I read about 'Population Y' in David Reichs book "Who We Are and How We Got Here" (which is a good read but was a bit too in depth for me). One interesting thi

I read about 'Population Y' in David Reichs book "Who We Are and How We Got Here" (which is a good read but was a bit too in depth for me). One interesting thing in the book was how humans kept repeating this cycle: societies migrate outward and form new societies. Then one of the societies would eradicate/consume a bunch of nearby ones, form a gigantic society, and the process would begin anew. On a human timescale it is horrific and brutal but over a 50,000 year period it is interesting how we spread out but always eventually reunite with the group we split from, unfortunately in a brutal way :(.