Philip Awadalla, 1 Adam Eyre-Walker, 2* John Maynard Smith 2, "Linkage
Disequilibrium and Recombination in
Hominid Mitochondrial DNA ", Volume 286, Number 5449 Issue of 24 Dec 1999,
pp. 2524 - 2525
I have yet to see it but the press accounts are interesting.
http://www.abcnews.go.com/sections/science/DailyNews/dna_evolution991223.html
declining linkage disequilibrium as a function of distance. They say that
this is due to recombination of maternal and paternal mitochondrial DNA in
the egg. If this is so, then the coalescence age of the mtDNA is NOT
100,000- 200,000 years, but 200-400 thousand years which is a time long
before anatomically modern men were on the earth.
Christian apologists simply can not ignore this paternal inheritance of
mtDNA in order to exclude earlier hominids from our family. Given the
numerous documentations of human behavior among the hominids that I have
posted and written about in my PSCF articles and in Adam,Apes and
Anthropology, it seems futile to try to rescue Christian apologetics by
depending upon the broken reed of mtDNA.
Concerning the earlier blows to clonal inheritance of mtDNA this year I
want to reproduce the message I sent out in April concerning these other
two articles.
**begin**
Mitochondrial Eve
In March there were reports of two studies which showed that
paternal inheritance, and maternal/paternal mtDNA
recombination took place. These studies show that mtDNA is
NOT solely inherited from the mother as all mtDNA studies to
date assume. I finally obtained those two articles. They do
indeed have profound implications for the way Christians
handle fossil man. These articles falsify the view that
mankind is a recent (circa 100,000 year) addition to our
planet. They also falsify the notion that Neanderthal is a
separate species which was the conclusion drawn by many
after the first mtDNA study of Neanderthal (Krings, 1996),
The first is Hagelberg et al, (1999). The second is Eyre-
Walker et al, (1999) [references below].
The Hagelberg study examined the mtDNA population structure
in Melanesia. They compared the mtDNA from 452 individuals
finding three major mtDNA lineages implying three different
migrations of peoples into the Pacific basin. Since the time
of the peopling of the Pacific, these three lineages had
mutated into at least 175 different haplotypes of mtDNA.
But they found the same mutation at one DNA site on 8 different
haplotypes which represent all three mtDNA lineages. This
mutation is unique to the people of the island of Nguna.
Nguna is inhabited by about 1000 people so to find the same
mutation in three different supposedly matrilineages is
surprising. I will quote at length their discussion.
There is strong statistical support for the existence
of three separate human mtDNA lineages in our data.
Interestingly, we detected a base substitution at mtDNA
position 16076 in people belonging to eight separate mtDNA
types falling into the three separate Pacific lineages in
the small island of Nguna. The presence of a rare mutation
in people of different lineages is puzzling. There can be
several explanations for this observation:The 16076
mutations occurred several times by cahnce in the island of
Nguna if position 16076 was hypervariable. Alternatively,
the 16076 substitution might have occurred just once before
the split of the three separate lineages, although this
would mean that several subsequent reverse mutations at
other sites must have happened to account for the data
observed. A third explanation is that the 16076 mutation
occurred once in an ancestor of the present Nguna population
and was subsequently transferred to other lineages by
paternal leakage of mtDNA and subsequent recombination.
Hypervariability in mtDNA is a well-recognized
phenomenon. IN current human mtDNA studies , the multiple
occurrence of base substitutions in separate branches of a
phylogenetic tree is generally attributed to independent
mutations at hypervariable sites of the mtDNA control
region. According to this view, the 16076 mutation would
have had to have occurred independently several times in
Nguna, but virtually nowhere else in the world populations
studied to dae, and in none of the other locations of our
study. This seems unlikely. It is also unlikely that the
160076 mutation happened before the three lineages diverged,
as this would mean that several back-=mutations would have
had to occur at this site to explain the existence of the
other mtDNA types without this substitution in Nguna and
throughout the western Pacific.
Although at odds with current dogma on mtDNA
inheritance, paternal contribution and genetic recombination
are possible explanations for the phenomenon observed in
Nguna. Views on the strict maternal inheritance of mtDNA
have been challenged. Paternal inheritance of mtDNA was
observed in mice progeny at a frequency of one in 10000. IN
contrast to popular belief, the sperm tail with its
mitochondria is not excluded from the embryo during human
fertilization (Ankel-Simons & Cummins 1996[Ankel-Simons is
Gordon Simons cousin in law--grm]), although experimental
evidence for an active exclusion mechanism ahs been
presented. If such a mechanism exists, it has the potential
to fail on occasions, which would enhance the rates of
paternal mtDNA leakage.
"It seems liekly that paternal mtDNA molecules might
make a small, albeit significant, contribution to mtDNA
lineages, particularly if measured over prolonged time
periods of evolutionary history." ( Hagelberg et al, 1999, p
489-490)
They go on to state,
"If our conclusion is correct, genetic recombination
probably occurred at least twice (and possibly as many as
eight times) in Nguna and it therefore a relatively frequent
event in human evolution. This has important implications
for evolutionary and phylogenetic studies of human mtDNA.
First, recombinations would perturb estimates of the time of
divergence of mtDNA types, raising questions about the
suggested time and mode of recent human evolution. Second,
the occurrence of recombination would cast doubts on the
labelling of some mtDNA control region nucleotide positions
as mutation hotspots. It is just as likely that the
frequent occurrence of some substitutions in unrelated human
lineages might be the result of recombination, notably in
populations like those of Europe which have undergone high
levels of genetic admixture in recent millenia.
"In our data on Pacific populations, we detect little
evidence for the existence of hypervariable sites that could
not be explained by the occurrence of recombination events.
For example, position 16129 is considered to be one of the
most hypervariable in human mtDNA, with a rate approximately
eight times higher than the background mutation rate in the
first hypervariable segment of the human mtDNA control
region.. . . If position 16129 was hypervariable, it is
extraoridinary that it has not changed in the western
Pacific in the long time since the expansion of people into
New Guinea and island Melanesia, a period of 30 000 to 60
000 years. How likely is it for position 16129 to be fixed
in the Pacific but hypervariable in the rest of the world?
. . .
"We would like to suggest that some of the so-called
hypervariable sites, for example 16129, 16223, 16311 and
16362, are in fact extremely ancient substitutions in human
mtDNA, which accounts for their widespread distribution in
human populations. The occurrence of these substitutions in
different mtDNA lineages, used as evidence of their
hypervariability, could simply be the result of their
extreme antiquity, couples with the effects of occasional
recombination events. It is interesting that the
distribuiton of these substitutions is particularly high in
African populations, as well as in New Guinea highalnnders,
who are thought to descend from some of the earliest
anatomically modern humans to migrate out of Africa."
(Hagelberg et al, 1999, p.490-491
The African population is the oldest population of humans on
Earth.
Hagelberg et al then address why human mtDNA has so little
variance when compared with the variance seen in other
species like chimpanzees.
"One of the worldwide effects of recombination would be
to blur the differences between human mtDNA lineages, as
recombination would create hybrid haplotypes and eradicate
ancient haplotypes. This would make it harder to
reconstruct the ancestral relationships of human
populations. If paternal mtDNA leakage and subsequent
recombination or some analogous gene conversion event are
significant in human evolution, it will be necessary to
revise the conclusions of many current studies based on
mtDNA, including views on the relationship between
Neanderthals and modern humans. The occurrence of a mtDNA
type which differs at 27 positions from an average modern
human mtDNA sequence would not be sufficient to conclude
that a single Neanderthal individual was of a species that
did not interbreed with anatomically modern humans, as a
lineage of such antiquity could easily be lost in the
intervening 30 000 or more years since the individual
lived." (Hagelberg et al 1999, p. 491)
The other study, by Eyre-Walker et al, is a statistical
study of variations in mtDNA among chimps, gorillas and
humans. Basically this study showed that there are too
many back-mutations (Homoplasies)to be accounted for by
matrilineally inherited mtDNA. They studied the third site
in nucleotide codons. The third site is the third nucleotide
in the coding which occurs for proteins. They state,
"An analysis of 3628 synonymous third sites in the
protein-coding regions of 29 human mitochondrial sequences
revelaed 126 polymorphisms. If all third sites were equally
liekly to change, the expected number of Homoplasies would
be 2.2, whereas the observed number is 22; the probability
of such an excess is effectively zero. It follows that there
there has either been recombination or that all third sites
are not equally likely to change." (Eyre-Walker et al, 1999,
p. 481)
The idea that mutation probabilities are not equal is
addressed by Eyre-Walker, as it was in Hagelberg et al's
paper. Eyre-Walker et al state,
"There is no evidence of variation in the mutation
rate. If some sites have an elevated mutation rate in both
directions, this would cause sites that are variable in
humans to also be variable in other primates. In fact, no
such tendency exists. The humber of polymorphic sites and
of apparently Homoplastic sites in humans that are variable
in other primates both agree rather closely with the numbers
expected if all third sites are equally likely to change.
(Eyre-Walker et al, 1999, p. 481)
Eyre-Waler et al (p. 481) then argue that recombination is a
real phenomenon,
"Finally, two steps which are required for
recombination between mitochondrial lineages are known to
exist. Paternal mitochondria enter the egg (Kaneda et al,
1995; Ankel-Simmons & Cummins 1996) and they contain the
enzymes necessary for Homologous recombination (Thyagarajan
et al, 1996). The only barriers to recombination are the
fusion of mitochondria and the time for which paternal
mitochondria survive once they are in the egg. It remains
cunclear whether mitochondria fuse frequently and in mice
there are efficient mechanisms for eliminate paternal
mitochondria, so that, within several hours of
fertilization, paternal mtDNA can no longer be detected.
However, only relatively low levels of recombination are
probably required to generate the patterns of Homoplasy we
observe."
They conclude,
"Mitochondrial DNA has been used extensively in the
study of human evolution. In many of these analyses the
clonality of mitochondria has been either explicitly or
implicitly assumed. It is clear that many of these
conclusion will have to be treated with caution or
reassessed. It certainly seems dangerous to assume that
mitochondria are clonal when there is evidence against and
no evidence in favour of such a conjecture." (Eyre-Walker et
al, 1999, p. 482.
This data, along with the possible Neanderthal/Human hybrid
reported earlier, screams out for a new apologetical
treatment. Christians who have argued for a humanity that
was less than 100,000 years old and genetically separate
from archaic Homo sapiens such as Neanderthal and Homo
erectus are in danger of following the path traveled by the
young-earth creationists. That is, they are beginning to
ignore important pieces of data in order to support their
preferred theological interpretation. This is a too often
occurrence among many christian apologists.
References
Eyre-Walkeer, Noel H. Smith and John Maynard Smith, "How
Clonal are Human Mitochondria?", Proc. Royal Soc. Lond. B
(1999) 266:477-483
E. Hagelberg et al, "Evidence for Mitochondrial DNA
Rcombination in a Human Population of Island Mwelanesia,"
Proc. Royal Soc. Lond. B (1999) 266:485-492
Matthias Krings, et al., "Neandertal DNA Sequences and the
Origin of Modern Humans," Cell, 90:19-30
glenn
Foundation, Fall and Flood
Adam, Apes and Anthropology
http://www.flash.net/~mortongr/dmd.htm
Lots of information on creation/evolution