How far back can you trace your genealogy?
Somewhere between 2,000 and 5,000 years ago, according research done by Steve Olson and Joseph Chang, there was a single person who was the last individual on the planet to be the direct ancestor of every person alive today, all 6.5 billion of us.
They can’t narrow down exactly who he or she was, but whoever it was most likely lived somewhere in eastern Asia, perhaps Malaysia or Siberia.
Olson, a computer scientist, wrote a book in 2002 that maps human history all the way back to our ancient African ancestors that lived more than 100,000 years ago. Yang is a statistician from Yale who started thinking about who might have been the last person on earth to have been a direct ancestor of us all, and when he or she may have lived.
The two scientists teamed up and, with the help of a supercomputer, calculated with mathematical certainty that everyone alive today is a distant relative of a single person that lived sometime in history. And that time frame, they determined, was not that long ago, no more than 5,000 years and more likely closer to 2,000 years.
The details are esoteric and confusing to most of us. But, broken down to its simplest terms, here’s how it works.
Everybody has two parents, four grandparents, and eight great-grandparents. That’s three generations. Now keep going back and you will see that each generation will have double the number of ancestors as the generation that came after it. You had 16 great-great-grandparents, 32 great-great-great-grandparents, and so on.
Now, as an analogy, let me digress a bit. Suppose you have a whole sheet of newspaper laid out flat on the table. Now, fold it in half, then in half again, then in half again. Keep going. After you have folded it 100 times, how thick do you predict it would be?
Would it be as thick as a phone book? How about an unabridged dictionary? Maybe you think it would be as thick as your house is high. The fact is, it would be thicker than the known universe. Go ahead, try it. You’ll never make it close to 100 doublings.
Now apply that principal to the number of generations you would have to go back to encompass all the people on earth. After 40 generations, you’ll find that you will have had over a trillion ancestors. That would put you somewhere in the ninth century CE.
The problem is there were only about 200 million people alive back then. There are not even a trillion of us on earth today. So where did all those extra ancestors come from?
The answer, of course, is that the same person appears on our ancestral family tree more than once. The same person who sired your father’s 25th great-grandfather may also have sired your mother’s 25th great-grandmother.
Since not everyone alive in the ninth century had children, and others had family lines that died out, it turns out that every person who had a continuous family line from the ninth century appears on everyone’s family tree thousands of times.
Going back further in time, you’ll reach a point, about 7,000 years ago, when everyone alive (who had children that continued their line) was an ancestor of everyone alive today.
It’s fascinating, but what does it all mean. Is it just some mathematical hocus pocus?
Well, it’s mathematically sound. Everyone on earth actually did come from one common ancestor who lived somewhere in Asia about 3,000 years ago or so. But it also means that every Muslim is related by blood to every Jew. It means that every black is related by blood to every Neo-Nazi. And every fundamentalist Christian is related by blood to every atheist.
It makes one wonder how we turned out so different.