There was also this from Dr Emma Hilton about height with charts and graphics:
https://x.com/FondOfBeetles/status/1856720482583638038?s=20
Twitter 13th November 2024
Why male advantage in sport is not a social construct: height. Height is a key difference between males and females. What is nature v nurture? What does that mean for sport?
Bigger skeletons are most obviously driven by longer bone growth. Key bones like those in your thigh (“long bones”) grow from their end to get longer, making you taller.
The site of bone lengthening is called the “epiphyseal plate” or “growth plate”. Here, cells divide/enlarge, making new tissue that pushes the bone ends apart. This tissue calcifies and is replaced by bone, leading to lengthwise growth.
Height is very heritable - tall parents beget tall offspring - and “polygenic” - there are tons of genetic sequences that affect whether you are generally tall, average or short.
Some people carry genetic sequences that make their growth plates very active, meaning they will be generally taller. Others have lazy growth plates, making less new bone and limiting height. Lots of molecular stuff going on at these bone sites!
Height is also affected by environment. You need minerals like calcium to make new bone, so diet is important. Nutritional deficiencies and childhood disease can negatively affect bone growth.
Whether you inherit “tall genes”, “medium genes” or “short genes”, or however your particular combination averages out, is not a social construct. Importantly, both males and females are equally at the mercy of their height genes. When populations can access such things (economic investment, emigration, etc), average heights increase amongst both males and females.
But there is a third key input to height, and that is your sex. That is, when you compare males and females from the same demographic (same ethnicity/genetic pool, same socioeconomics), the males are alway taller. This is not a coincidence.
How does sex affect height? Let’s go back to those bone growth plates. When they are “open”, your bones are growing. This happens throughout childhood, and ramps up massively during puberty.
During puberty, growth plates activity increases under the control of hormones like growth factor hormones and sex hormones. Both estrogens in girls and testosterone in boys stimulate new bone growth. Now here’s the rub. Bone growth (and getting taller) stops when the growth plate “closes” (“epiphyseal closure”), and this is largely driven by only estrogens.
So what’s happening in girls? Well, around 10 yrs old, her body starts pumping out estrogen and she starts her growth spurt. A few years later, that estrogen closes down her growth plates and she stops growing. Females reach adult height around 14-15 yrs old.
https://t.co/enOE44e7pl
And compared to boys? Boys don’t enter puberty until a couple of years after girls. In those couple of years, they are growing in “childhood mode” - this is a couple of extra years that girls don’t get, and underpins a lot of the sex difference in height.
Then their testosterone kicks in, activating their growth plates and up they shoot (just like their female classmates did a couple of years ago). At around 16-18 yrs old, they convert enough of their testosterone to estrogens and their growth plates close, capping their height.
These differential growth trajectories between boys and girls are linked to sex. They are linked to the sex hormones made by the testes and ovaries, the interplay between these sex hormones, and how and when those sex hormones drive pubertal growth.
Even if a girl has inherited “tall genes” and drinks a ton of milk, her sex has an effect on her adult height. Even if a boy has inherited “short genes” and hates dairy, his sex has an effect on his adult height.
The effect of sex on your adult height is an outcome of your reproductive biology and the hormones associated with that reproductive biology. This is not a social construct, it is basic endocrinology.
And that’s what male sports advantage is - the acquisition of a physical trait that aids sports performance because one is male. Being male doesn’t mean you will be tall, it means you will be taller than if you had been female.
A follow up Q. The role of a Y chromosome gene in height is disputed. There is a sex chromosome gene (on both Xs and Ys) called SHOX, that is undeniably involved in height, in the sense that mutations cause bone growth disorders and short stature conditions. The possession of only one working copy has been proposed to underpin short stature in Turner syndrome.
However, typical height patterns in various DSDs can be explained by the hormonal interactions I describe above.
For example, Klinefelter males are unusually tall and have 3 SHOX copies. However, they also usually have low T, which delays puberty (longer childhood growth window) and delays the accumulation of sufficient estrogens to cap growth. Klinefelter males continue to grow long after other males have stopped (perhaps 20 yrs old).
In CAIS/Swyer, there is no T signalling and (usually) an absence of normally-timed estrogen supplementation. This delays puberty and lengthens the childhood growth window. Timing of diagnosis and estrogen supplementation will usually occur later than female growth is capped. So they are taller than female peers.
It's not a closed case, but I'm increasingly persuaded that hormonal milieu has sufficient explanatory power in most cases. The strongest counter is XX males, who are typically shorter than healthy males, but with the same T profile as Klinefelter males, so why aren't they also unusually tall?