Boule, a gene that makes sperm, is found to be almost universal in the production of animal life. It's found in flies, fish, birds, dogs, and us.

"This is the first clear evidence that suggests our ability to produce sperm is very ancient, probably originating at the dawn of animal evolution 600 million years ago," said Eugene Xu, assistant professor of obstetrics and gynecology at Feinberg. "This finding suggests that all animal sperm production likely comes from a common prototype."

When Xu's research group knocked out the Boule gene from a mouse, the animal appeared to be healthy but did not produce sperm.