ROOT (Y-ADAM)

MCRA

As I mentioned in my first post I was struggling with the concept of “Mitochondrial EVE and Y-chromosome Adam”. The actual name of these people is Most  Recent Common Ancestor (MRCA). My cousin and I have an MCRA in our shared grandfather. The “Mitochondrial EVE and Y-chromosome Adam” (both of these were named in honor of the biblical Adam and Eve) are the MCRA of the human race.

The theory is that every female mtDNA goes back in time to a single female ancestor and every male's Y-DNA goes back to a single male ancestor.  This Adam and Eve need not have been mates and may not have even lived at the same time. Remember that the female hands her mitochondrial DNA down from generation to generation in tact except for the occasional mutation. The male does the same with his Y-DNA.

The first premise is that everyone goes back to a single entity, even if we have to go all the way back to the first creature that crawled out of the ocean to become our first mammal. More likely it goes back at least to the first homo erectus that mutated into a homo sapien. So we can reasonably assume there is at some point a common ancestor for both the male and female lines. 

The next part of the theory, to determine the most recent common ancestor,  says that for a male or female to be the MCRA they must have had at least two offspring of their sex that went on to have descendants all the way to today. Obviously if a female has only male offspring that survive to today then that mitochondrial DNA line dies out. The rest of the DNA could be passed on in other cells, but the mitochondrial line dies out. If a male only has female offspring that survive then that Y-DNA line dies out similarly. This is actually fairly common and probably even more common in the past when life expectancy was much shorter. Also, if someone only had one offspring that has descendants that made it to today then they are not the MOST RECENT, so the title must move down in generations until you hit the person with two. If in any given time frame such as today or 10,000 years ago, there is more than one person living with two or more offspring then you have to keep going back in their ancestry until you get to the MCRA of those people.

DNA research today suggests the the male MCRA goes back a little over 200,000 years, consistent with the emergence of modern humans. The same estimate for the female MRCA is 100,000 to 200,000 years ago. Obviously DNA research is still pretty vague in its time frame calculations.

Most scientists believe there were probably 10,000 or so humans in existence when these MCRAs lived but all other mtDNA and Y-DNA lines have since died out. The reason they believe this is because in the rest of our DNA which is randomly inherited from our parents there is enough variation to suggest this. You see we have inherited the DNA from the rest of the people alive at the time of the MCRAs as well, just not in the Y-chromosome DNA or in the mitochondrial DNA. This is why the male and female MCRAs did not have to be mates or even live at the same time.

Recently a problem with the female MRCA has arisen. There is some evidence that the mtDNA may be partially inherited from the father. If this is true then the whole theory of “Mitochondrial Eve” as it is described here is gone. http://www.trueorigin.org/mitochondrialeve01.php 

I found this to be fascinating. I also wonder if my explanation is clear. Feel free to ask questions if I am unclear.