Evolution Is So Random - The extraordinary case of the Guevedoces

This means we should treat different sex and sexuality with care, humility and embrace diversity of life on earth.  

Yes, there are few people who take advantage of this but yet there are millions more who need our support who suffered silently for centuries. 

This piece from 2015 blew my mind (via here): 

The discovery of a small community in the Dominican Republic, where some males are born looking like girls and only grow penises at puberty, has led to the development of a blockbuster drug that has helped millions of people

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So why does it happen? Well, one of the first people to study this unusual condition was Dr Julianne Imperato-McGinley, from Cornell Medical College in New York. In the 1970s she made her way to this remote part of the Dominican Republic, drawn by extraordinary reports of girls turning into boys.

When she got there she found the rumours were true. She did lots of studies on the Guevedoces (including what must have been rather painful biopsies of their testicles) before finally unravelling the mystery of what was going on.

When you are conceived you normally have a pair of X chromosomes if you are to become a girl and a set of XY chromosomes if you are destined to be male.

For the first weeks of life in womb you are neither, though in both sexes nipples start to grow.

Then, around eight weeks after conception, the sex hormones kick in. If you're genetically male the Y chromosome instructs your gonads to become testicles and sends testosterone to a structure called the tubercle, where it is converted into a more potent hormone called dihydro-testosterone This in turn transforms the tubercle into a penis. If you're female and you don't make dihydro-testosterone then your tubercle becomes a clitoris.

When Imperato-McGinley investigated the Guevedoces she discovered the reason they don't have male genitalia when they are born is because they are deficient in an enzyme called 5-alpha-reductase, which normally converts testosterone into dihydro-testosterone.

This deficiency seems to be a genetic condition, quite common in this part of the Dominican Republic, but vanishingly rare elsewhere. So the boys, despite having an XY chromosome, appear female when they are born. At puberty, like other boys, they get a second surge of testosterone. This time the body does respond and they sprout muscles, testes and a penis.

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Another thing that Imperato-McGinley discovered, which would have profound implications for many men around the world, was that the Guevedoces tend to have small prostates.

This observation, made in 1974, was picked up by Roy Vagelos, head of research at the multinational pharmaceutical giant, Merck. He thought this was extremely interesting and set in progress research which led to the development of what has become a best-selling drug, finasteride, which blocks the action of 5-alpha-reductase, mimicking the lack of dihydro-testosterone seen in the Guevedoces.

My wife, who is a GP, routinely prescribes finasteride as it is an effective way to treat benign enlargement of the prostate, a real curse for many men as they get older. Finasteride is also used to treat male pattern baldness.

A final interesting observation that Imperato-McGinley made was that these boys, despite being brought up as girls, almost all showed strong heterosexual preferences. She concluded in her seminal paper that hormones in the womb matter more than rearing when it comes to your sexual orientation.