Can you marry your relative?

Can you marry your relative? According to the Bible all people on earth go back to Noah's family, and before that, back to Adam and Eve. Since we are all ultimately the descendants of the same parents, all people are related. You have to marry your relative! If you don't, you marry something that isn't human. Of course, today we don't marry our close relatives for legal and biological reasons. We marry someone further away in relation to us.