Jarrett and Xochitl are discussing the meaning of "genetic differences."
Xochitl guesses that the genetic difference between girls and boys are that boys have penises and girls have long hair.
Jarrett: Well... yes. What animal do you think humans are most like?
Xochitl: Monkeys, because monkeys have thumbs like us, and ducks do not. They have webs, and in fact they don't even have hands, they have feet.
