# When Does a Family Tree Stop Doubling and Begin Shrinking?

The article explains pedigree collapse, where ancestors in a family tree start repeating due to marriages between distant relatives, causing the number of unique ancestors to decline rather than double each generation. This phenomenon is common in human history and affects how we calculate genetic ancestry. It matters because it clarifies why family trees are not simple exponential expansions.

**Importance:** 2/5

## Sources

### Science
- [New Scientist](https://www.newscientist.com/article/2582815-at-what-point-does-my-family-tree-stop-doubling-and-start-decreasing/?utm_campaign=RSS|NSNS&utm_content=home&utm_medium=RSS&utm_source=NSNS) — Wed, 05 Aug 2026 17:00:00 +0000