Glass looks at the available examples of both phenomena.

"...I'm not sure," she says. "I don't think it's consistently the same on high layers, but there is something going on, on high layers. On low layers the werewolves are only choosing from among people who they could have children with were they so inclined and the vampires are only choosing people with compatible orientations, but I can't make out any patterns in what else is governing this."