Refer to the scenario below, and then answer the following question(s).
Two European men and two Polynesian women settled on a previously uninhabited tropical island. All four of the settlers have brown eyes, a dominant trait, but one of the Europeans is heterozygous and carries the recessive gene for blue eyes.
-No new settlers arrive, and nobody leaves the island. After a few generations, the percentage of blue-eyed individuals increases from the original zero to 25 percent. This is probably due to which of the following factors?