From its initial description by Leeuwenhoek1 over three centuries ago to the discovery of its necessity for egg fertilization a hundred years later;2 the spermatozoon is now appreciated as a crucial but incompletely understood component of mammalian reproduction. Serendipitously, the Italian physiologist who first described fertilization with sperm and egg3 – Lazzaro Spallanzani – also performed instrumental experiments that helped form the genesis of germ theory and paved the way for future microbiology work by Louis Pasteur.4 Despite this serendipitous historical confluence, the notion that semen was sterile remained dogma for over two hundred years.