Also a lot of assumptions about mutation rate. Anatomically modern humans appeared 300k years ago. Behaviorally modern humans appeared 50k years ago.
A species beginning colonization on one end of the galaxy might not be the same species at all by the time it reached the other end of the galaxy a million years later. There might be a whole spectrum of new species that emerged along the way.
A species beginning colonization on one end of the galaxy might not be the same species at all by the time it reached the other end of the galaxy a million years later. There might be a whole spectrum of new species that emerged along the way.