[For my Natural Law and Scriptural Authority Davenant Hall class, every other week I must write a reflection on a biblical text as it pertains to the themes of the course. This is my first of these, on Genesis 6 & 11.]
Genesis 6 makes for a very peculiar case when considering natural law and the natural order more generally inasmuch as it represents a breakdown of that order. Not that God's providence or creative work failed, but the human administration went so badly awry that God's providence and creative work themselves had to take a frightful turn. A couple aspects of the buildup to the Flood stand out from this perspective.
For one, we see an affirmation of the widely recognized principle of a certain kind of equitable retributive justice. "An eye for an eye," taught in revelation, is also clearly taught in nature, as the multitudes of unbelievers who have used similar principles demonstrates. At this time, the world was recently created, but human violence worked to extinguish what God has wrought. As the violence grew more severe, they even joined together with the opponents of God in creation, who also seek to deface and unmake His work. The just and equitable response which God employs is in keeping with the offense: those who have wiped the innocent from God's world are themselves wiped from God's world, and the earth which they have polluted by blood is cleaned by water. This kind of proportion between crime and punishment is a common principle which almost all humans know, and God Himself works by it. This correspondence between common human moral knowledge and God's own character does support the notion of a law intrinsic to human nature which reflects the eternal law by which God Himself operates and according to which God ordered human nature.
This text also highlights a common observation about the natural order: the interconnectedness of the natures involved. Human nature is not constituted solely with refernece to itself, but also in relation to God and, most relevant to this account, the rest of creation, particularly on earth. Humans stand at the helm of creation, and as go we, so goes the earth. This fact reveals itself even apart from revelation as soon as children notice the disproportionate power humans have over their surroundings when compared to all other creatures. Man tames animals, cultivates crops, crafts with stone, and channels waters. Yet he is also dependent upon the peculiar natural ordering of each of these lower creatures. When he abuses his own position, the rest of the world beneath him suffers. Perhaps modern people could be uniquely suited to grasp this as we see the effects of industrialization and the modern consumer economy on animals, plants, and the face of the earth itself. It is probably noteworthy that the text first highlights the wickedness of men and angels, but then it does move to say that "the earth was corrupt" and that "all flesh," which in context seems to include animals, had corrupted its ways. So the whole creation had to be washed. We should always expect, then, to find in our observations of the natural order ways in which our divinely given responsibility as God's image-bearers affects and is affected by all other parts of this world, so that we and the rest of creation can share both in corruption and in blessedness.
Genesis 11 and the Tower of Babel account make one minor point clear at the outset. Despite the intense corruptions of sin and the catastrophe of the Flood, human nature is still intact in some meaningful sense. The people can still think, speak, create, reason, etc. This also means the natural law continues in effect. Here a possible question arises. It does seem that the desire the people of Babel had for unity and common culture was a natural and perhaps evidently good one in itself. Does not nature show the benefits of a family with solidarity, of a society united in common labor, etc? By contrast, the idea to fill the earth and subdue it, which had to be disregarded or at least put on hold for the Babel project, originates from a divine command. It might seem to us, but probably did seem to the people at the time, also a very unnatural one. In the early days of the human race after the Flood, the virtue of unity probably seemed obvious, both because of the limits of what people could accomplish on their own post-apocalypse and because unity seems naturally to be a remedy to the kind of unrestrained violence that had triggered the Flood to begin with. The divine command to spread out and do a variety of kinds of work seems strange given the clearly naturally discernable benefits of a united people.
This slight tension evaporates, though, on considering the role of divine commands as often making explicit what might be difficult to deduce from nature despite its hypothetical knowability. The benefits of having many peoples in different parts of the world working in different ways to subdue and tend different regions is almost obvious to modern people in a way it probably was not in the time of Babel. We can discern that, in the long run, the people were better off moving on and diversifying into a more variegated humanity than they would have been if they had all stayed in Babel doing one thing in one language. But since this might have been much less obvious at the time, a divine command was (or rather ought to have been) a perfect substitute and assurance for the naturally discernable wisdom of diversifying.
Two final notes: the decreasing lifespans after the Flood seem to highlight just how detrimental sin is. Fighting against the requirements of God's natural law is fighting against humanity's own created nature and is thus necessarily self-destructive. Also, the introduction of Sarai as the first mentioned barren woman will probably be relevant to reflections in later chapters.