Sex Is Weird

Here's another fascinating post from Ed Yong at Not Exactly Rocket Science where he explains that, for birds, every single cell in their body is either male or female.

OK, that's interesting, but what's really weird, don't you think, is that it's not this way for mammals, including human beings? In us, it's our sex hormones that make us, physically, men or women. I don't know about you, but for me, the idea that something so fundamental to my self-image could so easily be entirely different is just... bizarre. Maybe I'd feel more comfortable if I were a chicken.

In an earlier post, Yong explained how silencing just one gene will turn ovaries into testes:

As embryos, our gonads aren't specific to either gender. Their default course is a female one, but they can be diverted through the action of a gene called SRY that sits on the Y chromosome. SRY activates another gene called Sox9, which sets off a chain reaction of flicked genetic switches. The result is that premature gonads develop into testes. Without SRY or Sox9, you get ovaries instead. 

But even that's not the weird thing. Apparently, this isn't just a matter of the developing embryo. Experiments have shown that silencing one particular gene even in adult mice will change ovaries into testes - within just three weeks. They won't actually produce sperm, but it's still really strange, don't you think?

The same genes may help to explain the frequent acts of gender-swapping among fish, reptiles and birds (no, Steve Connor, "one of the great dogmas of biology" is not that "gender is fixed from birth"). In these animals, oestrogens often cause males to change sex into females, and falling levels of oestrogen can trigger the reverse transformation. FOXL2 may also be involved. 

This is really fascinating, but when it comes to human beings, I don't know if I like the feeling that something so innate to my self-image could have been so easily subverted. Oh, sure, it's only chance that I got a y-chromosome anyway, but since I did, it's such a fundamental part of my entire being... (Of course, it still is, since my DNA is in every cell.) But y-chromosome or not, it would have taken just a very minor error to change me into a completely different person. Scary!

Sex is weird, isn't it?