William is a graduate student interested in studying the genetic influences on sexual orientation. one of the first things that william learns is that

The most prominent theories of the genetic basis of sexual orientation state that homosexuality has a partially genetic basis. Another prominent theory states that two gene variations on the male X chromosome have an influence on whether males grow up to be heterosexual or homosexual. It is likely that William will learn these two phenomena when investigating the genetic influences on sexual orientation.

Pilgrims is the answer