Assume that in a small population, 15 percent of the people are blue-eyed and have brown hair. Assume further that within this population, there is an adventurous group that wishes to explore the region and settle down in new territory. Of this adventurous group, 87 percent are blue-eyed and have brown hair. When they leave, the gene frequencies in the remaining population will change for blue-eyes and brown hair in the next generation. This is an example of .