Fallon Fox won her last mixed martial arts fight in 39 seconds. It was March 2, at the Bank United Center in Coral Gables Florida. Fox squared off with her opponent Ericka Newsome and exchanged a few punches in the center of the cage. Fox threw Newsome to the canvas, but she bounced back up. Then Newsome tripped Fox up, who recovered her feet quickly. They clinched and Newsome began throwing heavy punches to the body. Fox absorbed the blows and secured a grip on Newsome's head. She took three, four, five unanswered punches to the ribs, but seemed unfazed. With her hands gripping the back of Newsome's skull, she delivered a massive knee, bringing her leg up while pulling her opponent's head down. The blow landed on Newsome's chin and dropped her, unconscious, face first on the mat.

It was Fox's second fight and second victory as a pro MMA fighter. She was excited, especially about the chance to try out for a spot in the UFC, the sport's biggest league, which had just added a women's division. But on March 5, in an interview with OutSports, Fox revealed to the world that she was transgender. She had been born a man, but over the past six years, had become a woman with the aid of hormone therapy and sex reassignment surgery.

The response was immediate and overwhelming. Numerous female and male fighters, trainers and promoters condemned Fox, saying it was unfair and downright dangerous for a man to step into the cage and combat a woman. UFC commentator Joe Rogan ripped into Fox on his weekly podcast:

She wants to be able to fight women in MMA. I say no fucking way. I say if you had a dick at one point in time, you also have all the bone structure that comes with having a dick. You have bigger hands, you have bigger shoulder joints. You’re a fucking man. That’s a man, OK? You can’t have… that’s… I don’t care if you don’t have a dick any more.

Rogan's comments highlight the two central themes playing out in this controversy. First, does Fox have a physiological advantage that makes competing against biological women dangerous or unfair? And second, is the world ready for transgender athletes? Rogan, himself a black belt in Tae Kwon Do and Brazilian Jiu Jitsu, makes some basic points about Fox's physical advantages, but is clearly reacting more out of emotion and revulsion than common sense.

Interestingly, Rogan's points are not necessarily supported by the current science. The International Olympic Committee changed its regulations in 2004, allowing transgender athletes to compete two years after sex reassignment surgery. Fox, who is 37 years old, travelled to Thailand in 2006 and underwent her surgery. She has been on hormone replacement therapy since.

There is precedent for transgender athletes in combat sports. Brazilian Judo player Edinanci Silva competed in the 1996 games before revealing that, at puberty, she had both male and female sex organs. Silva placed seventh that year, and was allowed to continue competing as a woman internationally. Transgender male to females have also competed in golf, cycling, and tennis. All of these sports, including Olympic Judo, are significantly less violent than mixed martial arts.

"Some people believe I have an automatic advantage over other female MMA fighters. 'She has to be stronger because was a male!' But if they look into the science of it, what the hormones do to the body...[the strength], it dissipates," Fox told OutSports. "That's one of the reasons the International Olympic Committee has allowed post operative trans people to compete."

Dr. Marci Bowers, who has performed hundreds of sex reassignment surgeries told our sister site Bloody Elbow that Fox wouldn't have much of a physical advantage, nothing beyond the normal variations in body type that exists among biological females. "Most measures of physical strength minimize, muscle mass decreases, bone density decreases, and they become fairly comparable to women in their musculature. After as much time as has passed in her case, if tested, she would probably end up in the same muscle mass category as her biologically born female counterpart."

But not all doctors agree with her. Dr. Ramona Krtuzick, an endocrinologist well versed in the finer points of hormone therapies, says that because Fox started her treatment so late in life, it's unlikely her skeleton and musculature would change significantly. As Krutzick told Bloody Elbow:

Typically, you're looking at about 15 years after androgen suppression and sexual reassignment surgery to really start to see significant changes in bone density. It's been too early for her to see much of a decrease in bone mass or to make her equal to that of a female. She started off with a much higher bone density than other women her same age, and therefore will maintain a lot of that for a while. Additionally, because she is taking estrogen, that will actually help to maintain that bone mass. Women also have lighter, child bearing hips because of the difference in hormones during the body's developmental years. Her skeleton and body mass and shape developed a long time ago. Those changes cannot be undone. They are permanent.

Her testosterone levels are more than likely in the normal female range, since her adrenals are the primary source for it now. She didn't undergo hormone therapy and surgery until she was fully developed, as compared to someone who completes therapy and surgery in their adolescence or very early adulthood, when they haven't completely developed. She has the potential to be significantly stronger because her muscle development reached several years beyond full maturity, giving her the potential to be significantly stronger than other age matched women.There's not really a way to determine how much her muscle mass will decrease over time. What can be said is that she has a naturally higher propensity to build and maintain muscle mass because she was once a fully developed, adult male. You can't ever take that away from her.

For now it's unclear if Fox will be able to obtain a license from a state athletic competition to continue competing in MMA as a woman. Florida and California are considering her case. Her next scheduled opponent, believes its wrong for Fox to fight as a woman, but plans to compete against her anyway. Female fighter Rosi Sexton, took a remarkable nuanced position on her blog. "I agree that equality of participation is a nice ideal, and it’s a reasonable argument if we’re talking about sports like tennis or kayaking. But in a sport where one participant is trying to do physical damage to another, the burden of proof should be reversed. We need good scientific evidence to support the assertion that Fox has no advantage as a result of having been born male."

It seems clear that what matters to most female MMA fighters is not the idea of battling a man, but being able to go into the fight fully informed. "I sympathise with Fox’s position, and I don’t entirely agree with those who say that she should not be allowed to fight," wrote Sexton. "On the other hand, I believe it was wrong that Fox’s opponents were not informed of the situation so they could make their own assessment of the risks involved and give consent."

There is no small irony that the history of mixed martial arts, from the Brazilian tradition of Vale Tudo to the first UFC events in the United States, was searching for the toughest fighter on the planet. The size and strength difference between the contestants in the earliest UFC events was far more extreme than what Fox would possess, fighting as she does in modern MMA, with tightly regulated weight classes. If her female opponents are comfortable fighting her, they can take courage in the fact that Royce Gracie, the UFC's first champion, defeated multiple opponents in a single night who outweighed him by over 100 pounds. The UFC's former lightweight champion, Frankie Edgar, didn't take part in the very common practice of cutting weight before a fight, meaning he was often 20-30 pounds lighter than his opponents the night of the match. It didn't stop him from rising to the top of his division and winning the belt.

Martial arts has always stressed that technique, not size and strength, are what matters in combat. With informed consent, perhaps transgender athletes are the perfect opportunity to test that theory.