Last week, I posted a thread addressing a common criticism of transgender athlete policies, namely that they’re based on evidence in non-athletes. Here’s that thread, for a reminder. Today, I want to mull on another common issue raised in objection: https://twitter.com/Scienceofsport/status/1297915789530497025 (1/)

The objection is this: People argue that because trans women are often smaller, lighter, slower, weaker etc than biological females, it should be fine for them to compete as women. It’s an “overlap argument". Here’s one example of that thinking (this particular poll backfired):

The premise of the argument is this:
- Testosterone confers upon males advantages including size, strength, speed, power. This is why women have a separate category;
- If someone identifies as female (trans women), provided they’re not too big, strong, fast, they can compete as W

This leads the argument that trans women inclusion should be dealt with on a case by case basis. If you measure & limit enough variables, problem solved! Right?
Well, no, and I just want to think out loud about some issues. Here’s an example of the actions it calls for (4/)

So, first, let’s begin by recognising that there IS overlap between M & F in pretty much every variable we can think of associated with sport. Many women are faster, stronger, heavier, taller than many men. This is obvious. How many of you men are faster than Radcliffe? Yep (/5)

We can (and have) quantified this for mass in rugby, for example. See figure below - the typical male is slightly heavier than the 99th percentile for females (the heaviest 1% of women almost as heavy as typical males). So there is clearly overlap in each attribute, independently

The argument now is that some trans athletes, those who overlap and are lighter than males, should be included because if mass is the problem, they create no problem. Except…couple of things. First, mass is not the only thing that matters. It’s one of many attributes that drive

…performance and safety risk. Even at the same mass, evidence is compelling that men are stronger than women. In fact, to match strength, you often need a male who is 20% to 30% lighter than a female. So simply focusing on mass misses many of the factors for safety & performance

But more to the point, where do you set a threshold? Should it be 75kg? 90kg? 60kg? No matter where you set it, the group of humans who fall just under it, AND who have strength & speed advantages would all be male. So this idea of ‘limits’ is a shortcut to ‘no women in sport'

Second, it’s a misunderstanding of why categories exist. Do you allow a 27 year old adult to play against 17 year old children if they’re “a bit smaller than average and not that strong”? Would you allow a weak heavyweight to fight middleweights just because they lack strength?

In other words, why make an exception that allows someone to cross into a protected category just because that person lacks the attributes that category is associated with? The sexes are divided by sex, not weight/strength etc, even though they may be correlated with it.

Next, a philosophical question - if sport is to set up some kind of ‘bright line test’ to decide which applicants for women’s sport should be allowed in and which should not, how does one draw that line? Is sport going to decide who is “womanly enough” for sporting purposes?

On what basis might sport decide that person A cannot play women’s sport, but person B can? Some complex algorithm that factors in all the relevant attributes? Think of how that would be tested. It’s more discriminatory than ever, and lacks rigor and integrity. I can’t see how

…sport can be tasked with running that test. It would also have to be ‘cheat proof’ (look at paralympic classification for why), done regularly, and it would need to be absolutely accurate, or it would not address the risk issues anyway. I don’t know what these tests look like?

In short, the “overlap” argument seems to me to argue for a new way to categorise people for sport, and it’s one that would end women’s participation in sport, because wherever you draw a bright line, biological males will have performance advantages in other attributes around it