3 ms·

From my reading of the above, the “most recent common ancestor” is a single individual who acts as a common ancestor to all alive today Whereas “identical ance

by setr 5y ago

From my reading of the above, the “most recent common ancestor” is a single individual who acts as a common ancestor to all alive today Whereas “identical ancestors” is a time period where everyone alive is an ancestor to those living today. So a group of ancestors are being selected — rather than just the one. So this should generally always be closer to now than the “single recent ancestor”, simply by virtue of allowing the ancestor tree to be more splayed out. However, my understanding of the latter must be wrong, because yesterday would always be the most recent time period holding true to that definition — or if it only counts if none of the people alive today are alive in the identical ancestor time period, then it’s always going to be today - current oldest human’s age - 1 day.

ml_basics 5y ago
My reading was that the “identical ancestors point" is the point at which every person is either: 1. an ancestor of all currently living people; or 2. an ancestor of no one currently living (ie their line died out). Alternatively, it’s the time when all currently living humans have exactly the same set of ancestors. Whereas “most recent common ancestor” means that the intersection of ancestries of all living people is non-empty. (That intersection being the common ancestor)
zuminator 5y ago
During the "most recent common ancestor" period, as you said, there's a single individual who acts as a common ancestor to all those alive today. Let's for sake of argument say that person is Genghis Khan, that Genghis Khan is somewhere in every current living person's family tree. How about Genghis's parents? Mr. and Ms. Khan (actually Yesugei and Hoelun) are surely BOTH common ancestors to everyone alive today. And surely Grandpappy Khan and the other three grandparents, and so on, going back. That ancestral tree keeps growing and eventually, you'll get to the point in the past that everyone alive at that period is an ancestor to Genghis Khan. Which means they are all also in our family tree. Therefore we all have an identical looking family tree from that point backwards.

by setr 5y ago

ml_basics 5y ago

My reading was that the “identical ancestors point" is the point at which every person is either: 1. an ancestor of all currently living people; or 2. an ancestor of no one currently living (ie their line died out). Alternatively, it’s the time when all currently living humans have exactly the same set of ancestors. Whereas “most recent common ancestor” means that the intersection of ancestries of all living people is non-empty. (That intersection being the common ancestor)

zuminator 5y ago

During the "most recent common ancestor" period, as you said, there's a single individual who acts as a common ancestor to all those alive today. Let's for sake of argument say that person is Genghis Khan, that Genghis Khan is somewhere in every current living person's family tree. How about Genghis's parents? Mr. and Ms. Khan (actually Yesugei and Hoelun) are surely BOTH common ancestors to everyone alive today. And surely Grandpappy Khan and the other three grandparents, and so on, going back. That ancestral tree keeps growing and eventually, you'll get to the point in the past that everyone alive at that period is an ancestor to Genghis Khan. Which means they are all also in our family tree. Therefore we all have an identical looking family tree from that point backwards.