Two Boingboing links

One serious: Melatonin.

"In experiments on the Japanese quail, the researchers found that melatonin switches on a recently discovered hormone called gonadotropin inhibitory hormone (GnIH), which has been found to have the opposite effect to the key hormone priming the body for sex -- gonadotropin releasing hormone (GnRH). In birds, switching off GnRH causes the gonads -- testes and ovary -- to shrink as part of the birds' yearly cycle."

And one interesting/humorous Ancient porn!

I've got one I can add to that (From Sicily, Villa del Casale Romana):