September 30, 2004

PAGING BISHOP USSHER, YOUR APOLOGY IS READY (via Robert Schwartz):

Human populations are tightly interwoven: Family tree shows our common ancestor lived just 3,500 years ago. (Michael Hopkin, 29 September 2004, Nature)

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 Nature.


Presumably science will eventually figure out something that wasn't known by our ancestors millennia ago, but don't hold your breath. All the really big "breakthroughs" eventually end up back where we started--from the Big Bang, to Creation, to Geocentrism.

Posted by Orrin Judd at September 30, 2004 1:47 PM
Comments

Might a "randomly mating population"
be what we call a "race"?

Posted by: J.H. at September 30, 2004 1:51 PM

No its a bunch of horny guys in a waterfront bar.

Posted by: Robert Schwartz at September 30, 2004 1:59 PM

A helpful discussion of the article here:

http://www.corante.com/loom/archives/020118.html

Posted by: carter at September 30, 2004 2:19 PM

Sure, if you leave out the Indians who arrived in America 10,000 years ago, or the Australian Aborigines, who left Asia much earlier.

This is patently absurd on it's face, we have written history that goes back farther than that. The Egyptian empire was 1500 years old by this time. Are you going to tell me that the separate peoples who built civilizations in Egypt, Crete, Mesopotamia, the Indus Valley and China prior to 1500 BC were somehow wiped out, and new races born of this common ancestor spread out to all corners of the earth, developed their unique racial characteristics, and took over these civilizations without missing a beat?

Posted by: Robert Duquette at September 30, 2004 2:43 PM

Robert, methinks you misunderstand the premise of the article.

Posted by: Timothy at September 30, 2004 2:50 PM

From the article

"Researchers have calculated that the mystery person, from whom everyone alive today is directly descended, probably lived around 1,500 BC in eastern Asia."

Timothy, I thought I knew what "descended" meant and therefore I think Robert's statement was on point. What am I misunderstanding?

Posted by: h-man at September 30, 2004 3:41 PM

Robert, Orrin and h-man are confusing 'last common ancestor' with 'remotest ancestor'

When the geneaologists discover, as they always do, that both the American presidential candidates have a common ancestor in the English royal family, that does not mean that no one lived in England before the time of Henry VII.

It means, as the report says, that we are interlocked.

Think of it this way: the number of your direct ancestors doubles with each generation you go back.

Take 25 years as the length of a generation.
Go back 1,500 years. In that generation, you had more direct ancestors than there were people on Earth.

Go back another 100 years. In that generation, you had more than 16 times as many direct ancestors as there were people on Earth.

Obviously, there is a lot of double-counting and crossing.


Posted by: Harry Eagar at September 30, 2004 4:11 PM

I missunderstood nothing. BTW, OJ the Bishop got the date wrong its 5765, not 6008.

Posted by: Robert Schwartz at September 30, 2004 4:16 PM

Geocentrism? Holy smokes.

Posted by: doug at September 30, 2004 4:24 PM

I meant Robert Duquette.

Maybe I can simplify this for the statistically inept.

You and your first cousin have a pair of 'last common ancestors' who were your grandparents on one side.

That does not mean that you did not have another set of grandparents or that you did not have any great-grandparents.

Posted by: Harry Eagar at September 30, 2004 5:14 PM

Harry:

OK, I'll bite, but remember I was an Arts man. If Uncle Ling is the common ancestor of everyone alive today, why isn't his father?

Posted by: Peter B at September 30, 2004 7:04 PM

He is, but he would be the next-to-last common ancestor, not the last common ancestor.

If you marry into a Chinese family, your children will acquire a whole bunch of ancestors who -- we might have thought earlier -- had no connection to your Canadian set.

If this research is right -- and it looks OK -- it turns out your Canadian ancestors were already part-Chinese, and by marrying a Chinese woman, your children did not really acquire a new set, at least among the remoter generations.

It was previously estimated that the last common human ancestor was about 50,000 years ago, based on genetic drift.

The two estimates are not incompatible. A more recent last common ancestor would not have made much difference in gene frequencies yet. (We're talking about Y chromosome differences.)

I have not seen a discussion of this by a qualified person, but I suppose that we would now have to say that the 50,000-year-ago common (but not last common) ancestor represented a bottleneck.

In other words, at that time, humans were not global but few and local, and some selective event (somewhere near Ethiopia) pared the gene variation way down.

Not down to just one person, or one couple, but way, way down, the way it happened with the northern elephant seal recently (they have zero genetic diversity).

Of that small population, some number X continued to breed and spread, but from time to time, a branch would fail, like the Valois princes, until by now everybody traces back to just one coupling.

One or the other of us retains some of the genes of those failed lines, but what we're looking for in a last common ancestor is the point where every descendant traces back to that line.

Posted by: Harry Eagar at September 30, 2004 8:09 PM

As far as I can tell this study is based entirely on computer models of how populations might intermingle, and not at all on any sort of genetic basis. While their result seems almost certain to be true for Europeans, and plausibly for much of Asia, I'm doubtful about sub-Saharan Africa and don't believe it for a second for Indians from N. America (C. and S. America has seen much more interbreeding) or Australian Aborigines, as noted by Mr. Duquette, or probably Polynesians, or perhaps Japanese, etc. And please don't try to claim that I know nothing about statistics, because such is certainly not the case.

A much funnier article from the same Nature issue is this one: http://www.nature.com/news/2004/040927/full/040927-9.html, which shows quite well the perils of extrapolation...

Posted by: brian at September 30, 2004 8:47 PM

Harry:

A) Unlike with other arcane, silly subjects, like the history of Western Civilization, this is one where I really look to you for knowledge and guidance;

B) I haven't the slightest clue about what you are saying.

Posted by: Peter B at September 30, 2004 8:51 PM

What they are implying is that in the 500 years since 1492 all Amerindians now have at least one recent European/Asian/African ancestor. Or that somehow there was enough intermingling of a few stray people who made it to the Americas in the previous 3000 years to spread their genes from the Dene to the Patagonians. Since the URL seems to have gone bad, I dan't tell if t he online article addresses the issue.

These statistics also imply that we are all inbred to some degree, but that's still no excuse for the British royal family, Harvard graduates or the states of Arkansas and West Virginia.

Posted by: Raoul Ortega at September 30, 2004 9:19 PM

Wasn't he an Archbishop?

Posted by: jim hamlen at October 1, 2004 12:29 PM

Maybe it would make more sense, Peter, to think of it from the other direction.

The concept of 'last common ancestor' is crucial in evolution, but there can be at least two kinds.

Every organism had a last common ancestor that was some kind of protist 3.8 billion years ago, which had descendants that, one on path, became oak trees, and, on another, funguses.

The fungus path then branched to leave funguses and us. (This is not absolutely certain but is thought to be the original branching pattern.

Usually, when evolutionists speak of 'last common ancestor,' they mean the parent species just before a speciation event.

In a speciation, the parent continues, but a new, daughter species branches off.

This is irreversible.

In the case of humans, all one species, 'last common ancestor' is a slightly different concept.

Because the genes can recombine through mating, a branch that separated, say, 10,000 years ago (Polynesians) can be brought back in by the mere mating of a Polynesian with a European.

In an interview on NPR, somebody (didn't catch who he was, but I think one of the authors of the study) said that they tried to think of a human group that really was separate.

The closest they came was the Tasmanians, who seem to have no contact with the Australians, or anybody else, for many thousand years.

At contact, in the 18th century, the Tasmanians might not have had a 'last common ancestor' with other human groups more recent than a few tens of thousands of years ago.

But there are no pure-blooded Tasmanians left, all have some European ancestors, and hence acquired all the contacts that the rest of us have.

I was somewhat surprised no one presented it in the context of 'Six Degrees of Separation.'

David Hackett Fischer, in 'Albion's Seed,' has some good chapters on the mushroom effect of small populations moving into open spaces. Practically everybody in the Middle States shares ancestry with just a handful of English settlers in Delaware-New Jersey, even if only a smidgen.

Fischer, a historian, did not use genetic analysis but surnames.

Posted by: Harry Eagar at October 1, 2004 2:39 PM

Why are the results of a simulation taken as though they were fact? This is no more reliable than global warming simulations.

Posted by: Joseph Hertzlinger at October 3, 2004 1:33 AM
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