With the advent of the human genome project and the advances in gene sequencing. It is entirely possible to track down all of your ancestors even if nobody knows what their names might have been. If a few specific mutations to gene 10 from your great great grandfather are passed down to everybody who gets his gene 10, then everybody with that mutation is an descendant of that person. It would be completely possible to track down exactly how related you are to your spouse, 5th cousins or 50th cousins. It will soon be possible to trace down the family trees of those individuals who lost their family traveling to their new homes whether on a ship whose registry was lost or a slave ship being ripped from their homelands.
Within our lifetimes, we could compose a family tree for all of mankind. Unless we decide to engage in the grand mass murder of our cousins before we can do so.