Why does "Y chromosome Adam" date back to 200,000 years and "Mitochondrial Eve" to only 60,000 years? More..?

Question

why is it that biologist can date back are last common male ancestor for all of us (Adam) to 200,000 years ago, but the last common female ancestor ("mitochondrial eve") to only 60,000 years ago? Please explain to me the scientific reason for this....

Answer 1

Mitochondrial dating is problematic. It was long assumed that in animals, especially mammals, males did not contribute mitochondria to the offspring. Mitochondria were therefore passed from generation to generation by maternal inheritance. A.C. Wilson was one of the earliest proponents of this type of dating and he originally pinpointed the date of the last common human ancestor at ~210,000 years ago. Currently the date is estimated (by mitochondrial divergence) at ~130,000 to 160,000 years ago. I don't know where you sourced 60,000 years.

The problem with this method is that mitochondria are NOT exclusively inherited from the mother. In mammals ~5 to 10% of the mitochondria pool is inherited from the father. This confuses the numbers produced by Wilson et.al. Also, what was not known until fairly recently is that there is a LOT of DNA exchange between mitochondria (and between mitochondria and the nucleus for that matter), which also confuses that data: Wilson (at least initially) believed that the mitochondrial chromosome did not undergo recombination.

Enter the lowly Y chromosome. This is inherited exclusively through males, so everyone thought they had an accurate gage that did not recombine. Problem is that good old Y DOES recombine with the lone X in males. Even though this recombination is confined to the extreme distal end of the P arm, called the pseudoautosomal region, mistakes do happen, and sometimes "too much" DNA gets exchanged. This will confuse data from Y chromosome studies. Also, most of the Y is retro-viral in origin, with only ~30 functional genes. Therefore there is no selection pressure to maintain the DNA sequence of most of the Y and it is possible that the mutation rate on the Y is higher than the X or the autosomes. This won't alter studies showing divergence, but it can alter the time lines produced from those studies.

Bottom line is that mitochondria and Y chromosome studies have their problems and neither one should be viewed as an absolute.

Answer 2

Actually, its the other way around.  

Y-chromosome Adam (the most recent patrilineal ancestor to all humans) is estimated to have lived about 60,000 years ago, while mitochondrial Eve (the most recent matrilineal ancestor) is estimated to have lived about 140,000 to 200,000 years ago.

The reason for this is that males can make more offspring in a lifetime than females.   So a more recently living male ancestor has a higher chance of being the common ancestor to all living humans.