Explanation for those whose high school bio lessons were subpar: every fetus starts out with genitals that appear to be a vagina with a disproportionately large clit. If you've got the SRY gene on one of your chromosomes, the clit becomes your dick and the proto-labia fuse and become your balls. This is why your balls (if you have them) have a vertical seam at their midsection; that’s where your labia fused. So, it's often said that we all start out female.