There are a few particularly interesting points when you go back up your ancestor tree. First, there is a point where some ancestor of yours is an ancestor of everyone else currently living (and so will also be an ancestor of everyone else to come). This is the "most recent common ancestor" point. Go farther back and you reach the "identical ancestors point" (also known as the "all common ancestors point" or the "gen…
Thank you, I learned a lot from your comment. It also occurred to me that since only about half of a parent's genes are passed on, a person can have had Neanderthal ancestry and for whatever reason the Neanderthal genes were not passed on.
I think it is better to speak of uniquely Neanderthal genes. Our genome must have been almost identical to the Neanderthal genome, given that interbreeding was both possible and that the hybrid offspring remained fertile. So it is likely that many people alive today do indeed have genes from the Neanderthal line, but those genes are either identical to human genes or so close that we cannot distinguish their Neanderthal original from ordinary variations/mutations.