Are such laws as that against eating blood (Gen 9:4) and murder (9:5-6) the first legislation in the world? Was there no human law before this?

On the one hand, God had set rules and requirements for man previously; insofar as any command of God constitutes law, then there was law before this. Moreover, there was something like human law in the form of Lamech’s bold and shameless declaration, “If Cain is avenged sevenfold, Then Lamech seventy-sevenfold” (4:24). Some commentators portray this as a kind of law; if Lamech could back up his boast, as he probably could, then it could have been something like a (deviant, unjust) law. But on the other hand, the laws set forth here are indeed the first divinely-promulgated law which was nonetheless to be enforced by man. In this regard, it is the original of the sorts of laws given to Moses.