Do We Have an Endless Supply of Cousins?

I received the following comment:

I have been enjoying your blogs and, I too, have mixed feelings about Church members rushing to find names for the temple without careful checking for duplication, etc. As you know, there has been a recent emphasis on the finding of cousins for this purpose by descendancy & Puzzilla research, etc. With half of my ancestry being non-LDS, I have been fairly successful in finding temple names by these and associated methods. I realize that it may not be this easy for some church members with long LDS pioneer ancestry on all lines with much of the work already done.

I was looking in your blogs to find one which addressed this cousin searching issue. For most church members, would you estimate that there are hundreds &/or thousands of searchable (i.e., in the 1700-1904's) non-member cousins in the spirit world waiting to have their temple work done? After a couple of years of intensive Puszzila research by many church members, perhaps the number of available temple names would be reduced. Of course, that would be good and probably other effective searching tools will emerge not to mention of new members coming into the Church continually around the world.

There is a rule of genealogy called "Pedigree Collapse." From Wikipedia: Pedigree collapse:

In genealogy, pedigree collapse describes how reproduction between two individuals who share an ancestor causes the number of distinct ancestors in the family tree of their offspring to be smaller than it could otherwise be. Robert C. Gunderson coined the term, which is also known by the German term Ahnenschwund (loosely translated: loss of lineage) or the term implex.

 If this were not the case, then going back 30 generations would mean that you had over a billion ancestors, which would be more than the entire population of the earth at the time. Additionally, any genealogist who has done a significant amount of genealogy has probably reached an "end of line" situation where it seems to be impossible to continue finding additional ancestors. But the current population of the earth is around 7.1 billion and each one of those people has ancestors. How do we reconcile the current population with pedigree collapse?

The answer is pretty clear, all of us have common ancestors. But a less obvious answer is that we have many more relatives who are descendants of our common ancestors than we do ancestors. Let's imagine that we are tracing our ancestral lines back to the mid-1800s. For some younger people, that might be as much as ten generations. For some very old people, that might be only three generations. But how many relatives might you have who are descendants of those mid-1800s ancestors?

The answer to that question will depend on the number of children but that number was calculated for one of my ancestors for a book published in 1982. My Great-great-grand father would presently have tens of thousands of descendants. There is really no end to all the potential cousins I might have. Every generation I go back potentially increases the number by thousands and thousands of descendants on any one line. The pool of potential cousins will increase at the rate that presently living people extend their genealogy back a few generations. Extending your pedigree even one more generation along only one line increases the pool of potential cousins by an enormous number.

At the present rate of participation in family history, we don't have to worry too much about running out of cousins.