"Pedigree collapse" due to inbreeding

"Pedigree collapse" due to inbreeding -- Genealogists use the term "pedigree collapse" (coined by Robert C. Gunderson) to signify the phenomenon that if you go back enough generations in your family tree, the number of unique individuals is less than the number of slots due to inbreeding so ancestors end up doing double duty as redundant forebears. The number of unique individuals per generation in your family tree forms roughly a diamond shape, expanding for a number of generations into the past, then collapsing the farther back you go.

The term "pedigree collapse" almost never ever comes up in discussions of race because American intellectuals don't grasp that race should be thought about in genealogical terms, but it's useful for understanding how racial groups are formed and fade away.

If you go back to ancestors alive 4,000 years ago, say, George W. Bush might indeed by descended by 1 path from n!Xao, a Bushman in the Kalahari, but he'd also be descended from Owen, a farmer in Essex, by 800,000,000 different paths. Add them all up and it's reasonable to say that George W. Bush is a lot more British than Bushman. Nobody actually doubts that, but when people like Steve Olson start talking about genealogy, they quickly get bogged down in essentially symbolic thinking, in which having one ancestor from ethnic group X is somehow just as important as having many millions from ethnic group Y.

Here's an interesting description of pedigree collapse from John Becker:

We all are blessed with two parents, four grandparents, eight great grandparents and so on. If the average generation is twenty-five years, in 1200 years (back to 800 AD, the time of Charlemagne) each person has 281.5 trillion grandparents. That's the way geometric progressions work. The number of grandparents doubles every 25 years and in 12OO years or 48 generations, 281.5 trillion names would be on your pedigree.

But hold on, you say! In 800 AD there were not that many people on the whole planet. How could I - or any person - have that many grandparents? The answer is that while you must have this number of grandparents, given the imperatives of human procreation, they are not all different people. Some names on your pedigree appear twice, three times or even hundreds of times in the 1200 years.

Cousins have married and, if they were first cousins, their offspring will have only six great grandparents rather than the normal eight. Those offspring will have pedigrees which have "collapsed" from 8 to 6 or 25% in the 4th generation back. That 25 % collapse will be present in each and every one of the 44 generations back to 800 AD. The same phenomenom occurs when 2nd, 3rd, 4th or 5th cousins marry although the percentage ‘collapse’ is not as dramatic. A dramatic collapse occurs when siblings marry as was the norm for Egyptian pharaohs and Inca kings. In those cases there is a 50% collapse (from 4 to 2) at the 3rd generation, the grandparents...

- King Alfonso XIII of Spain (1886-1941) had only eight different people as his great great grandparents rather than the normal sixteen, a 50% collapse of his pedigree at the 5th generation. [Cecil Adams says 10, not 8 unique gg grandparents.]

- Prince Charles' pedigree has been examined by Gunderson who found that 17 generations back when Charles should have had 65,536 progenitors, he only had about 23,000, a collapse to 35 % of the theoretical.

- A great deal is known about the family histories of the Amish who came to North America from Switzerland in the 18th century. It is estimated for one family about whom a very complete genealogy has been compiled that 21.5 % of 627 marriages in this family were between 2nd cousins or closer.

- Mr. K. W. Wachtel, a demographer cited by Shoumatoff, built a probability model for a child born in England in 1947. Around the time of King John who reigned from 1199 AD to 1216 AD, this 1947 child would have about two million grandparents in the same generation. This represents about 37% of the progenitors required 30 generations back. This is the first type of pedigree ‘collapse’ that occurs. The child would be descendant from 80% of all the people in England at that time.

- But now a ‘collapse’ in the absolute number of progenitors starts to occur for this 1947 child. The actual number of different grandparents would start to decrease at this point - 30 generations back. Theoretically the further one goes back from this point the smaller the number of different grandparents there would be until one reached one's theoretical ‘Adam and Eve’. Put in graphical terms and viewing the child's pedigree from the bottom (now) to the top (early), the number of names creates a diamond with one person at the bottom in 1947, two million people in the generation 700 years earlier and then an ever-decreasing number dwindling to the original ‘Adam and Eve’, say, several thousands of years before that at the very top of the chart.

Alex Shoumatoff''s 1985 book A Mountain of Names introduced Gunderson's concept of pedigree collapse to a broader public. Shoumatoff quotes prominent anthropologist Robin Fox (co-author with the similarly animalistically-named anthropologist Lionel Tiger):

"If we could only get into God's memory, we would find that eighty per cent of the world's marriages have been with at least second cousins," the British social theorist Robin Fox told me recently. "In a population of between three and five hundred people, after six generations or so there are only third cousins or closer to marry. During most of human history, people have lived in small, isolated communities of about that size, and have in fact probably been closer to the genetic equivalent of first cousins, because of their multiple consanguinity. In nineteenth-century rural England, for instance, the radius of the average isolate, or pool of potential spouses, was about five miles, which was the distance a man could comfortably walk twice on his day off, when he went courting- his roaming area by daylight. Parish registers bear this out. Then the bicycle extended the radius to twentyfive miles. This was a big shakeup." Even in today's much more mobile English society-according to an estimate in Fox's book "Kinship and Marriage"-the average isolate for any given individual, which is "to some extent determined by the previous marriage choices of his ancestral consanguines," varies from about nine hundred people to just over two thousand.

My published articles are archived at iSteve.com -- Steve Sailer