’kivshuha”, that he was given permission to conquer the world, including the animals.
Regarding the fact that Noach brought five out of the seven surviving animals as a korban, it is not strange at all. This was the original reason why these animals were brought into the ark in the first place. Al other animal only had two animals representing that species, and only the kosher ones had more than two. See Rashi on that verse.