Continuing from the last post, it
was not forbidden fruit in the Garden of Eden that caused mitochondrial Eve’s
demise this time around. The “passing” of one of evolution’s most
familiar icons is due to new scientific facts that have surfaced since her
introduction in 1987. If humans received mitochondrial DNA only
from their mothers, then researchers could “map” a family tree using that
information. And, if the mutations affecting MtDNA had indeed
occurred at constant rates, then the MtDNA could serve as a molecular clock for
timing evolutionary events and reconstructing the evolutionary history of
extant species. It is the “if"s in these two sentences that are the
problem.
Researchers say that Eve was sturdy and
fruitful and problem lived in a small group that scoured the plains for food,
though they cannot decide whether it was Asia or Africa
Mitochondrial Eve is alleged to
have lived in Africa at the beginning of the Upper Pleistocene period (between
100,000 and 200,000 years ago). She has been described as the most-recent
common ancestor of all humans on Earth today, with respect to matrilineal descent.
The validity of these assertions, however, is dependent upon two critically
important assumptions: (1) that MtDNA is, in fact, derived exclusively from the
mother; and (2) that the mutation rates associated with MtDNA have remained
constant over time. However, we now know that both of these assumptions are
wrong!
First, let us examine the assumption that MtDNA is derived
solely from the mother. In response to a paper that appeared in Science in 1999, anthropologist Henry B.
Eyring of the University of Utah lamented: “There is a cottage industry of
making gene trees in anthropology and then interpreting them. This paper
will invalidate most of that” (as quoted in Evelyn Strauss, “MtDNA Shows Signs
of Paternal Influence,” Science, Vol
286, p2436, 1999). Just as women thought they were getting their fair
shake in science, the tables turned. As one study noted:
"Women have struggled
to gain equality in society, but biologists have long thought that females
wield absolute power in a sphere far from the public eye: in the mitochondria,
cellular organelles whose DNA is thought to pass intact from mother to child
with no paternal influence." However, a study by Philip Awadalla of the
University of Edinburgh and Adam Eyre-Walker and John Maynard Smith of the
University of Sussex in Brighton, U.K. finds signs of mixing between
maternal and paternal mitochondrial DNA (MtDNA) in humans and chimpanzees.
As Strauss stated: “Because biologists
have used MtDNA as a tool to trace human ancestry and relationships, the
finding has implications for everything from the identification of bodies to
the existence of a “mitochondrial Eve” 200,000 years ago.”
Geneticists claim that DNA can be a valuable
tool when doing genealogical research on a family and that tests can indicate
clan relationships and connect a family tree back to a distant ancestor
One year later, however, researchers made this startling
admission:
Mitochondrial DNA (MtDNA)
is generally assumed to be inherited exclusively from the mother. Several
recent papers, however, have suggested that elements of MtDNA may sometimes be
inherited from the father. This hypothesis is based on evidence that MtDNA may undergo recombination. If this does occur, maternal MtDNA in
the egg must cross over with homologous sequences in a different DNA molecule;
paternal MtDNA seems the most likely candidate. Morris and Mightowlers
added, “If MtDNA can recombine,
irrespective of the mechanism, there are important implications for MtDNA
evolution and for phylogenetic studies that use MtDNA.”
In 2002, a new study was conducted by Schwartz and Vissings that
concluded: “Nevertheless, even a single validated
example of paternal MtDNA transmission suggests that the interpretation of
inheritance patterns in other kindreds thought to have mitochondrial disease
should not be based on the dogmatic assumption of absolute maternal inheritance
of MtDNA.” Williams added that this case study “Is more than a mere
curiosity.”
And now we know that these are more than small “fractional”
amounts of MtDNA coming from fathers. The August 2002 issue of the New England Journal of Medicine
contained the results of the Swartz and Vissing study, which concluded:
“Mammalian
mitochondrial DNA (MtDNA) is thought to be strictly maternally inherited. Very
small amounts of paternally inherited MtDNA have been detected by the
polymerase chain reaction (PCR) in mice after several generations of interspecific
backcrosses. We report the case of a 28-year-old man with mitochondrial
myopathy due to a novel 2-bp MtDNA deletion. We determined that the MtDNA
harboring the mutation was paternal in origin and accounted for 90-percent of
the patient’s muscle MtDNA. Ninety
percent! And all this time, evolutionists have been selectively shaping
our family tree using what was alleged to be only maternal MtDNA!
As scientists have begun to comprehend the fact, and
significance, of the “death” of mitochondrial Eve, many have found themselves
searching for alternatives that can help them maintain their current beliefs
regarding human origins. But this recombination ability in MtDNA makes
the entire discussion a moot point. As Strauss noted: “Such
recombination could be a blow for researchers who have used MtDNA to trace
human evolutionary history and migrations. They have assumed that the MtDNA descends only through the mother, so they could draw a single
evolutionary tree of maternal descent—all the way back to an African
“mitochondrial Eve,” for example. And Harpending added, “with
recombination there is no single tree.” In addition, Eyre-Walked says.“ Instead,
it has been found that different parts of the molecule have different histories,
and as Eyre-Walker concluded, “there’s
not one woman to whom we can trace our mitochondria.”
In fact, we couldn’t agree more.
Secondly, the
assumption that the mutations affecting
mtDNA did indeed occur at constant
rates, and that researchers who made the initial announcement about Eve not
only gave a location for this amazing female, but also proposed the time period
during which she was supposed to have lived. However, in order for the
mtDNA theory to be of any practical use, those scientists had to assume that
random mutations in the DNA occurred at documented, steady rates. As
stated in the last post, if the speculation was one mutation every 1,000 years,
and they found a difference of 10 mutations between us and our ancient
hypothetical ancestor, they then could infer that that ancestor lived 10,000
years ago. Scientists who used this concept to determine the age of
mitochondrial Eve referred to this proposed mutation rate as a “molecular
clock.” One group of researchers, headed by Rodriguez-Trelles, described the
process as follows:
“The hypothesis of
the molecular clock of evolution emerged from early observations that the
number of amino acid replacements in a given protein appeared to change
linearly with time. Indeed, if proteins (and genes) evolve at constant
rates they could serve as molecular clocks for timing evolutionary events and
reconstructing the evolutionary history of extant species.” And, of course, it sounded good in theory, but
the actual facts tell an entirely different story. As these same
researchers went on to admit:
“The neutrality
theory predicts that the rate of neutral molecular evolution is constant over
time, and thus that there is a molecular clock for timing evolutionary
events. It has been observed that the
variance of the rate of evolution is generally larger than expected
according to the neutrality theory, which
has raised the question of how reliable the molecular clock is or, indeed,
whether there is a molecular clock at all. The observations are
inconsistent with the predictions made by various subsidiary hypotheses
proposed to account for the overdispersion of the molecular clock.”
(See the next post, “A
Second, Closer Look at DNA – Part III – The Problems With DNA “Science” Part
II, The Demise of Mitochondrial Eve,” and further information on the problems
with previously thought female-only MtDNA)
What's wrong with saying: Here is what we have found so far, as opposed to: this is how it is? Why do the people whom we trust to inform us feel a need to teach us WHAT to think instead of HOW to think?
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