preference for the smell of a fertile female over the smell of an infertile female or even of another male. It requires a sexy (i.e., copulatory) experience to teach the male rat’s brain that a female in estrus is “sexually relevant.” The instinct to attempt copulation is there, and he’ll attempt copulation with everybody—but if he doesn’t have the experience, he can’t learn how to turn that instinct into successful action.
What is innate is the mechanism by which this learning takes place: ratty SIS and SES and the ability to learn through experience and association. But rats need experience to teach their SIS and SES what’s a threat and what’s sexually relevant.
In a rat’s natural environment, outside the lab, he would never need a jacket in order to feel sexy, and the smell of lemons wouldn’t make him ejaculate. The rats learned these things because humans created an environment where those were salient features of their sexual environment. But even things you would assume are innate—fertile female rats—must be learned by experience.
“Years of struggle.”
That’s how Merritt described her sex life. After she graduated, we became friends, which is when she told me that the most important thing she had taken away from my class was that there is a brake, as well as an accelerator. It helped her understand why she felt desire for sex . . . but it seemed to be trapped. She realized she had a sensitive brake: Things had to be “just right” for her to get aroused, and she needed total trust in her partner. And she worried about sex while she was having it. She called this “noisy brain.”
“Yep, totally high SIS. The noise is your sexual brakes, metaphorically squealing,” I said. “It would explain the ‘windmilling on a cliff’ sensation you described to me a million years ago—your accelerator and your brakes are activated at the same time.”
With sensitive brakes, Merritt’s sexual motivation system is the highest risk for problems with desire, arousal, and orgasm—and she had struggled with all three at some point in her life, she told me. Lately, it was orgasm.
“I can get so close, and then it’s like there’s all this noise in my head.”
She has a great relationship, she and her partner have loving and playful sex on a pretty regular basis, but her arousal bottlenecks inside her and then orgasm just isn’t there for her, and then she gets frustrated, and basically sex is turning into more of a hassle than a pleasure. We’ll hear more about the cause of Merritt’s challenge in chapter 4, and a great deal about the solution in chapter 8.
all the same parts, organized in different ways
It’s true for us, too. Humans go through a learning process similar to (though much more complex than) rats. And that learning process is different depending on whether you’re a boy or a girl. There are several theories about how this works, but I’m going to tell you the one I like best.
Let’s imagine those fraternal twins from chapter 1, the brother and sister. Born on the same day, having developed in the same hormonal environment in the womb, they’re as similar as different-sex siblings can be.
The little boy—let’s call him Frankie—soon begins to notice (in his preverbal infant way) that some significant changes happen to part of his body—his penis grows and changes and feel tingly! His infant brain begins to link that change in his body to the external stimuli in the environment and to the internal sensations and emotions that accompany it. And so from the earliest moment, his brain is linking his environment with his erections. In boys, then, the process of teaching their accelerator what constitutes a sexually relevant stimulus is a fairly straightforward processof categorizing as “sexy” those things that are associated with erection. 13
The little girl—we’ll call her Frannie—doesn’t have that obligingly obvious physiological response to her