Have you ever heard of a type of human that is born one sex then "transforms" at puberty to a different sex? That means you've never heard of "Guevedoces". Don't feel bad because until a few days ago... I hadn't either.
"Guevedoces" which literally translates to "penis at twelve" is a term given to little girls in the village of Las Salinas in the Dominican Republic who turn into boys at puberty. Do I know how crazy that last sentence sounds? YES! But it's true. The boys of Salinas have a rare genetic condition which blocks them from producing the hormone Dihydro-testosterone while their in the womb. Dihydro-testosterone, is the hormone which assigns male sex organs to a fetus. Unfortunately for "Guevedoces" they don't get the required amount of Dihydro-testosterone until they hit puberty and get a second surge of growth hormones.
In my travels I've heard of the "Hijra" of south Asia, but this is different. Hijra is a term for transgender people also known as the third gender in southern Asia. Let's be clear..."Guevedoces" are not transsexual's. All transsexuals who transition from their assigned gender to the gender they identify with, need surgery to achieve their goal. Guevedoces, are real transforming humans whose transition occurs naturally (without surgery) due to their rare genetic disorder. When they're born Guevedoces appear to have a vagina and no testicles so most medical facilities classify the newborns as female. The exact cause of their appearance is a lack of 5-α-reductase enzyme which triggers the hormone surge that releases the Dihydro-testosterone.
All fetuses develop internal glands called "Gonads" and a bulge between their legs called a "Tubercle". In normal child development the sex organs develop on a fetus around the eighth week. At that time male babies start producing Dihydro-testosterone in large amounts, which turns the tubercle into a penis. While female fetuses produce a different hormone which turns the tubercle into a clitoris. Unfortunately for Guevedoces this transformation occurs twelve years later. Usually after being forced to wear girls clothes and have a girls name for the majority of their youth.
For more information on "Guevedoces" and their unique genetic lineage watch the video below.