Pedigree collapse is a term created by Robert C. Gunderson to denominate the collapse of the family trees caused either by of close cousin marriages or distant cousins unknowingly getting married.
If we assume that there is a new generation each 25 years, over 600 years a single person can have up to 224 or roughly 16 million possible ancestors. But if go back another 600 years (to 800AD), that will get us 248. That would be 281.5 trillion grandparents, far more people than have existed throughout the history of humanity.
The catch is that ancestors along the way married their cousins, often without knowing it but in many cases intentionally. This is pedigree collapse; the closer the cousin, the bigger the percentage of the collapse. Of course the worst case is when two siblings got married (think royalty-wise for instance) when it is a 50% collapse. With a first cousin, it is a 25 percent collapse, and so on.
In some cultures, cousins were encouraged or required to marry to keep kin bonds, wealth and property within a family. Among the royalty, the frequent requirement to only marry other royals resulted in a reduced gene pool where most individuals had extensive pedigree collapse. Alphonso XII, for example, had only eight great-great-grandparents instead of the usual sixteen. Isolated populations such as remote islanders represent extreme examples of pedigree collapse but the ordinary tendency to marry those within easy walking distance along with the relative immobility of the population before modern conveniences meant that most marriage partners were distantly related. Even in America, the tendency of immigrants to marry among their ethnic, language or cultural group produces many cousin marriages.
Demographer Kenneth Wachtel estimated that for a typical English child of the mid-20th century, at the time of Columbus, 95 percent of his ancestors would have been different individuals and 5 percent duplicates. At the time of the Black Death, an average of 70 percent would have been duplicates.
The maximum number of ancestors for most people is likely to occur around 1200 AD. Some geneticists believe that everybody on earth is at least 50th cousin to everybody else.
See also
External links
Source
- The Mountain of Names by Alex Shoumatoff (1985).