Posted on 01/28/2003 8:46:54 PM PST by CalConservative
| The Death of "Mitochondrial Eve" By: Brad Harrub, Ph.D.* It was not forbidden fruit that caused her demise this time. “Mitochondrial Eve,” as many knew her, has been dethroned and awaits her entombment due to new facts that have recently surfaced. For decades now men have been trying to determine the geographical origin of humans: whether we all came from one specific locale, or whether there were many small pockets of people placed all around the world. It appeared that the battle was won in the late 1980s when geneticists unleashed a startling discovery. They found that DNA located in the nucleus of a cell was different from the DNA found outside the nucleus, in organelles called mitochondria. Realizing that the DNA in mitochondria was not a product of procreation, and knowing that eggs destroy sperm following fertilization, scientists speculated that mitochondrial traits, including a variety of inherited disorders, were exclusively passed down from the mother. This discovery brought with it another revelation. If humans received mitochondrial DNA (mtDNA) from only their mothers, then researchers could “map” a family tree using that information. Thus, a hypothesis was formed that included a “molecular clock” of evolution, which emerged from early observations that DNA tended to mutate linearly with time. If indeed, mtDNA evolved at constant rates, then it could serve as a molecular clock for timing evolutionary events and reconstructing the evolutionary history of extant species. Given enough information, scientists believed they could accurately show where humans had originated--thus “mitochondrial Eve.” A recent 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. On page 2524 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. 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 (Strauss, 1999, p. 2436). 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…. If mtDNA can recombine, irrespective of the mechanism, there are important implications for mtDNA evolution and for phylogenetic studies that use mtDNA (Morris and Mightowlers, 2000, p. 1290, emp. added). Just this past year a study was conducted that stirred these words: “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…. The unusual case described by Schwartz and Vissing is more than a mere curiosity” (Williams, 2002, p. 611, emp. added). And now we know that these are more than small “fractional” amounts of mtDNA coming from fathers. The New England Journal of Medicine recently noted one study in which, “[w]e determined that the mtDNA harboring the mutation was paternal in origin and accounted for 90 percent of the patient’s muscle mtDNA” (Schwartz and Vissing, 2002, p. 576). Ninety percent! And all this time we have been selectively shaping our family tree using only mothers?! As scientists begin to comprehend the finality of mitochondrial Eve, many have found themselves searching for alternatives that can maintain their beliefs on 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. But “with recombination there is no single tree,” notes Harpending. Instead, different parts of the molecule have different histories. Thus, “there’s not one woman to whom we can trace our mitochondria,” says Eyre-Walker (Strauss, 1999, p. 2436). Goodbye Eve. References:
* Dr. Brad Harrub serves as Director of Scientific Information, Apologetics Press. (Brad@apologeticspress.org) |
I'm telling ya, people shock as to what they are willing to have fantasies on when it eliminated the Judeo Christian God. The truth is God created us all and we are all decendents of Adam and Eve.
Probably still sulking about the Raiders losing the Super Bowl. I kinda figure that they are all Raiders fans and such - survival of the fittest and all that...
Also we all decended from Noah . . .
I'm right here, why?
No comment from the peanut gallery tonight?
What would you like to know? While it's disappointing that the mitochondrial DNA evidence can't be "read" as cleanly as hoped, it still contains a wealth of information that can be used to track lineages, just like nuclear DNA. And even though paternal mtDNA can be passed, the mechanism is different enough from the way that nDNA is inherited that the two types of DNA can still be used as independent "cross-checks" of the implications made by each other.
Furthermore, tracing mtDNA lineages now becomes a bit more complicated, since parental lineages have to be considered as well as just maternal, but otherwise the analysis is mostly unchanged -- it *is* still inherited, and who shares which variations is still a very rich field for study, which will continue to yield a wealth of information.
The loss of "Eve" isn't a big blow, it was more "valuable" as a PR tool (the media and public found it more fascinating than the usual sort of findings) than as an actual research finding.
Geesh, here I thought they really knew their stuff (LOL).
They do. And note that it was further research into genetics and evolution which produced the realization that new mtDNA transfer methods needed to be taken into account. Science marches onward, learning ever more as it goes and refining its findings.
Furthermore, I don't recall any creationists ever sagely pointing out, "I say good fellow, it says here in Genesis that paternal mtDNA is not always eliminated."
To all -- please ping me to other topics which are appropriate for the GGG list. Thanks.Fathers can be influential tooBiologists have warned for some years that paternal mitochondria do penetrate the human egg and survive for several hours... Erika Hagelberg from the University of Cambridge, UK, and colleagues... were carrying out a study of mitochondrial DNAs from hundreds of people from Papua-New Guinea and the Melanesian islands in order to study the history of human migration into this region of the western Pacific... People from all three mitochondrial groups live on Nguna. And, in all three groups, Hagelberg's group found the same mutation, a mutation previously seen only in an individual from northern Europe, and nowhere else in Melanesia, or for that matter anywhere else in the world... Adam Eyre-Walker, Noel Smith and John Maynard Smith from the University of Sussex, Brighton, UK confirm this view with a mathematical analysis of the occurrence of the so-called 'homoplasies' that appear in human mitochondrial DNA... reanalysis of a selection of European and African mitochondrial DNA sequences by the Sussex researchers suggests that recombination is a far more likely cause of the homoplasies, as they find no evidence that these sites are particularly variable over all lineages.
by Eleanor Lawrence
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