Legal Question in Constitutional Law in District of Columbia

Re: Origins of areas of law.

No, but it is a major one. The Constitution itself includes treaties (alongside with the Constitution) as "the supreme law of the land." But the law had begun originating before the Constitution. The "common law" developed in England and was adopted here as a body of law developed case-by-case, as courts resolved legal disputes. Sometimes, the Constitution itself is interpreted with reference to what the common law was at the time the Constitution was ratified. For example, when considering whether the First Amendmet right of freedom of speech meant there could be no laws prohibiting obscene speech, the Supreme Court considered the fact that some states prohibited obscene speech at the time the First Amendment was adopted, and (as silly as it sounds) concluded that obscene speech was not the kind of "speech" the framers of the First Amendment had in mind.

For an excellent examination of the importance of pre-Constitution legal principles, I recommend Professor Charles Black's little book, A New Birth of Freedom, in which he argues persuasively that the Declaration of Independence was itself a source of law that should inform our interpretation of the Constitution. ("We hold these truths to be self-evident, that all men are created equal and endowed by their Creator with the inalienable right to life, liberty and the pursuit of happiness", if I remember it right). Black argues that when the Constitution says that the rights not conferred to one of the the government are reserved to the People, it means the full measure of the right to the pursuit of happiness -- a basic legal principle declared at the founding of our nation (or better said, at the founding of the revolution that gave birth to our Nation), our common cause, our point of common agreement as a self-governed people.

But I'm just a lawyer, not a legal historian. I'd be willing to bet that a librarian at your local law school would be happy to direct you to better answers to this question.