Most Replayed Moment: Would You Still Love Them If You Came Off The Pill...? Your Hormones Are Controlling You!

Steven Bartlett (0:01)

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Dr Sarah Hill (0:36)

Yeah.

Steven Bartlett (0:37)

So throughout a woman's 28-day cycle, does she always want a nice guy?

Dr Sarah Hill (0:42)

No. So women's partner preferences and the types of qualities that women tend to prioritize in their choice of partners do change across the menstrual cycle. And this changes with our sex hormones. So during the early part of the menstrual cycle, both sets of sex hormones, so our estrogen and progesterone, which is our second primary sex hormone, they are low. And then as estrogen begins to increase, which is something that happens as eggs start to mature in the ovary, and as the eggs are maturing, they release estrogen. And as an egg, as a dominant egg is chosen and begins to fully mature, so that way it will be released at ovulation.

Steven Bartlett (1:25)

Which is how many days in to the cycle?

Dr Sarah Hill (1:27)

Usually, estrogen really starts to surge right around day nine of the cycle, but it really hits its high point usually right around day 14, which is when ovulation occurs. So estrogen begins rising sharply around day nine of the cycle. And again, the first day of the menstrual cycle is the day that your period arrives. So that's day one, about day nine, so about a week and a half after your period started. Most women will start to have a pretty dramatic increase in estrogen, estrogen will climb, climb, climb, climb. It will peak around day 14, which is when ovulation occurs. And this is when an egg, of course, is released, and pregnancy is possible from sex.

Steven Bartlett (2:10)

So from day nine till day 15?

Dr Sarah Hill (2:12)

Till day, yeah, till day 15 Day nine to day 15 are usually, like that's usually when we sort of bookend the fertile window. And during this time, not surprisingly, women experience a change in their sexual psychology, right? So women become increasingly attuned to all things sex. So what we tend to see is that women's sexual desire increases right around that time in the cycle. Women have more sex during that time in the cycle. Women masturbate more during that time in the cycle. And women become more exacting about who it is that they desire as a romantic partner or a sex partner.

And in particular, what we tend to see is that as estrogen is increasing across the cycle, so too does women's interest in cues that historically have been related to high genetic quality or genetic compatibility within their choice of partners. So two of the traits that we know to be particularly pronounced in terms of women's interest near high fertility in the cycle are cues related to testosterone and masculinity. And the reason for this one is because testosterone is a known immuno-suppressive, meaning that it has the effect of suppressing the immune system. And so people who have relatively high levels of testosterone, this is a cue that their bodies are in such good physical condition, right? Their immune system is so strong and robust that it can handle being suppressed by testosterone. So people who have higher testosterone are believed to have greater immuno-competence relative to people with lower levels of testosterone. And what we tend to see is that lo and behold, during that peak fertility time in the menstrual cycle when estrogen is high, that women exhibit a greater preference for cues related to testosterone in men. So we find, for example, that women desire more masculinized male faces, voices, and behavior at high fertility in the cycle compared to low fertility in the cycle.

Steven Bartlett (4:22)

How do you test this?

Dr Sarah Hill (4:23)

You test this by looking at what it is that women are looking for, and you look at it over time. So just to give you an example of one of the sort of most robust studies that's been done looking at this phenomenon. Researchers had a group of women bring home a bunch of little plastic tubes in a freezer bag, and they had them spit into these little saliva collection tubes every day of the cycle across two menstrual cycles. On those same days when women were taking a saliva sample, they were also evaluating the attractiveness of male faces. And the thing that the women didn't know is that the researchers knew the testosterone levels of the faces of the men that they had them looking at. Because the researchers had men come into the research lab beforehand and took their morning testosterone levels over the course of several days to get an average morning testosterone level for these men. And so when they got all the saliva samples from the women, they assayed all of their saliva and they were able to look at women's estrogen changes across the cycle and then how it related to their facial preferences for men. And what they found was first that of course estrogen tended to increase and peak during this fertile window. So days nine or so to day 15, women's estrogen levels were high and during this time what they also found is that women's preference for testosterone levels in the faces of the men they preferred also increased. And so there was this really beautiful overlap between women's estrogen levels and their preference for testosterone going to show that estrogen loves testosterone, right? So women during this estrogenic phase in the cycle have a heighten preference for cues related to facial masculinity. They also have a greater preference for vocal masculinity. So women at high fertility in the cycle also like the sound of more masculinized male voices. They tend to like more social dominance in terms of behavior relative to what we tend to see when women are at low fertility in the cycle.