A large population of mice (2000 individuals) lives in an area dominated by small shrubs in the desert. When the population size got too high, a small group of 6 individuals left and colonized an area adjacent to the original population's home, but this area is primarily dominated by trees instead of shrubs. There is no gene flow between the dispersers and the original population. A researcher sequenced the genomes of representative individuals from both populations and found substantial genetic differences between them. Which of the following would MOST account for the amount of genetic differences observed?

Divergence between the two populations was caused solely by drift.
Since the original dispersal event, the small population will have evolved more than the large population.
Divergence between the two groups is high because of gene flow between them.
The divergence between populations could only have been caused by stabilizing selection.

When the group of 6 individuals left and colonized an area that was different to their initial home, they had to adapt to the new environment and new food resources. Offspring from the small population that had more advantageous characteristics had a better chance of survival than those that did not.

The offspring that had the better chance of survival were the ones that inherited new traits that helped survive in their environment with more trees and thus they would breed with other mice that also survived, passing on these traits to their offspring. The mice that did not inherit these traits, could not survive well and probably died.

The mice from the original population did not need to inherit as many new traits as they were in a familiar environment and thus did not evolve as much as the smaller population.