The Death of
"Mitochondrial Eve"

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.”

According to the information disseminated by scientists, mitochondrial Eve 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--a mathematical fact. However the facts behind Eve’s alleged homeland and pedigree have many mathematicians looking for the “clear” key on their calculators. For it turns out that this nice little theory has more holes than Wisconsin-aged Swiss cheese. The problem hinges on the fact that this entire premise is based on mtDNA coming exclusively from the mother---something we now know is not always the case.

A 1999 paper appeared in Science that had Henry Harpending, an anthropologist at the University of Utah lamenting: “There is a cottage industry of making gene trees in anthropology and then interpreting them. This paper will invalidate most of that” (Strauss, 1999, p. 2436).  And just at the point in which women thought they were getting their fair shake in science the tables turned.

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).
One year later 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….

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).
All of the inferences that have been drawn from this research must now be cast aside--for Eve is dead. Rather than reconsidering and revamping the theory, scientists must realize the truth and be ready to accept the ultimate demise of “mitochondrial Eve.” Science is a field that analyzes data and then forms hypothesis based on that information--not one that massages the data until it fits a certain hypothesis.

Goodbye Eve.

References:

• Morris, Andrew A. M., and Robert N. Lightowlers (2000), “Can Paternal mtDNA be Inherited?,” The Lancet, 355:1290-1291, April 15.
  Schwartz, Marianne and John Vissing (2002), “Paternal Inheritance of Mitochondrial DNA,” New England Journal of Medicine, 347[8]:576-580, August 22.
   
• Strauss, Evelyn (1999), “mtDNA Shows Signs of Paternal Influence,” Science, 286:2436, December 24.
   
• Williams, R. Sanders (2002), “Another Surprise from the Mitochondrial Genome,” New England Journal of Medicine, 347[8]: 609-611, August 22.

* Dr. Brad Harrub serves as Director of Scientific Information, Apologetics Press. (Brad@apologeticspress.org)

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