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."
Not at all necesarily true. Among my family, in my generation, two out of three siblings have no children. In my parent's generation, (father's side) one out of two have no children; mother's side, also one out of two have no children. So right now, my four grandparents have a combined total of ONE great-grandchild between them (and probably won't have any more, either.) That's three generations removed. If that kid becomes a priest, or dies young, all four grandparents will be out of the descendents game entirely.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 kind of thing happens a lot, especially in societies with high infant mortality. Which means most of the human race throughout most of its history.
Living in an age of population explosion, it's hard to recall that for most of human history, the population was fairly stable. This means that populations were not doubling every generation, they were about the same every generation. In other words the average couple produced and average of two descendants. For every couple that produced four (and this was a sizable fraction of the population) there was another couple that produced none (also a sizable fraction of the population).
Unless a newcoming interloper's genes are better fit (in Darwinian terms) than those of the native population, there is simply no way to be sure that his descendents (if any) will not die out in a few generations or less.
Living in an age of population explosion, it's hard to recall that for most of human history, the population was fairly stable. This means that populations were not doubling every generation, they were about the same every generation. In other words the average couple produced and average of two descendants. For every couple that produced four (and this was a sizable fraction of the population) there was another couple that produced none (also a sizable fraction of the population).
Unless a newcoming interloper's genes are better fit (in Darwinian terms) than those of the native population, there is simply no way to be sure that his descendents (if any) will not die out in a few generations or less.
You've nailed it. All over the world people have this congenital believe about 'blood and soil'-- that 'this land is for our people and not for inferior people'. They'll say that anyone who suggest that our ancestry does not extend back to the Beginning is not normal.
They're right-- I used the word "congenital" because I think these beliefs are actually hard wired into us at birth. Overcoming these prejudices may be a big step toward reality, but it's just not normal. The irony is the very fact that this common belief is so universal is even more proof of recent ancestry.
well, most of us ARE cousins to everyone else -- the degree of relationship will vary (100th cousin anyone!?)
WEll, that is an extreme example -- however, most of the peoples populating the Eurasian continent and Africa north of the Sahara have had regular contacts for millenia. The more apparent are the Caucasians -- you can most definitely say that if you have any amount of Caucasian blood, you are related to those who faced CAesar's troops in 54 B.C. and those who created the VEdas in the second millenia and those who built the pyramids and those who trudged with Moses.
There are extremes such as the MElanesian tribes in Papua New Guinea (Australoids I think and related to the Australian Aborigines) or a remote South American tribe or the Bushmen. Most other groups are not that isolated
#21, #22, well put (again).
bttt, and a related topic:
Maori Men And Women From Different Homelands
ABC Science News ^ | 3-27-2003 | Adele Whyte
Posted on 09/06/2004 5:15:41 PM PDT by blam
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If you ignore the evidence, and follow your imagination, anything is possible.
Aborigines in Australia, Pigmies deep in the jungles of Africa, Indians in the Americas, Blonds in Europe, and black haired Asians of which all have traits peculiar to their ethnicity and uncommon to all need a vast amount of time to acquire these isolated differences. It did not happen a few thousand years ago.
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