RE: So we're all related!

Vernon writes:

-----Original Message-----
From: asa-owner@lists.calvin.edu [mailto:asa-owner@lists.calvin.edu]On
Behalf Of Vernon Jenkins
Sent: Saturday, October 02, 2004 9:49 PM

To the Forum

An interesting article appeared in last Thursday's Daily Telegraph which may
be found at
http://news.telegraph.co.uk/news/main.jhtml?xml=/news/2004/09/30/wdesc30.xml
It briefly describes the outcome of a programme of research carried out at
MIT by a team led by Dr Steve Olson - this suggesting that all people alive
today share a single common ancestor who lived in Asia in 1,415 BC. [Dr
Olson was keen to stress however that this date was an estimate.]
If indeed true, then this finding suggests that - apart from a handful of
fortunate individuals - mankind was completely snuffed out not that long
ago. Had Dr Olson's estimate been 880 or so years earlier then, clearly, the
Genesis Flood - provided it were accepted as a _global_ cataclysm - would
have provided the necessary mechanism for such mass extinction. But if not a
universal flood, then what? Perhaps the estimate is wrong; perhaps the
procedure which has led Dr Olson to conclude that all - since 1,415 BC - are
descended from a single ancestor, is wrong. It is all highly intriguing. I
invite informed comment from the list.
********

The original article is in Nature. I have put together a couple of
articles I posted on another site about this article.

This article has nothing to say about a single ancestor from that time
period. There are 150 generations between us and those alive 3000 years ago.
With each generation back there are twice as many ancestors. We have 2
parents, 4 grandparents, 8 great grandparents, etc. Since 3000/20 =150, we
have 2^150 = 1.45 x 10^45 slots in our ancestry. What this means, is that
the same person occupies billions of these slots in our ancestry.

The article was merely a statistical study on how likely it is that one
person occupies at least one slot in all the genealogies of the 6 billion
people alive today. Given that there were around 100 million people alive
3000 years ago (this estimate can be extrapolated from L. Luca
Cavalli-Sforza, Paoli Menozzi and Alberto Piazzi, The History and Geography
of Human Genes, (Princeton: Princeton University Press, 1994), p. 68)

this means that each person 3000 years ago occupies an average of 1.45 x
10^37 slots out of our 1.45 x 10^45 slots.

Now, one should know, that just because we are all descended from some
individual 3000 years ago it doesn't mean that we all inherited genes from
that person. There is only a 10^-37 probability that all of us have any
genes from this guy or gal.

So in short, this person is neither Adam nor Eve, nor Noah and his wife.

This is the problem with the article. They explicitly say that they

 Quote Taken From:
 Rohde et al, "Modeling the recent common ancestry of all living humans,"
Nature, Sept 30, 2004, p. 562

>For a population of size n, assuming random mating (and so
>ignoring population substructure), probabilistic analysis has
>proved that the number of generations back to the MRCA, Tn,
>has a distribution that is sharply concentrated around log2n.

Now, a guy on that other list pointed out that population substructure
actually falsifies the common ancestor applying to the Tasmanians. It
probably also doesn't apply to the Native Americans since they too were
isolated from the Old World from around 12,000 years ago until 1492 AD. So
the guys in the article calculated a simplistic model (which raises the
question of what is so earthshattering about this model as to warrent
publication in Nature). They say:

 Quote Taken From:
 Rohde et al, "Modeling the recent common ancestry of all living humans,"
Nature, Sept 30, 2004, p. 565
>With 5% of individuals migrating out of their home town, 0.05%
>migrating out of their home country, and 95% of port users born in
>the country fromwhich the port emanates, the simulations produce
>a mean MRCA date of 1,415 BC and a mean IA date of 5,353 BC.
>places. Studies of hunter-gatherer groups and subsistence agricultural
>communities have found that anywhere from 1% (ref. 19) to as
>much as 30% (ref. 20) of mates are from outside the group.

But that can't apply very well to Tasmania or even Keppel Island off of
Australia's coast as well. Thus the model really doesn't match real world
realities.
Received on Sat Oct 2 18:40:40 2004