The Sons of Noah
"The sons of Noah who came out of the ark were Shem, Ham and Japheth. (Ham was the father of Canaan.)These were the three sons of Noah, and from them came the people who were scattered over the earth...Genesis 9
By MATT CRENSON AP National Writer
Joseph Anton Koch (1768 - 1839)
Jul 1, 2006 (AP)— Whoever it was probably lived a few thousand years ago, somewhere in East Asia. Taiwan, Malaysia and Siberia all are likely locations. He or she did nothing more remarkable than be born, live, have children and die.
Yet this was the ancestor of every person now living on Earth, the last person in history whose family tree branches out to touch all 6.5 billion people on the planet today.
That means everybody on Earth descends from somebody who was around as recently as the reign of Tutankhamen, maybe even during the Golden Age of ancient Greece. There's even a chance that our last shared ancestor lived at the time of Christ.
"It's a mathematical certainty that that person existed," said Steve Olson, whose 2002 book "Mapping Human History" traces the history of the species since its origins in Africa more than 100,000 years ago.
It is human nature to wonder about our ancestors who they were, where they lived, what they were like. People trace their genealogy, collect antiques and visit historical sites hoping to capture just a glimpse of those who came before, to locate themselves in the sweep of history and position themselves in the web of human existence.
But few people realize just how intricately that web connects them not just to people living on the planet today, but to everyone who ever lived.
With the help of a statistician, a computer scientist and a supercomputer, Olson has calculated just how interconnected the human family tree is.
You would have to go back in time only 2,000 to 5,000 years and probably on the low side of that range to find somebody who could count every person alive today as a descendant.
Furthermore, Olson and his colleagues have found that if you go back a little farther about 5,000 to 7,000 years ago everybody living today has exactly the same set of ancestors.
In other words, every person who was alive at that time is either an ancestor to all 6 billion people living today, or their line died out and they have no remaining descendants.
That revelation is "especially startling," statistician Jotun Hein of England's Oxford University wrote in a commentary on the research published by the journal Nature.
"Had you entered any village on Earth in around 3,000 B.C., the first person you would have met would probably be your ancestor," Hein marveled.
It also means that all of us have ancestors of every color and creed. Every Palestinian suicide bomber has Jews in his past. Every Sunni Muslim in Iraq is descended from at least one Shiite. And every Klansman's family has African roots.
It's simple math. Every person has two parents, four grandparents and eight great-grandparents. Keep doubling back through the generations 16, 32, 64, 128 and within a few hundred years you have thousands of ancestors.
It's nothing more than exponential growth combined with the facts of life. By the 15th century you've got a million ancestors. By the 13th you've got a billion. Sometime around the 9th century just 40 generations ago the number tops a trillion.
But wait. How could anybody much less everybody alive today have had a trillion ancestors living during the 9th century? The answer is, they didn't.
Imagine there was a man living 1,200 years ago whose daughter was your mother's 36th great-grandmother, and whose son was your father's 36th great-grandfather. That would put him on two branches on your family tree, one on your mother's side and one on your father's.
In fact, most of the people who lived 1,200 years ago appear not twice, but thousands of times on our family trees, because there were only 200 million people on Earth back then. Simple division a trillion divided by 200 million shows that on average each person back then would appear 5,000 times on the family tree of every single individual living today.
But things are never average. Many of the people who were alive in the year 800 never had children; they don't appear on anybody's family tree. Meanwhile, more prolific members of society would show up many more than 5,000 times on a lot of people's trees.
Keep going back in time, and there are fewer and fewer people available to put on more and more branches of the 6.5 billion family trees of people living today. It is mathematically inevitable that at some point, there will be a person who appears at least once on everybody's tree.
But don't stop there; keep going back. As the number of potential ancestors dwindles and the number of branches explodes there comes a time when every single person on Earth is an ancestor to all of us, except the ones who never had children or whose lines eventually died out.
And it wasn't all that long ago. When you walk through an exhibit of Ancient Egyptian art from the time of the pyramids, everything there was very likely created by one of your ancestors every statue, every hieroglyph, every gold necklace. If there is a mummy lying in the center of the room, that person was almost certainly your ancestor, too.
It means when Muslims, Jews or Christians claim to be children of Abraham, they are all bound to be right.
"No matter the languages we speak or the color of our skin, we share ancestors who planted rice on the banks of the Yangtze, who first domesticated horses on the steppes of the Ukraine, who hunted giant sloths in the forests of North and South America, and who labored to build the Great Pyramid of Khufu," Olson and his colleagues wrote in the journal Nature.
These are some of artifacts writer and editor Steve Olson uses to trace his family's genealogy and create a family tree, pictured March 13, 2006, at Olson's home in Bethesda, Md. (AP Photo/Haraz N. Ghanbari)Click and Drag Photo to resize.
Plugging the planet's current population into his equation, he came up with just over 32 generations, or about 900 years.
Chang knew that answer was wrong because it relied on some common, but inaccurate, assumptions that population geneticists often use to simplify difficult mathematical problems.
For example, his analysis pretended that Earth's population has always been what it is today. It also assumed that individuals choose their mates randomly. And each generation had to reproduce all at once. Chang's calculations essentially treated the world like one big meet market where any given guy was equally likely to pair up with any woman, whether she lived in the next village or halfway around the world.
Chang was fully aware of the inaccuracy people have to select their partners from the pool of individuals they have actually met, unless they are entering into an arranged marriage. But even then, they are much more likely to mate with partners who live nearby.
And that means that geography can't be ignored if you are going to determine the relatedness of the world's population.
A few years later Chang was contacted by Olson, who had started thinking about the world's interrelatedness while writing his book. They started corresponding by e-mail, and soon included in their deliberations Douglas Rohde, a Massachusetts Institute of Technology neuroscientist and computer expert who now works for Google.
The researchers knew they would have to account for geography to get a better picture of how the family tree converges as it reaches deeper into the past. They decided to build a massive computer simulation that would essentially re-enact the history of humanity as people were born, moved from one place to another, reproduced and died.
Rohde created a program that put an initial population on a map of the world at some date in the past, ranging from 7,000 to 20,000 years ago. Then the program allowed those initial inhabitants to go about their business. He allowed them to expand in number according to accepted estimates of past population growth, but had to cap the expansion at 55 million people due to computing limitations.
Although unrealistic in some respects 55 million is a lot less than the 6.5 billion people who actually live on Earth today he found through trial and error that the limitation did not significantly change the outcome with regard to common ancestry.
The model also had to allow for migration based on what historians, anthropologists and archaeologists know about how frequently past populations moved both within and between continents. Rohde, Chang and Olson chose a range of migration rates, from a low level where almost nobody left their native home to a much higher one where up to 20 percent of the population reproduced in a town other than the one where they were born, and one person in 400 moved to a foreign country.
Allowing very little migration, Rohde's simulation produced a date of about 5,000 B.C. for humanity's most recent common ancestor. Assuming a higher, but still realistic, migration rate produced a shockingly recent date of around 1 A.D.
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