CSI: Crime Scene Investigation, Season 5

Grissom:
I thought you'd want to know what happened to Wendy.

Mimosa:
I appreciate your telling me. Killed by someone in our own community. As if we don't have enough enemies. Her parents never understood her, but still I think they should know. What do I say?

Grissom:
Show them an oyster.

Mimosa:
I'm sorry?

Grissom:
There are two types of male oysters, and one of them can change genders at will. And before man crawled out of the muck, maybe he had the same option. Maybe originally we were supposed to be able to switch genders, and being born with just one sex... is a mutation.