Rationale behind Most Recent Common Ancestor (MRCA)?
any giving individual alive today will be either an ancestor to ALL of the humans (in that future time) or none of them. What is the rationale behind this?


It's a simple mathematical observation nothing more than that.

One that doesn't actually require doing any math to understand.

Take a few billion people, let them mix &amp; breed freely within the confines of a limited environment (the world) &amp; eventually (after enough generations) every single one of the current population will be be related &amp; therefore descended from every single one of the original population that have any surviving descendants.


Those whose line doesn't die out will inevitably be an ancestor of every living person at a future generation, eventually.
Those who die with no offspring or have last-descendants do it for them, have no descendants.


It's just a simple statement of something that's obvious when you think on it.