Determine which process of evolution is likely impacting the population below. Once you have determined the process, briefly explain why you selected that process.

1. In 1955, Ronald Ubba set up a long-term study cataloging the blood types of chimpanzees in Gombe National Forest. Initially, there were no individuals with blood type B. Five generations later, a new neighboring group of chimpanzees moved into the area and began exchanging mating partners with the original study population. Ronald Ubba found that there were now several members with blood type B. Which process of evolution is likely affecting this population?