Thursday, August 23, 2007

Do You Have More Women Ancestors?

The Transylvania Dutch and The Genealogue blogs link to a New York Times blog post by John Tierney titled "Is There Anything Good About Men? And Other Tricky Questions." There is a good discussion here, centered on the thesis that:

"The 'single most underappreciated fact about gender,' he said, is the ratio of our male to female ancestors. While it’s true that about half of all the people who ever lived were men, the typical male was much more likely than the typical woman to die without reproducing. Citing recent DNA research, Dr. Baumeister explained that today’s human population is descended from twice as many women as men. Maybe 80 percent of women reproduced, whereas only 40 percent of men did."

The update by Tierney to his post gives a simple example:

"UPDATE, Noon Tuesday: Before anyone else posts a comment insisting that it’s mathematically impossible for any individual to have an unequal number of male and female ancestors, consider the following Edenic scenario. There are two women (Ginger and Mary Ann) and two men (Gilligan and the Professor) on a deserted island. Both women spurn Gilligan and have a child with the Professor. Ginger has a boy named Gino; Mary Ann has a girl named Maria. When they grow up, Gino and Maria have a child. This child will have three female ancestors (Maria, Ginger and Mary Ann) but only two male ancestors (Gino and the Professor). "

There are comments on this posting, many of them are searching and analytical.

The original comment seems to be based on the fact that fewer men than women had children, and therefore the men that did have children had them by more than one woman. There is also the possibility of inter-generational incest. Pedigree collapse seems to dictate that there was much "inter-breeding" between close or distant family members back before the middle ages. The Wikipedia article on "pedigree collapse" notes:

"Demographer Kenneth Wachtel estimated that for a typical English child of the mid-20th century, 95% of ancestors would have been unique individuals and 5% duplicates at the time of Columbus. At the time of the Black Death, an average of 70% 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."

That's interesting! The Black Death noted was in the 1300's, apparently. Of course, most of the known pedigrees that go back to the 16th century and earlier are for royalty or nobility - and we all know that they really messed around - and probably skewed the perception of the results. For the "typical English child of the 20th century," they cannot fill out a pedigree chart much earlier than 1800 due to the poor records - English and/or American. And sure - everyone probably is a 50th cousin to everybody else - but probably not through the same ancestral line.

So, in the context of "ALL of my ancestors" - those back to when the human species started to expand began - say 800 generations (perhaps 20,000 years ago?) or more (realize that 100 generations - about 2,500 years - is 1 nonillion potential ancestors on the pedigree chart - 1 followed by 30 zeroes, and 800 generations would be 1 followed by 240 zeroes) - the initial hypothesis that I have twice as many different female ancestors as male ancestors is probably correct, since I only have a potential of 1 million ancestors in 20 generations (about 500 years), but I have a potential 1 trillion in 40 generations (about 1,000 years) (all numbers rounded off). That boggles the mind, eh?

However, most of us think about this only in "modern history" terms - the last 200 to 400 years. In that context, my educated guess is that less than 1% of my male ancestors since 1600 (perhaps 32,000 potential ancestors, total) fathered children by different female ancestors. I know of one case in my ancestry - where a male (Adam Mott) had children by two wives in the 1600's that are both in my ancestral line. Obviously, there may be special cases in the last 400 years where more women than men appear in a pedigree - a fellow like Brigham Young who had children by many wives, and surely some of those children inter-married, comes to mind.

Frankly, I feel real sorry for Gilligan who apparently never knew the joys of Mary Ann and Ginger, except from afar (true confession - I always saw myself as a Gilligan when I was young). And what about the Skipper and Mr. Howell? Would it have been inconvenient or too complex for Tierney to include them in his simple fanciful scenario?

An interesting discussion - thanks to John and Chris for the link. I even had to use my engineering calculator!

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