I AM not adopted; I have mysterious origins.
I have said that sentence many times in the course of my life as an adopted person. I like it so much I put it into the mouth of a character in the novel I'm writing. The character and I are both fond of the idea. We can think of ourselves as living in the dense pages of 19th-century fiction, where one's origins -- the exact mother and father -- are not nearly as important as one's "circumstances."
Some might say I came to this rationalization because, until recently, everything surrounding my adoption was kept secret from me. Even the date it was finalized was a secret. (The woman on the phone said, "Those records are sealed." I said, "I know I can't see what's in them, but can I find out the date from which I couldn't see what's in them?" She replied, "Even the outsides of the records are sealed" -- a confounding statement, as I envisioned envelopes surrounding envelopes, all sealed into infinity.)
Of course, mysterious origins are a confusing business these days. One might be gestated in an unknown womb while having genes from some combination of one's mother and father and a stranger; from a mother's womb with some combination of known and unknown genes -- not to mention the complication of untold numbers of half-siblings who might be out there from the sperm donations of one man. There are adoptive parents and biological parents, surrogates and donors -- adults of all sorts claiming parenthood by right of blood, genes, birth, law and affection.