Law by nature is a phrase that I personally describe as something we know or should know as fact, wrong or right without any verbal or written instructions. This doesn't mean it is a binding law because not all "laws" should bind us. Daniel broke a law that sent him to the Lion's Den. We don't have to believe nature but we just know it to be true. Adam and Eve knew they were naked without being told and they quickly covered up themselves (Genesis 3:7-10). Creation proves to us that there is a designer simply by looking at it without being told (Psalm 19:1-6). The "golden rule" was not something out of thin air. It is a result of a fact that already exist within us humans. Humans generally want good things, prefer good treatment from others, love our own bodies and care for it. This is why Jesus said to do unto others what you want done to you (Luke 6:31).
Law of nature, natural law, human conscience or as I call it, Law by Nature. Whatever you choose to call it is up to you but I'm just here to say that there is indeed something of such that exists, and I'll explain. We technically don't have any book or manual called "law by nature" because it is not verbal or written. God doesn't have a separate law outside of Christ that He's going to base His judgement on. What we need for salvation has already been revealed. So, not every verbal or written law that we do have today pertains to life and godliness (2 Peter 1:3).
A conscience was born when Adam said he is hiding because he was naked. God asked WHO. Who told you Adam? WHO told you that you are naked? - Genesis 3:11. This question is key for a topic like this because that knowledge of the difference between good and evil was not verbally given to Adam from God. The instruction was to stay away from that tree - don't eat. Even though God already knew the answer to this question of who, He wanted Adam to admit that he now knows the difference between good and evil. This knowledge came from eating the fruit from that tree. God Himself said that man now KNOWS the difference between good and evil after eating from the tree that gave such knowledge (Genesis 3:22). They were "kicked" out to prevent them from eating from the second tree, which was the tree of life.
No one is saying that the Patriarchs did not receive verbal instructions from God prior to the laws that came through Moses. But Adam had zero earthly father to receive such instruction from so the only verbal law he had was directly from God. If there was a "verbal nakedness law" to Adam from God we would have known about it. Walking around naked in the garden would have been his first sin. That law would probably say something like "don't walk around naked in this garden." Adam and Eve were both naked before and after eating the fruit. The difference is that they only saw something wrong with walking around naked after they ate the fruit; not before. This natural knowledge kicked in after eating that fruit without any prior written or verbal law.
In Genesis 2:25, Adam and Eve were both naked and not ashamed. Some people say they were not ashamed because they were husband and wife. This answer is incomplete because this was not the primary reason for the lack of shame. The lack of shame they felt was from the lack of knowledge. When they gained knowledge from eating the forbidden fruit, this became the very first time that Adam and Eve knew, without being told, that it wasn't OK to be walking around naked in the garden. Not only did they make a covering for themselves from leaves but God even help make them a better covering before sending them out of the garden. When babies are born, they have no shame of nakedness because they also have no knowledge of good and evil. They are pure and sinless just like Adam was before that knowledge and sin kicked in.
Adam and Eve's sin of eating the forbidden fruit brought them shame through knowledge. That natural awareness is the reason we all are not walking around naked on the streets today. It's not primarily because some constitution said it is wrong, rather it came natural to Adam to seek some form of covering in a "public" place. Public nudity may be against some laws on paper in this day and age but there was no verbal or written rule that we know of with Adam and Eve. Yet, this was considered wrong by Adam right after the first sin and without being told.
In Genesis 2:25, Adam and Eve were both naked and not ashamed. Some people say they were not ashamed because they were husband and wife. This answer is incomplete because this was not the primary reason for the lack of shame. The lack of shame they felt was from the lack of knowledge. When they gained knowledge from eating the forbidden fruit, this became the very first time that Adam and Eve knew, without being told, that it wasn't OK to be walking around naked in the garden. Not only did they make a covering for themselves from leaves but God even help make them a better covering before sending them out of the garden. When babies are born, they have no shame of nakedness because they also have no knowledge of good and evil. They are pure and sinless just like Adam was before that knowledge and sin kicked in.
Adam and Eve's sin of eating the forbidden fruit brought them shame through knowledge. That natural awareness is the reason we all are not walking around naked on the streets today. It's not primarily because some constitution said it is wrong, rather it came natural to Adam to seek some form of covering in a "public" place. Public nudity may be against some laws on paper in this day and age but there was no verbal or written rule that we know of with Adam and Eve. Yet, this was considered wrong by Adam right after the first sin and without being told.
This doesn't mean that Adam and Eve committed a crime or a sin simply because they were naked. There are things that are wrong but not sinful depending on the circumstance. Being angry is not sinful but it can lead to sin if we hold on to it longer than we should. In the same way, walking around naked in your bathroom is not a sin. However, walking around naked can lead to sin if you find yourself walking around naked in public or somewhere like a strip club.
Lastly, the written Mosaic law that was given through Moses and the verbal Patriarchate laws that came through the fathers of the households were both real laws that existed. Simply because we are not bound by them doesn't mean they didn't exit. The same thing is applicable to what I refer to as the law by nature. And yes, they all cross reference each other one way or another for our learning. As I clarified above, all things pertaining to life and godliness have been revealed.