which factor played a large role in human evolution?

Question

A-a geologic event that released much radiation into the enviroment, which in time resulted in a high mutation rate
B-climatic changes that caused existing primates to search for new food sources
C-flooding due to melting glaciers causing primates to seek refuge in trees
D-massive grassland fires that caused existing primates to flee to the mountains

Answer 1

B. Climate changed forced migration of existing primates, splitting them into geographically isolated groups. Smaller groups either died or survived, depending on whether they found suitable food. This produced a adaptive pressure and resulted in evolution of different species from the original, larger group, particularly if the geographic separation was sustained.