Psst. Hey guys, your penis could've been a vagina

Most people think that male and female genitals are about as different as can be: penis = male and vagina = female. But even this basic dichotomy is not really correct: the genitals emerge from the same mass of embryonic tissue. For the first six weeks of development the tissue masses develop identically.  At about six to seven weeks, depending on whether the fetus has XX or XY chromosomes (usually), the tissues start to differentiate. One part of the tissues begins to form the clitoris or penis and another forms the labia or scrotum. Another area begins to form into either the testes or the ovaries. This means that physiologically, male and female genitals are made of the same stuff and work in similar ways.

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