When cases were first confirmed in the Dominican Republic, “Guevedoces” changed much of what scientists knew about gender at the time. These extraordinary children are born resembling and acting like women, but at puberty, they begin to grow penises and transition into living life as a man.
The unusual developmental processes of the Guevedoces gave them their name, which is colloquial Spanish for “penis at twelve.” They are only known to exist in isolated regions of the world, most notably in remote regions of the Dominican Republic and Papua New Guinea, where they are called “turnims,” or “expected to become men.”
Dr. Julianne Imperato of Cornell University was among the first researchers to travel to the land of the Guevedoces in the 1970s. At the time, their existence was considered the stuff of legends in academic circles, but Imperato soon discovered that the legends were completely true. She set out to understand the biological understandings of a Guevedoce.
Fetuses are essentially genderless for the first few weeks of existence. After eight weeks, sex is determined. If you are female, your gonads develop into a clitoris. If you are male, your Y chromosome causes your gonads to develop into testicles, which in turn release testosterone that is sent to the tubercle. The testosterone is transformed into the stronger dihydro-testosterone via an enzyme called 5-alpha-reductase, and the dihydro-testosterone converts the tubercle into a penis.
In the case of a Guevedoce, the Y chromosome is present and leads to the formation of testes. However, fetal Guevedoces lack sufficient quantities of 5-alpha-reductase to transform the tubercle into a penis, leaving a vagina in its place. When a Guevedoce hits puberty, the development of male genitalia is “completed” thanks to the marked increase in testosterone production. The condition is genetic, which explains its geographical concentration in certain parts of the world.
Despite the incredibly late appearance of a Guevedoce’s penis, Imperato found that they function identically to those of a man born with male parts. The vast majority of Guevedoces adjust to living as a man – even though many of them had lived as a girl prior to puberty.
Imperato made another important observation about Guevedoces: they have abnormally small prostates. In 1974, her findings landed in the hands of Merck head researcher Roy Vagelos, who set about creating a drug that would mimic a Guevedoce’s development by blocking 5-alpha-reductase production. Vagelos had stumbled upon the idea for finasteride, an incredibly significant drug with applications in treating enlarged prostates and hair loss in men.
Despite their differences, Guevedoces are welcomed into the fabric of their society from an early age. After their penis grows, Guevedoces have almost no difference in their quality of life compared to anyone else in their villages. Nearly all of them were found to be heterosexual and could start their own families at the same age as men who were born with male genitalia.