Evolution has shaped every part of the body, and that includes our private parts. New research published this week sheds light on how the penis evolved and how it forms in different animals.
The research might also one day help illuminate a medical mystery: Birth defects of the penis have risen sharply in recent decades, and nobody is sure why.
Penises weren't necessary when our early ancestors lived in the ocean. A female could lay eggs, and a male could just swim by and excrete some sperm. It would all mix and fertilize in the water.