Skip to comments.Human populations are tightly interwoven
Posted on 09/30/2004 11:17:34 AM PDT by AZLiberty
The most recent common ancestor of all humanity lived just a few thousand years ago, according to a computer model of our family tree. Researchers have calculated that the mystery person, from whom everyone alive today is directly descended, probably lived around 1,500 BC in eastern Asia.
Douglas Rohde of the Massachusetts Institute of Technology in Cambridge and his colleagues devised the computer program to simulate the migration and breeding of humans across the world. By estimating how different groups intermingle, the researchers built up a picture of how tightly the world's ancestral lines are linked.
The figure of 1,500 BC might sound surprisingly recent. But think how wide your own family tree would be if you extended it back that far. Lurking somewhere in your many hundreds of ancestors at that date is likely to be somebody who crops up in the corresponding family tree for anyone alive in 2004.
In fact, if it were not for the fact that oceans helped to keep populations apart, the human race would have mingled even more freely, the researchers argue. "The most recent common ancestor for a randomly mating population would have lived in the very recent past," they write in this week's Nature1.
To work out how much different groups of humans mingled, Rohde's team simulated the rates at which a few pioneering people made journeys across the world to meet and breed with other populations. Their model gave each individual a certain probability of quitting their home town, country or continent and striking out for pastures new.
They were then able to name a time and place at which our most recent common ancestor lived. But who was this person? He or she must have had a flourishing family, says Rohde. "Maybe it was someone who happened to have 40 children or some such astronomical number," he says. "But it could equally have been someone with above-average productivity for a few generations." Instead of two kids, Rohde suggests, maybe the person and his or her direct descendants had three.
The fact that the person probably lived in Asia is down to its prime position along the most commonly used migration routes, Rohde suggests. "East Asia is at a crossroads," he says. "It's close to the Bering Strait and the Pacific."
Rohde's simulation aims to include everyone alive today, and therefore relies on the assumption that no population has remained completely isolated for any significant length of time. Rohde is confident that this is the case; even Tasmania, once thought to be isolated by choppy seas, contains no people with purely Tasmanian blood.
If we discount those living in the world's remotest places, the common ancestor becomes more recent still, says Mark Humphrys, who studies human family trees at Dublin City University in Ireland. "Looking at the whole sweep of the Americas, Europe, Asia, right across to Japan, I wouldn't be surprised if we had a common ancestor in the AD years," he says.
A single prolific parent can have a vast influence once their descendants begin to multiply, Humphrys says. "The entire Western world is descended from Charlemagne, for example," he says. "There's really no doubt."
Besides dating our most recent common ancestor, Rohde's team also calculates that in 5,400 BC everyone alive was either an ancestor of all of humanity, or of nobody alive today. The researchers call this the 'identical ancestors' point: the time before which all the family trees of people today are composed of exactly the same individuals.
This recent date is not really surprising either, Rohde says. Anyone whose lineage survived for a few generations was likely to have descendants spread all over the world. At the identical ancestors point, then, our ancestors came from every corner of the globe, although those from far afield are unlikely to have made a significant contribution to our genetic make-up.
Nonetheless, the results show that we are one big family, Rohde says. As he and his colleagues write: "No matter the languages we speak or the colour of our skin, we share ancestors with those 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 laboured to build the Great Pyramid of Khufu."
My ex girlfriend was my cousin? Freaky!
Occasionally yes, or else no human population ...
These computer simulations are even less reputable than mtDNA "studies". It's amazing how thin an ancestry can become. My best friend has no first cousins. He's an only child. His mother was an only child. Her father was orphaned at a young age, losing his parents and only sibling (sister) to an accident, so she had no first cousins.
For that matter... my family has lived on the same farm since 1851, and was in town (although calling it a town at that point was dubious) for about seven years before that. While doing some rudimentary genealogical research, I found another family has lived in the same town for most of that time, and prior to that, in similar proximity to my family, going back hundreds of years in America -- without ever intermarrying (apparently -- I wasn't meticulous).
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First, it's a "simulation"..
Second, it's a "probability model"..
If we were talking Global Warming, we would dismiss it out of hand..
As a civil engineer I can guarantee that every time you walk into a building you're staking your life on both.
The math isn't too hard to follow. We all had two parents, four grand parents, eight-- well, you get the picture. Pat Paulsen said this proves the world population is obviously shrinking, but I think it shows that the world's common ancestry could be as recent as about 30 generations, or 600 years.
Hopkin took this idea a step further and plugged in how much people travel and showed that our common grandpa shouldn't be farther back than 3500 years.
It's "probably" true.
It's probably not true, since there are scads of assumptions in any such a simulation, most of which are probably either untested or untestable. Is it really reasonable to expect that every member of an isolated tribe in the mountains of New Guinea, that had never even seen Europeans (much less intermarried with them) before 1950, shares a recent common ancestor with a family in Iceland that has a complete geneology going back to 800 AD? Not hardly.
I realize that this study is hoakum but this date falls amazingly close to the date of Adam according to some biblical timelines.
If we're talking about physical movement and mathematical probabilities, then we're discussing whether or not the various populations (such as those in New Guinea) were hermetically sealed or was there any movement at all in the last three and a half millinea.
The world population back then was less than 100 million. For you or I to not be descended from cousins there would have had to have been a population of 4,789,048,565,205,902,682,369,834,459,844,000,000, 000,000,000,000,000,000,000. So we both agree that
1. We don't know anything for sure
2. People intermarried a lot
3. People moved around a lot.
We could go at this strictly from Sacred Texts also but (please forgive) I'm not sure where you're coming from.
Depends on how you define "recent".
If we're talking belief systems (i.e. the New Guinea and the Lakota were created separately) then we need to study the Holy Writings... We could go at this strictly from Sacred Texts also but (please forgive) I'm not sure where you're coming from.Keith was talking about genealogies, not Holy Writings or Sacred Texts. Since the authors of the study claim that everyone is descended from a single individual 3500 years ago, and humans have been in the Americas for at least 10,000 years (presumably having ancestry outside the Americas, although Native Americans generally believe their ancestors have always been here), there's obviously very little chance of these study results' being plausible.
If we're talking about physical movement and mathematical probabilities, then we're discussing whether or not the various populations (such as those in New Guinea) were hermetically sealed or was there any movement at all in the last three and a half millinea.Mathematical probabilities don't enter into it -- someone in Eurasia 3500 years ago couldn't be the ancestor of every Native American, even though (in my view) the oceans have been traveled by a huge variety of different cultures for tens (maybe hundreds) of thousands of years.
The world population back then was less than 100 million. For you or I to not be descended from cousins there would have had to have been a population of 4,789,048,565,205,902,682,369,834,459,844,000,000,000,000,000,000,000,000,000. So we both agree that.I know my family lines back (in some cases) ten or twelve generations. I've never found ANY overlapping lines. While it's true that my family seems a little unusual (my grandfather was born in 1875; his grown brother died in 1873; their father was born in 1825; one of our female ancestors from the first American generation died aged at least 100), family lines are unique, sometimes even among siblings. So, yeah, We don't know anything for sure, People intermarried a lot, and People moved around a lot.
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The point Hopkin is highlighting is that since (as we agree) that it's easy to believe that from say, 1500BC to 500BC that at least one guy visited the Americas from Asia, and shared genes. We don't have photos but it's simply not reasonable to say it didn't happen.
Since then, 2,500 / 20 = 125 generations have passed. Remember that this is 125 doublings -- a factor of some 40 digit number. This would spread the guy's genes to every single human in the Americas. This isn't hard to believe considering that it took about that long for the first Eurasians to cover that area. The only way that his family tree would not have spread would be that maybe the guy had some kind of genetic condition where everyone in his family dies at birth (rim shot), or maybe him and the little woman moved to the moon (cow bell).
But seriously folks, not to worry-- I promise not to take advantage of our newly discovered family ties in order to borrow money.
Uh oh....don't let the Arabs know when they shake hands with a Jew ....it could be their cousin! :o
George W. Bush will be reelected by a margin of at least ten per cent