Our Temples, and the promises we make there are part of that eternal quest.
Today I fielded a call from Wyoming where a person asked, "what is the definition of an ancestor whereby I am to do their family history? They were told by one, just go up your lines.
That's not correct. If I only went up my direct lines, I would have nothing to do but to learn Spanish and crack brick walls. Three of my lines, Cragun, Bingham, and Porter have been researched by faithful genealogist from way back. The Bingham line is back to the 1500's. These are Pioneer lines. People have worked them hard. There are many records they have provided. My other grandparent, Salinas was from Mexico. The records are in Spanish. I don't read Spanish.
The correct answer that is Church policy is easy to understand: Are you blood related? Think of it another way, do you have the same genetic parenthood? If I have a common grandmother or grandfather to another, we are then going to blood related, which can be identified genetically. Church leaders recommend concentrating family history research and temple work on our own ancestors. That, by the way, is one of the sobering facts about DNA. I have my ancestors DNA as a part of mine. You my cousins with the same grandparents have that DNA also. It is remarkably remarkable.
Do you think the creator of all this is in charge? DNA science alone testifies to me of the reality of a Loving God. An accident, I think not. One of the least interested in Church was a man I knew well. He was an Ophthalmologist, an eye surgeon. He couldn't be bothered with religion. He confused me one day as I entered his office. An old Indian man was walking out the door to his car. The Dr. grabbed me by the arm, took me to the door, and pointed at him. "Do you see that man", he asked? Yes I said. "Two weeks ago he was blind, he was blind until I operated on him." That is awesome I said. "It wasn't me. I know it wasn't me. There was something about the operation that I knew I was being guided by a higher being." Wow! And no time or interest in God.
Back to who is my ancestor in LDS policy. An example of one who is not my ancestor for our church responsibility would be the wife of my great grandfathers son. That then would include her parents and grandparents, and up the tree. Their children are my blood relatives.
That's the good news. Yes, there is a lot of research to do.