If
a geological barrier (like a continent splitting apart) separates a
population of primates, then each population will evolve separately to
fit the different conditions of their environments.
As a hypothetical example, if one part of Pangea went north, the
primates on that part would adapt to cold temperatures. If the other
part went toward the equator, those primates would adapt to heat and
direct sunlight. Eventually they would evolve into different species
over many generations.
