In 10th century norway, eric the red and his followers were banished for murders and general rowdiness. this small group, which
had a higher representation of an allele that contributes to red-hair color than the rest of the population of norway, sailed west and established a colony on iceland. within several centuries this colony had a population of several thousand, the majority of whom were red-heads. this is best explained by
This is a typical case of natural selection, where we have a group of people that have similar physical traits, that are selected and than isolated from any external influence, so with interbreeding they manage to keep their physical traits for generations to come and thus create a population that resembles their initial ancestors.
I believe that they are similar because they are stating one of their traits, and helping you find out how much the two subjects have in common and how different they are
