Your response to the above question states that there is no possibility that there was a solitary ancestor of current humanity. I thought it proper to a sense of a complete answer to the question to mention that there have been recent dissenters to this idea
There have been studies done in recent years, based on mitochondrial DNA. Mitochondria, the powerhouses of the cell that are sometimes speculated to be formerly free-living bacteria that were captured by early cells, have there own DNA system separate from that of the nucleus. As mitochondrial DNA is not recombinant (your father’s mitochondrial DNA does not mix in), all your mitochondrial DNA is inherited from your mother.
In the test performed (sorry I don’t have citations), samples of mitochondrial DNA were taken from people of wildly different ethnic backgrounds from across the globe. By comparing and contrasting the samples, comparing notes on migration and separation of races and peoples, and making speculations on the rate genetic drift (spontaneous mutations over time), it was concluded that all the world’s humanity is descended from a single female who lived some certain millions of years ago.
I don’t know how highly this study is regarded in scientific circles, or whether as of this writing it has been conclusively debunked, but I thought it deserved mention as it may be the source of the original question.
You’re talking about “mitochondrial Eve”. The choice of name is most unfortunate, since it implies she was the only human female alive at the time, like the Biblical Eve. There is a single woman from whom we are all descended in the direct maternal line. What surprised some people about the mtDNA evidence is not that mitochondrial Eve existed, but that she lived so recently (about 100,000 years ago, IIRC). This is not to say that the “mitochondrial Eve” was the only human female alive at the time, as some peopole seem to assume. By pure chance the mitochondrial DNA of one female ancestor of many from that era has become fixed, but there may well have been many thousands of human females alive at the time. We are descneded from a great many of them, but not in the direct female line.
There is also a “Y-chromosome Adam”, the man from whom we are all descended in the eirect paternal line. The last I heard, the estimate was that he lived about 250,000 years ago. Likewise, he was not the only human male alive at the time.
The most recent study (disputed, as all these kinds of research are) gives an age of 35,000 to 89,000 years for Y-guy. Science News had an article a couple issues ago. It’s not on-line, but the references are here
No, that’s not what I said. I actually said, in response to the question, “How certain is it that all humans evolved from one common primate ancestor?”:
I wasn’t trying to answer the question you bring up, and certainly didn’t say “there is no possibility.”
The mitochondrial eve studies are interesting, but don’t really prove a single “Eve.” As I said, a single group or species, yes. But there is no real way to prove a single individual.
I am curious - is there any way to determine when the actual last common ancestor lived? In other words, the last person who was a direct ancestor by any line of descent, not simply all-female or all-male?
If the last all-male line of descent ancestor lived 35K-89K years ago, then the true last common ancestor must have lived more recently than that. My guess would be that this date is likely after the general division of the ‘races’, i.e. the settlement of Australia about 25k-40k years ago. If even one person immigrated to that continent after that date, they could have become one of the ancestors to all of the people living there, even if their actual genetic contribution has vanished. (chances are that any given one of your great-great-great-great-grandparents has none of their personal chromosomes in common with you)
2[sup]6[/sup] = 64 ancestors at that distance
2*23 = 46 half-chromosomes
46 < 64
Q.E.D.
I can’t think of any simple way to determine how long ago our real common ancestor lived. The problem is that half-chromosomes (chromatids) are not handed down whole from generation to generation. Your mother’s chromatid and your father’s chromatid can exchange genes by the process of “crossing over”. This is known as “genetic recombination.” Mitochondrial DNA is not subject to recombination because it comes only from the maternal line. The Y-chromosome is likewise not subject to recombination because it comes only from the paternal line.
Slightly OT, but the most recent issue of The Global Museum (www.globalmuseum.com) cites an article which claims all Europeans are descended from 10 men.
Following some of Groundskeeper Willie’s logic, I don’t see how there could not be at least on ancestor we all have in common. Even if you assume that we are descended from a group, wouldn’t that group have a common ancestor. In fact, if there are some genes common to all humans, but not chimps, wouldn’t each one be the result of a mutation which occurred in a single individual. It seems to me that we must have several individuals from whom we are all descended. Logically, there must be an earliest such person, who would then have been the only pre-human alive at the time. (Although I am somewhat certain that that person could [and probably would] be the ancestor of at least some non-humans as well.)
Wait a minute…I just realized that there wouldn’t be an earliest common ancestor, apart from the first living cell. Damn, this is confusing. We must have had several common ancestors, but not necessarily one who was the only common ancestor alive at the time who also produced no non-human or non-pre-human descendents. But we could have. Right?
Wouldn’t it follow that if we are all descended from (among others) a single woman, that we are all also descended from her father? I mean, I know it’s not provable with mitochondrial evidence, but it seems like it would be provable with logic (assuming that the single female ancestor had been proven to exist, contrary to David B’s assertion). It’s a slight tangent, I know, but I’m curious.