I thought you might enjoy this short video asking the question, "What is an ancestor?" But there is a real issue here. Who do you consider your ancestors to be? If you believe the results of some of the online programs that show your relationship to famous people, you could consider anyone who had died as your ancestor. On the other hand, there are those that consider only their direct surname line as "real" ancestors. Is there a generally accepted definition of "ancestor?" Or is the issue so clouded by social and cultural attitudes as to be meaningless?
Kinship, in the context of anthropology, is the study of the patterns of social relationships in human cultures. You could say that anthropology looks at the pattern and genealogy looks at the identity of the people in the pattern. In the Western European genealogical tradition, we have imposed a strict structure on our relationship patterns through the use of the "standard pedigree chart." While at the same time, we pay lip service to other non-traditional patterns. In a real sense, the patterns expressed by the more popular genealogical database programs, to some extent, mandate our view of these relationships.
As genealogical interests expand beyond their core Western European established patterns into cultures that do not share the same kinship patterns, there is a real question as to whether or not some "standard" worldwide pattern should be imposed. Most current genealogical database programs presently allow for multiple parent relationships, i.e. biological, adoptive, foster, guardianship etc. But even with this expansion of the core relationships in families, there are other patterns that do not fit into any of these categories. One notable exception, from Western European culture, is the existence of godparents.
It should be obvious that in our present society, focusing on the biological lineage alone is impractical and in some cases impossible.
In a larger sense, there is also the issue of who in your pedigree is considered to be a "relative" and who is not. In our American culture, spouses are seldom closely related. Quite commonly, I get into a discussion with people about their ancestors and begin with the question as to whether or not they are "related" to their husband or wife? In my case, for example, I have yet to find any common ancestor between my own family and my wife's family. On the other hand, my own parents were second cousins. They had great-grandparents in common.
Here is a question that illustrates the issue. Are you related to your siblings' spouses? Granted, your children and their children are cousins, but are you related to your brother or sister-in-law? I don't happen to consider my in-laws as relatives. I have no interest in researching their lineage and do not feel compelled to record information about their ancestors. But my attitude in this regard is ambiguous and inconsistent. If I go back a generation or two, I have traditionally included all of the lines from all of the spouses of some of the siblings in any particular generation in my database. For example, if I go back to my Great-grandfather, Henry Martin Tanner, I have recorded all of his biological children (my aunts and uncles and my Grandfather) and all of their spouses. In some cases, I have traced the spousal lines and in some cases, I have not. Am I missing a set of my own "ancestors" by omitting all of the possible lines? Some of my ancestors had multiple marriages. Do I include all of the spouses' families, even those I am not "related" to?
The issue of multiple spouses is not unique to those of us descended from polygamist families. Many of my ancestors had multiple marriages with children from each marriage due to the death of a spouse or divorce.
For those who are members of The Church of Jesus Christ of Latter-day Saints (LDS), this issue takes on an added dimension when we consider our responsibility for performing proxy ordinances for our deceased relatives. There are very specific guidelines to determine who is and who is not a "relative" in this context.
I think this issue of who is a relative is mostly ignored by the genealogical community. Not because the issue doesn't exist, but because we are like fish swimming in the water. We don't question the water. It is just there. We don't question the system. It is just there. But maybe we need to examine how we define our system so that we can communicate on the same level with different kinship systems.