Wednesday, 24 December 2008

Christmas Eve: Ancestral Arithmetic

Christmas is traditionally a time for ghost stories. But, instead of something spooky and scary, I'm going to tell you about something you may, like me, find oddly comforting.

You have probably heard this factoid at some time: "75% of all the people who have ever lived are now currently alive." Given our worries about overpopulation, it sounds very convincing, doesn't it? And, if you have the remotest vestige of a belief in fairy godmothers or benevolent ancestral spirits, it must also make you think: perhaps they're a wee bit overworked?

It's not true, however. Let me point you towards an article in Scientific American (1st March 2007) which concludes that, according to the calculations of demographer Carl Haub, the living will never outnumber the dead. Far from 75% of all humans being alive now, he makes it about 6%. There have been 100 billion humans, of whom around 6 billion are currently living. So, the supply of Guardian Angels is not only guaranteed, we've got enough to have several on our case at any time, with several more taking a nap. Good news in troubled times!

Actually, that calculation (and that figure of 6%) chimes with another article I read, on a related topic, this time in New Scientist (27th January 2007). This looked at the faulty maths behind most genealogical calculations, which multiply the generations in a too simple-minded way, ignoring overlaps between families, marriages between cousins, etc. For example, someone once calculated that Prince Charles has 262,142 ancestors in 17 generations. But when these were investigated, only a much smaller number of real individuals were found; astonishingly, a mere 6%, in fact. "The difference was due to duplication by intermarriage. So the number of ancestors was only 6% of what might have been expected. The proportionate reduction increases the further back you look. Go back far enough and we're all twigs at the bottom of the same tree."

Mash those two stories together, and you've got yourself a Brief History of Humanity. Although we do have to hope that these two scholars, tunnelling towards each other through a mountain of supposition, have each taken the other's methodology into account, and will meet in the middle ...

But, as this is a Christmas Eve post, what all this really puts me in mind of is James Joyce's great short story, The Dead. Here is its justly celebrated ending:

Yes, the newspapers were right: snow was general all over Ireland. It was falling on every part of the dark central plain, on the treeless hills, falling softly upon the Bog of Allen and, farther westward, softly falling into the dark mutinous Shannon waves. It was falling, too, upon every part of the lonely churchyard on the hill where Michael Furey lay buried. It lay thickly drifted on the crooked crosses and headstones, on the spears of the little gate, on the barren thorns. His soul swooned slowly as he heard the snow falling faintly through the universe and faintly falling, like the descent of their last end, upon all the living and the dead.

I can't follow that. Have a happy Christmas, and an exceptionally good New Year!

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