The Period Brain: How Hormones Change Women’s Behaviour - Dr Sarah Hill - #992

**Chris Williamson** (0:00)
Two books on the vagina. Congratulations.

**Sarah Hill** (0:04)
I think it's a little bit more complex than that. I think it's a little more complex than that, but thank you.

**Chris Williamson** (0:09)
Why this one?

**Sarah Hill** (0:10)
Well, actually, it was the biologists in me that led me to this one. So the first book was really more about, I ended up in a rabbit hole because of my personal experiences with the pill. And this one, I ended up in a rabbit hole because I couldn't understand why women feel so terrible during the last two weeks of their cycle. And from an evolutionary perspective, it doesn't make a lot of sense for women to all have a disorder. Right? It just doesn't make any sense because generally, if there's some sort of a trait and it's causing problems, it'll get selected out of the population. And there's been all this really wonderful work that's been done in our field looking at the impact of estrogen and how when estrogen is high and rising across the cycle, that it does all of these really amazing functional things within the human, within women's brains and then with their behavior and everything else. But there's nothing like that about what goes on in the second half of the cycle. Instead, it just seems like women feel terrible. And so I was trying to understand why that is. So what is the deep evolutionary wisdom behind self-loathing that tends to go on during the second half of the cycle? And so why does it happen?
And is it supposed to? And is there some way that we can all feel better? So it was really sort of an evolutionary puzzle for me that I wanted to solve.

**Chris Williamson** (1:33)
Like crazy to think that that's for some, maybe even most women, 50% of their life.

**Sarah Hill** (1:39)
Yeah, it is. It's like 50% of your life. And it seems kind of crazy that, you know, that we would be designed in a way that we're supposed to be intentionally feeling bad. And so I thought there had to be something else going on, right? That it probably didn't make sense, that we're just supposed to feel terrible.

**Chris Williamson** (1:54)
What actually happens in the brain across the month?

**Sarah Hill** (1:58)
Well, so to introduce you to the cycle, we just have to understand that, you know, the whole purpose of having a cycle in the first place is reproduction. And for a male to reproduce, all you have to do is one thing, right? And that one thing is have sex. And for a female, it's a little bit more complicated than that, because we're mammals. And that means that we need to do two things in order to successfully reproduce, right? One is have sex. And that means doing things like attracting partners, being able to tell the difference between high quality and low quality partners, wanting to have sex, looking sexy, you know, smelling sexy, finding men sexy, et cetera, et cetera, et cetera. And there's a whole bunch of research that finds that, in fact, that that's true, right? And that all of those things tend to correlate to times in the cycle when estrogen is high and rising and egg is about to be released and sex can lead to conception, right? So that's job one for reproduction, if you're a human female. Job two is implantation in pregnancy, right? And so this is where a female body has to allow this foreign genetic material, half foreign genetic material, on this embryo implant, and then, of course, be able to carry it to term for nine months. And this is the set of activities that's coordinated by our other sex hormone, progesterone. And this is a sex hormone nobody talks about, right? It's like we think like estrogen, and then with guys, we think testosterone, and there's really not a whole lot of talk about progesterone. And so I was kind of curious about like what actually goes on during the point in the cycle when progesterone is the dominant hormone, right? Are these things actually trying to guide our brain and behavior in a way that will help to facilitate pregnancy, right? Because we find that, you know, human like women are become very much oriented toward men and towards sex in the first half of the cycle when estrogen is high and rising. And so I was really trying to figure out like, is there some method to our madness, right, during the second half of the cycle when progesterone is dominant? And might it be creating shifts in the way that we feel and experience the world that might be functional? And might they feel a little bit dysfunctional just simply because we don't really give voice to them?