All our other chromosomes come in neat pairs, but men inherit a messy pair of unequal sex chromosomes--gangly big X and stunted little Y.
Not exactly a riveting passage. BUT, for non-fiction, this is a pretty interesting (and quick-reading) book. Here's a better quote from page 47:
So, some animals have no sex at all, some animals can be either sex, and some animals decide what sex to be on the basis of where they are, how hot they feel, or which of their friends happen to be nearby.