Evolution 2

"On behalf of all organisms that have ever lived: not a single one of our ancestors died before they reached adulthood and begot at least one child. In a world where most organisms die before they can procreate, descendants are common but ancestors are rare. But we can all claim an unbroken chain of successful ancestors all the way back to the first single-celled organism."

The matrilineal nearest common ancestor to all of humanity is the Mitochondrial Eve. In other words when you trace back all of the females who ever lived from there mothers to their grandmothers and so on. In short all living humans today are related to this one person by at least one parent. This was done using a process of tracing the human lineage back words through mitochondrial pathways. Now this is not to say that the Mitochondrial Eve was the only female of her era. She lived among an entire population of males and females but she is special because only her ancestors survived until now. Now the Mitochondrial Eve is also not our most recent common ancestor but only the matrilineal nearest common ancestor.
"The MRCA answers the question, "Do any of my four grandparents overlap with any of your four grandparents? If not, then do any of my 8 great grandparents overlap with any of your 8 great grandparents?" Between one-hundred and two-hundred generations back, a single person will appear in every living person's family tree. However, each person has only one mitochondrial ancestor with each generation backwards because each person inherits their mitochondria from their mother. The question of "when did Mitochondrial Eve live?" is answering the question of "When does my mother's mother's mother ... overlap with everyone else's mother's mother's mother ... (all the way up the female lineage)?"
Since we are all born with Mitochondria from our mothers Scientist need only to trace this Mitochondria back til they reached Mitochondrial Eve.

This Mitochondrial Eve is believed to have lived 170,000 years ago in Africa. She was an anatomically modern Homo Sapien and lived in a time before humans began to migrate out of Africa and into the rest of the world.

Y chromosomal Adam is an entirely different story. Now Y chromosomal Adam and Mitochondrial Eve lived at entirely different times. Adam was an african man who lived 60,000 years ago.

"By analyzing the Y-chromosome DNA from males in all regions of the world, geneticist Spencer Wells has concluded that all humans alive today are patrilinealy descended from a single man."

Y chromosomal Adam is the only man from his time to have a single unbroken family line to modern day similarly to Eve their contemporaries had family lines that would eventually end.

It's kinda interesting that not relatively not that long ago all of our common ancestors lived in Africa not knowing that their family lines would continue for so many generations. Even still this is only the tip of ice burg when compared to the Universal common ancestor who is in other words every living creature on earths ancestor.