Monday, April 12, 2010

NOVA Online | Neanderthals on Trial | Tracing Ancestry with MtDNA

I was sent the following article rebutting my contention that all living people have mitochondrial DNA from one woman. The article begins as follows

n 1987, three scientists announced in the journal Nature that they had found a common ancestor to us all, a woman who lived in Africa 200,000 years ago. She was given the name "Eve," which was great for capturing attention, though somewhat misleading, as the name at once brought to mind the biblical Eve, and with it the mistaken notion that the ancestor was the first of our species—the woman from whom all humankind descended.

The "Eve" in question was actually the most recent common ancestor through matrilineal descent of all humans living today. That is, all people alive today can trace some of their genetic heritage through their mothers back to this one woman. The scientists hypothesized this ancient woman's existence by looking within the cells of living people and analyzing short loops of genetic code known as mitochondrial DNA, or mtDNA for short. In recent years, scientists have used mtDNA to trace the evolution and migration of human species, including when the common ancestor to modern humans and Neanderthals lived—though there has been considerable debate over the validity and value of the findings.
Th article then spends time on explaining the difference between mitochondrial DNA and nuclear DNA (the DNA from both parents in the nucleus of our cells). Then the article tries to explain why the Bible is wrong if we are all truly descended from a single woman.
Let's get back to "Eve." The ancestor referred to in the 1987 Nature article can be more precisely stated as "the most recent common ancestor through matrilineal descent of all humans living today." In other words, she is the most recent person from whom everyone now living on Earth has inherited his or her mtDNA. This certainly does not mean that she is the ancestral mother of all who came after her; during her time and even before her time there were many women and men who contributed to the nuclear genes we now carry. (To see how this can be, check out Tracing Ancestry.) It also does not mean that the mtDNA originated with this "Eve"; she and her contemporaries also had their own "most recent common ancestor though matrilineal descent," a woman who lived even further into the past who passed on her mtDNA to everyone living during "Eve's" time. (We get our mtDNA from that same, older ancestor. She's just not, to us, the most recent common ancestor.)

So what about all of the mtDNA of the other women who lived during "Eve's" time? What happened to it? Simply this: Somewhere between now and then, they had female descendants who had only sons (or no children). When this happened, the passing on of their mtDNA halted.
Okay, let me get this straight: This one woman we are all descended from had other people with her  and they had ancestors and the reason why there are no other people with different mitochondrial DNA because every single contemporaneous woman either had all male offspring or no children at all! That makes about as much sense as pulling a pinto out of my.....but I digress. I am amazed at the contortions people will go to even remotely entertain that the Bible is right.

NOVA Online | Neanderthals on Trial | Tracing Ancestry with MtDNA
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