# Generational collapse **URL:** \ **Category:** Factual Questions\ **Created:** [June 3, 2011, 11:35pm UTC](https://boards.straightdope.com/t/generational-collapse/584261 "2011-06-03T23:35:42Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![Patrick\_Mc](https://avatars.discourse-cdn.com/v4/letter/p/5e9695/32.png) [@Patrick\_Mc](https://boards.straightdope.com/u/Patrick_Mc)\ **Post date:** [June 3, 2011, 11:35pm UTC](https://boards.straightdope.com/t/generational-collapse/584261/1 "2011-06-03T23:35:42Z")
What is generational collapse? How often does it occur? ---
**Author:** ![JWT\_Kottekoe](https://avatars.discourse-cdn.com/v4/letter/j/3ec8ea/32.png) [@JWT\_Kottekoe](https://boards.straightdope.com/u/JWT_Kottekoe)\ **Post date:** [June 4, 2011, 1:43am UTC](https://boards.straightdope.com/t/generational-collapse/584261/2 "2011-06-04T01:43:36Z")
Are you talking about pedigree collapse? > **[Pedigree collapse](https://en.wikipedia.org/wiki/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; synonyms include implex and the German Ahnenschwund (loosely translated: "loss of lineage"). > Without pedigree collapse, a person's ancestor tree is a binary tree, formed by the person, the parents (2), the grandparents (4), great-grandpar... It always happens. It just means that the number of our ancestral parents N generations back is smaller than 2^N, as you might naively expect. The reason is that there are many duplications in the list of 2^N names, because of in-breeding. If your pedigree didn’t collapse, you’d have trillions of ancestors 1,000 years ago and there were far less than a trillion people alive at that time. ---
**Author:** ![JWT\_Kottekoe](https://avatars.discourse-cdn.com/v4/letter/j/3ec8ea/32.png) [@JWT\_Kottekoe](https://boards.straightdope.com/u/JWT_Kottekoe)\ **Post date:** [June 4, 2011, 1:46am UTC](https://boards.straightdope.com/t/generational-collapse/584261/3 "2011-06-04T01:46:21Z")
If you were talking about pedigree collapse, I see that the master himself has addressed this question: > **[2, 4, 8, 16 … how can you always have MORE ancestors as you go back in time?](https://www.straightdope.com/21341588/2-4-8-16-how-can-you-always-have-more-ancestors-as-you-go-back-in-time)**