Natural History Museum - scientists please!

[PenguindreamsofDraco]

I was there yesterday and wandered into the human biology section. Lots of sex, no gender, all good. Then I got to the bit on hormones and here I got confused.

It showed how XX and XY are the chromosomes and the baby gets one from each parent. There was a big pictorial flowchart on the wall showing how the genital ridge is formed a few weeks after conception. Then it said that at this point an XX genital ridge can turn into penis/testes and the XY genital ridge can turn into vulva etc.

It said if there were male sex hormones then the XX (or the XY)embryo would develop male characteristics and if there were no male sex hormones then the XX (or the XY) embryo would have female characteristics.

Scientists, what is this on about? The way the wall chart read (and it was covering an entire wall), irrespective of your chromosomes you could end up 'male' or 'female', it just depends on whether there are male sex hormones swilling around.

Are there really that many XX people wandering around with penises and testes? It honestly read to me from the wall as though it's pretty much 50/50 i.e. it's not your chromosomes that matter but the 'male sex hormones'.

Can someone explain this? My fear was that something very very rare is being presented as fairly common place, and I did rather wonder why that might be.

Thanks!

But I am pretty sure people like @ClairCAIS on Twitter do not say they are male but identify as female, nor that their sex is "intersex". They say that they are female.

They feel female because they and their families have believed they are female and they've been raised accordingly. That isn't always the case with people with people with intersex conditions. Sometimes they are uncomfortable with the sex they are raised as.

I think intersex people can choose their 'public' sex (or not choose if they prefer) but that doesn't change the essential biological truths. I don't understand how people can reject truths with regard to intersex conditions that they steadfastly and passionately hold on to in respect of transgender people.

It honestly read to me from the wall as though it's pretty much 50/50 i.e. it's not your chromosomes that matter but the 'male sex hormones'

The tissue that forms the upper genital tract is affected by chromosomes. It will form either the testes and genitalia round it, or it will form the ovaries and uterus and upper vagina. The part that is not needed is there early in development but disappears as this takes place.

The testes will then produce some testosterone. This will cause the tissue that will form the lower genital tract to form male genitalia. If this does not happen or there is a rare abnomality that affects the receptors (where the testosterone 'plugs in to') then female external genetalia and lower vaginal will form.

Sometimes it goes wrong, like other parts of the body go wrong in development. Once you have looked at genetics and development, you wonder how we are all here at all. But for some strange reason, if it involves genitals or sex, it seems to have deep cultural significance, require lots of whispering behind closed doors and a profound effect on the meaning of all life. Weird