I've heard that anthropologists are in disagreement about the origin of Homo Sapiens. Some believe that Sapiens evolved from Homo Erectus in Africa, before exploring the world. There are those that believe all Homo Erectus evolved into homo sapiens around the same time, well after Erectus left Africa.
If I could just concentrate on the latter scenario. Suppose at some given interval of time homo erectus did evolve into modern man no matter where they were on the planet. Could it be possible that the human genome or that of any creature contains a gene that at a certain time triggers a major mutation? A built-in time delayed gene so to speak. Like onco genes that need something to trigger them.