Human nature, at that time solely existed in Adam and was created as being in the covenant of works. Adam didn't enter into the covenant of works subsequent to his creation but was created in this covenant. So he was in the covenant of works from the very instant of his existence.
At the very instant he formulated his first thought he was conscience of God and the covenant, he knew nothing else.
Therefore Jim, "the human nature" in its totality, as well as the entire human race in Adam, were created in this covenant. Are you following so far? This is important if you are to understand.
Therefore, all people are stillborn within the covenant of works. So, do you understand, upon Adam's breach of the covenant, "the human nature", in its totality, that is "the entire human race", broke the covenant.
So, it is, therefore, righteous that this nature of the human race is rendered guilty, and that every human being, every person, by virtue of having this same nature, has the covenant breach imputed unto him and is deemed worthy of condemnation.
So, it's only Adam's breach of the covenant and not his subsequent sins that are imputed to his posterity. And it's not only because we all are partakers of the same nature as Adam but because we were created in the covenant of works in Adam and we have all broken it in him.
@JIM I Hope you understand this and stop making silly accusations.