An origin point? I guess I would have to say early 70's if I had to pin it down.
There is only a single deterministic Universe so no verification needed.
It has a head, two arms, two legs, and a couple dangly bits.
I lived in a community of Nazis that were experimenting on me and my best friend.
In the 70's and 80's the Reich (a secret Nazi state within the USA) was given a set of video tapes, audio tapes, and written transcripts that were purported to be the vision and voice of God. Turns out they were the memories of an individual from the future (yours truly) committed to physical medium. Because I also existed in the past, I was able to interact with those memories and they functioned as windows into the future.
Think of it this way - in the past, I'm watching the video and remembering what the guy in the video is saying. In the future, I'm remembering what the guy in the future said and what I thought in response and I'm able to formulate my response taking into account my thoughts from that moment in time. See also: the Blink conversation from Doctor Who, the dinner part conversation from The Time Traveler's Wife.
Ancient Greece, Germany in the 30's, the dawn of time, Sherwood Forest, several dead-end alternative futures.
I have had sex. Pretty normal sex drive, maybe on the high end.
It's sweet.