In Relation to Humanity's Global Spread, the 'Replacement Hypothesis' Describes

In relation to humanity's global spread, the 'replacement hypothesis' describes the idea that groups that left Africa early to occupy territory on other continents (early immigrants) were:

A) killed off by diseases introduced by later immigrants
B) killed off by later immigrants through acts of violence
C) driven out of the new territory by later immigrants, who then took over the territory
D) unable to adapt to the new environment and so died off and left it open for new immigrant groups who arrived later on and were somehow more successful at adapting
E) All of the answers are correct