Last week, the International Olympic Committee announced that it will determine whether athletes are eligible for women’s events by ordering an immediate lifetime test for the male-determining gene, SRY.
But this new law raises many questions – about why “woman” is defined in this way, whether there is evidence that trans women have a chance, and whether a “level playing field” in sports is possible.
Conducting sexual experiments
In humans and other mammals, the SRY gene determines sex during the neonatal period. This type of gene initiates the development of the testes and their production of androgens – male hormones (testosterone and its products), which drive male growth.
The SRY gene is on the Y chromosome. Males have an X and a Y chromosome, while females have two X chromosomes.
Over the decades, sex tests evolved from genetic testing to using a microscope to see the second X in women or the Y chromosome in men. But the diagnosis was slow, and visually impaired athletes with sex chromosome differences.
Thus an attempt was made to detect the SRY gene directly. This is the test that the International Olympic Committee will use.
But it is not easy to know whether it is a “man” or a “woman” as you might think. The SRY gene activates a network of many genes that promote testis development or inhibit the formation of ovaries. Variations in any of these genes can produce girls with SRY or boys without SRY.
In fact, the scientist who discovered the SRY gene warned that this test is wrong for athletes with different types of genes and chromosomes.
For example, some women have an inactive version of the SRY gene that does not stimulate testis development. Some women have the normal SRY gene, and testes that produce androgens, but they have an inactive version of the molecule that activates androgens, so their bodies cannot use male hormones. The SRY test would identify these women as natural men and ban them.
Similarly, there are men with two X chromosomes who lack SRY but have other variants that transmit it. Subject to SRY’s assessment they will be allowed to compete in women’s Olympic events.
The International Olympic Committee test must take these variables into account.
What is the evidence that men have an advantage in sports?
Over the decades, physiological studies have shown men, on average, have larger hearts, more efficient lung function and larger muscles than women.
As for any characteristic, there is a wide distribution that overlaps – for example, there are tall women and short men. However, on average, there is no doubt that men are bigger and stronger than women.
Recent evidence suggests that these differences are only marginal. Almost all of our 20,000-odd genes are not on the Y chromosome and are shared by both sexes. But research in 2017 shows that about a third of our 20,000 genes work differently in men and women. Not just in reproductive cells, but in the heart, lungs, brain – everywhere. Sex differences are seen in monkeys and are evident before birth.
In the three types of muscle cells, 2,100 genes function differently in men and women. So the gender differences are deeper than we appreciated.
Traditionally, these differences have been associated with the strong effects of androgens on development at every stage – in the embryo, from childhood, especially during pregnancy.
But experiments on mice with genetically modified sex chromosomes have shown that many important physiological parameters – such as fat and energy metabolism – are not related to SRY or hormones, but to the number of X chromosomes.
And the continued health benefits provided by the Y chromosome can be seen with negative consequences when men lose it in other cells as they age.
So there are big sex differences in the function within each tissue, and it’s not all because of hormones.
But what is the evidence for the possibility of transgenderism in sports?
This is not so clear.
Going from male to female requires a change in hormones. This means suppressing androgens and taking estrogen, which is more effective in women.
This changes the body a lot. A woman born with estrogen will develop breasts and excess body fat, and lose muscle mass. His testes will also atrophy.
Trans girls can also take blockers before puberty. These drugs stop the body from producing an increase in androgens that lead to irreversible changes in the body.
So the question of whether trans female athletes have a physical advantage over cis women comes down to understanding what consistent sex differences have occurred before and during puberty in organ growth and performance, as well as any ongoing non-hormonal differences that may affect the functioning of the cells involved.
Here the evidence is conflicting, and varies depending on when and how the person passed. Some studies show significant differences in performance indicators and others do not. There is some consensus that trans women have, on average, longer legs, stronger arms and more muscles. But after two years, their heart and respiratory function is the same as that of cis women.
We don’t have data on genetic activity in trans women athletes, so there are questions we can’t answer. Do the 2,100 genes in their muscle cells return to female activity? Do other genes on the Y chromosome protect their heart and kidney function? Does the lack of a second X improve their metabolism of fat and energy?
Where is this situation?
So where does this leave the International Olympic Committee’s ban on transgender athletes? Do we need more data? Do we need to change our thinking?
I would expect that more data would confirm that trans women who have gone through male puberty, on average, have some advantages in organ size and function that cannot be reversed by hormone therapy or are not dependent on hormones. Even if the change was before puberty, the non-hormonal effects in the fetus may appear as subtle differences in function.
These differences may be minor. But cis women can assert their importance in elite sports, where competitors can win medals by running or swimming 0.01 seconds faster than everyone else.
Like most attempts to control human behavior, this restriction created human differences.
Further complicating matters, there is already a large physical disparity among cisgender athletes in the characteristics that make them excel in sports. For example, the variation in androgen levels has sparked calls to restrict hyper-androgenised women and to mandate permitted hormone levels.
This is a bit sad – are we banning exceptionally tall women from playing basketball?
Participation in sports is important for health and social relationships. Sometimes it saves the lives of trans women.
So discussing alternatives – such as open competitions alongside the Olympics, or categories based on something other than sex – remains important.
But maybe we should believe that the stadium will never be in the real world. Elite athletes are probably off the charts in many physical and physiological characteristics. Is this okay with all of us?
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