>-----Original Message-----
>From: asa-owner@lists.calvin.edu [mailto:asa-owner@lists.calvin.edu]On
>Behalf Of Walter Hicks
>Sent: Wednesday, April 24, 2002 2:32 AM
>If every man in the world can trace his father's father's father back to
>this "Adam", then how can there be any different father back there. I
>know for a fact that only had one father and my sister only had one
>mother. Ah, you say, through the paternal grandfather for me and through
>maternal grandmother for sis. But that only works if the former had no
>male children and the later had no female children. Otherwise, they
>could back through the same chain to Adam/Eve.
>
>Where does all the cross breeding fit in?
>
>Something is eluding me. Can someone (say Glenn) help?
There are several terms one must know first. Coalescence time is the time
it takes for the genetic variability seen at a given gene to arise. We know
the mutation rate and can work backwards to figure out statistically how
long it would take for that much variability to arise. In the case of the Y
chromosome mtDNA upon which mtDNA Adam and Eve are based, the times are
somewhere in the 100,000 year range. Does this mean that all humans
descended from two people who lived in that time frame? no.
Crossover is the next term you need to be familiar with. This means that at
cell division parts of chromosomes can actually change chromosomes. Genes
that are on one copy of a nuclear chromosome can trade places with the
homologous gene on the other chromosome. THis means that the nuclear DNA is
kind of a mix-master set of instructions for you. This and the fact that
there are two copies of every nuclear gene means that as the nuclear DNA
mutates, it will take 4 to 9 times longer for nuclear DNA to coalesce than
for the non-crossing over Y chromosome or mtDNA. Thus, if it takes 100,000
years for mtDNA to generate the variability we see, it would take 400,000 to
900,000 years for the nuclear genome to collect the variability it has.
Finally, you need to know that every scrap of nuclear DNA has a different
last common ancestor. A last common ancestor is the person with the
genetic sequence who gave rise to all the variant forms we see on earth
today. So, while the last common ancestor of mtDNA is within the past few
thousand years, the last common ancestor for segment 541,476 of chromosome
12 may have lived 500,000 years ago, and the last common ancestor for
segment 541,477 may have lived only 200,000 years ago. (the segments are
illustrative only).
>From this, I know that if it takes 100,000 for mtDNA to coalesce, then it
will take 400 to 900 for nuclear genes to coalesce and that is exactly what
we see in genetics. There are several very old genetic systems being found
today in the nuclear genome. see
http://www.glenn.morton.btinternet.co.uk/hegene.htm
All the references are there.
>
>
>Oh, and how can we know that all of the billions on this earth have the
>same mtDNA and XY-DNA anyhow?
Statistically. Of course we can't examine all the people but if you sample x
number of people and don't find a new strain then statistically (like a
poll) you figure that the odds of finding that rare variant is quite small.
Therre has been one article of late which addresses this issue. Templeton
analyzed all the data and found that there were several out of Africa
expansions much older than the most recent 100,000 years ago expansion. He
notes that if there had been a total replacement of archaic peoples, the
evidence for ancient genes would have been wiped out. It wasn't. Templeton
writes:
ìThe highest clade level inferences for five genes are range expansions out
of Africa (mtDNA at 0.13 Myr ago; Y-DNA at 0.09 Myr ago; MC1R at 0.64 Myr
ago; and -globin at 0.82 Myr ago) and a range expansion of ambiguous origin
(MS205 at 0.63 Myr ago). Figure 3 shows that gamma distributions associated
with the ages of these expansion events. The -globin inference has 5.6% of
its probability mass at 1.7 Myr ago or older, but all the other inferred
range expansions have much less probability mass at 1.7 Myr ago or older.
Hence, there is no cross-validated inference of marking the original
expansion of Homo erectus out of Africa. Figure 3 shows that the five
inferences fall into two broadly overlapping classes; the mtDNA and Y-DNA
that are tightly clustered around an expansion event out of Africa at about
100,000 years ago, and the three autosomal loci with means between 0.64 to
0.82 Myr ago. To test the null hypothesis that all five loci are compatible
with a single range expansion event, the lower age bound was found such that
0.1% of the [beta]-globin probability distribution was above this age (this
locus has the oldest inferred expansion event) and the upper age bound was
found such that 0.1% of the Y-DNA probability distribution was below this
age (this locus has the youngest inferred expansion event). Any age outside
of this interval would be strongly rejected (at the 0.1% level) on ths basis
of Y-DNA or [beta]-globin alone. This interval spans between 0.0474 to
0.2906 Myr ago and is shown in grey in Fig. 3. The probability that all five
loci are detecting an event in this age interval is 0.003. Because the
expansion event detected with MS205 is of ambiguous geographical origin, the
calculation was repeated excluding that locus to focus specifically upon
out-of-Africa expansion events. With this exclusion, the hypothesis of a
single out-of-Africa expansion event is rejected with P = 0.018. The broad
overlap of the mtDNA and Y-DNA distributions (Fig. 3) indicates that the
null hypothesis of these two genetic elements marking the same out-of-Africa
range-expansion event cannot be rejected, and similarly the null hypothesis
that the three nuclear markers in Fig. 3 are marking the same expansion
event cannot be rejected. The parsimonious explanation of Fig. 3 is
therefore a minimum of two out-of-Africa expansion events, both of which are
cross-validated by more than one locus. Combining the three nuclear genes,
the 95% confidence interval for the older out-of-Africa range-expansion
event is 0.42 to 0.84 Myr ago. Combining the mtDNA and Y-DNA distributions,
the 95% confidence interval for the more recent out-of-Africa expansion
event is 0.08 to 0.15 Myr ago.
îThe GEODIS analyses indicate that the most recent out-of-Africa
expansion event was not a replacement event. If it had been, the three
significant genetic signatures of the older expansion event (Fig. 3) and the
six significant genetic signatures of older recurrent gene flow (Fig. 2)
would have been wiped away. Although there is considerable error in dating
any single inference from only one gene, an out-of-Africa replacement event
would require that all nine significant inferences found in all eight
bisexually inherited nuclear loci examined would have to be in error
simultaneously. Moreover, the dating errors would have to be large in all
nine cases and in the same direction. The hypothesis of a recent
out-of-Africa replacement event is therefore strongly rejected. Indeed, this
is the most highly cross-validated conclusion of the entire analysis because
every gene region that is expected to contain information about events or
processes substantially older than 0.15 Myr ago leads to a rejection of
recent replacement. Hence, this is a genome-wide conclusion and not a
locus-specific conclusion. The out-of-Africa expansion that took place
between 0.08 to 0.15 Myr ago therefore represented a major movement of
peoples characterized by interbreeding and not replacement.
î Alan Templeton, ìOut of Africa Again and Again,î Nature, 416(2002):45-51,
p. 48-49
This view could be called "mostly out of Africa a 100,000 years ago" view in
which most of our genetic heritage does come from this latest expansion but
not 100% of it.
glenn
see http://www.glenn.morton.btinternet.co.uk/dmd.htm
for lots of creation/evolution information
anthropology/geology/paleontology/theology\
personal stories of struggle
>
>Walt
>
>--
>===================================
>Walt Hicks <wallyshoes@mindspring.com>
>
>In any consistent theory, there must
>exist true but not provable statements.
>(Godel's Theorem)
>
>You can only find the truth with logic
>If you have already found the truth
>without it. (G.K. Chesterton)
>===================================
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