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Doris Day and Rod Taylor face off in a scene from the 1965 movie Do Not Disturb.Photo by Camerique/Getty Images
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Last month in my Nautilus interview with love scientist Helen Fisher, we had a good time parrying over the value of viewing sex and romance in the pixels of a brain scan. Usually, she says, her friends and acquaintances, as well as journalists, want to talk about “the basics.” Just the other day, she says, “I spent a good deal of time with a person who is deeply attached to one woman and madly in love with another. He’s married to the first one, and was asking me how to solve their personal love problems. Those are the kinds of things people always ask me.”

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So Fisher, a biological anthropologist and Senior Research Fellow at the Kinsey Institute, and the chief scientific advisor to, welcomed the opportunity to debate her findings about the chemistry of love, and have some fun with me over my skepticism. In our previous interview, Fisher talked about the science behind her popular Nautilus essay, “Casual Sex May Be Improving America’s Marriages.” She discussed what we learn about each other between the sheets and just how underrated those benefits with friends can be. Our tete a tete below features questions and answers that didn’t make the cut the first time around, but which continue her insights into how people get stuck in the web of love.

You know, I meant to ask: What exactly do you mean by “casual sex”?

That’s a good question. Sex without any commitment is casual sex as far as I’m concerned. What’s it to you?

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I’m not sure there is such a thing as casual sex. Feelings always get crossed in some way.

Maybe I should say that.

Also, sometimes it’s just not right, is it?

You spend a lot of metabolic energy when you have sex. It’s also dangerous. You’re very close to somebody and they could stab you in the back. It’s also dangerous because you could fall in love. A friend of mine, Dr. Justin Garcia, did a study of one-night stands and hooking up. He asked various people why they went into it and 51 percent of both men and women said it was because they wanted to get to know the person better. So I do agree with you that casual sex is rarely casual. There’s some motive. Now there’s a lot of young men who might not agree with us. I’ve taken testosterone just to see what happens, and I understand the problems of teenage boys, and the bottom line is it’s entirely possible that some of them are into it just for the sex. But I think as you get older and you realize that sex is time-consuming, it’s energy consuming. You want to have sex with somebody you at least have a friendship with, or would like to make a friendship with. So, yes, I would guess that casual sex at least among people over 30 is never casual.

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What do you say to people who insist you should get to know somebody before having sex with her or him?

This is the most important question you ask. I’m not in the should business. I’m not in the business of telling anybody what to do. I’m not in the business of telling people that they should have casual sex and I’m not in the business of saying that they should not have casual sex. It’s not my game. I’m an anthropologist. How you do your particular partnership is your business, not mine.

So how do you know when to jump from casual sex to attachment?

I don’t think you ever know when to make that jump into attachment. I think the brain simply does this naturally. We’re built to form a deep attachment to another human being, to raise our babies. Forming a pair bond is a hallmark of the human animal. Ninety-seven percent of mammals do not pair up to rear their young, but people do. I had a girlfriend recently who said to me about her husband—she’s been married for over 50 years, very happily married—but she says, “Sometimes I hate him, but I always love him.” What she’s saying is that feeling of eternal deep attachment to another human being is easily felt over the long term.

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So let’s talk about the bonds of sex.

I don’t think sex is what bonds us. There’s much more than sex in a partnership. I mean there’s all kinds of people who have said to me that they’ve had better lovers than their husband, but they’ve never had somebody who was as funny, as smart, as kind, as good with the children, as productive around the home. There’s many reasons that you stay in a relationship. Sex may be an important one for some people and a very minor one for others.

Are the bonds of love just biochemical?

There’s biochemistry to everything—just like there’s math to everything, there’s physics to everything. Are you wondering which came first—the chicken or the egg? If that’s what you’re asking, that’s a metaphysical question, and I don’t know. But when you look at a person, do you get that feeling of romantic love and then fall in love with them?

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I guess I’m asking: In your view, are we just biological machines?

Well, I prefer to think not. But biology is always a part of it. I think there’s two basic parts of personality: There’s your temperament and your culture, your nurture, your environment. I’m an identical twin and we’re not exactly alike. No two people are alike. What’s really interesting, and the most important scientific thing in my lifetime, is an understanding of epigenetics. We are beginning to understand how the environment turns genes on and off and sends those on or off genes on to the next generation. We also know that your own biology is going to make some difference in whether you’re a Republican or a Democrat, what kind of person you choose to live with and marry, what kind of occupation you go into, so we’re all a giant combination of all of our biological mechanisms.

You categorize people into four temperaments: Explorer, Builder, Director, Negotiator. Based on questionnaires and brain scans, you correlate certain behaviors with brain systems and regions. But can you really draw a direct correlation between brain regions and behavior?

We’ve already done that and I’m not the only one that’s doing it. A most amazing moment for us was a study of people who were epileptics. They had the brain open, and every single time that they had an electrode stimulation to a very certain region of the cardiac nucleuses, which is part of this wanting system, the patient would turn around and say that he loved the doctor. So there are particular brain regions that seem to be directly associated with very particular emotions. We know the mirror neurons are linked with empathy. We know a brain region is linked with social norm conformity. We know certain brain regions are linked with math skills. Now of course you get into an environment where you’re not taught any math. You might be very good at shooting a squirrel in a tree in the middle of the Amazon, and you won’t know any higher math because you don’t live in a culture that enables you to express more of that brain system. We do know that some of these kids that play video games which are spatial are improving brain regions linked with spatial acuity. So some parts of the brain do appear to be related with very specific talents.

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Don’t you think there’s a personal danger to labeling yourself a type?

I bet you are a certain type that would ask that question. There’s some people who don’t want to be known and there’s other people who are dying to know more about who they are, and then say to their partner, this is the way I am, and if you want to reach me, talk to me the way I can hear you.

I don’t think it’s because I don’t want to be known. I just get uncomfortable being labeled a personality type. If I look at your four temperaments, I would say I’m all of them.

You are all of them. The issue is to what degree? Are you very good at math?

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I was when I was young. I guess I just let it slip away.

OK, because your skepticism is linked with the testosterone system, and some of your questions are indications of a high testosterone guy. You also have some of the facial characteristics of testosterone, so I think some of your skepticism comes straight out of your biology.

I guess I’m comfortable living with doubt. I don’t have to be defined.

Well, maybe you’re also comfortable not being curious about who you are.

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And so am I, by the way. I’ve never cared slightly who I am. I’m interested in who you are. I’ve never been to a psychiatrist. I’m just flat out not interested in who I am.

Sometimes I think that the more I read about neuroscience, the less convinced I am …

Less convinced about what?

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About the linear connection between neurochemistry and behavior. Aren’t brain processes nonlinear?

There’s no question about it. We do know that you can get the same printout, the same behavior from very different brain pathways. But the bottom line is we wouldn’t be able to all eat the same food and take many of the same drugs like aspirin or drink beer and have the same reaction. We share a great deal in common. We are the same species and there’s much in the brain that works in a relatively standard way, and we’re learning some of those standards, and we’re going to learn the exceptions. I mean, we all came from the same stock. You and I are brothers. It was a long time ago that you and I were sitting around a campfire in northern Africa and one day you and I decided we would go north, following the bison, and those of our friends decided they’d stick around, and sure enough we migrated into northern Europe; they stayed in Africa, but we’re pretty much the same.

If you examined the behavior of 100 people of the same temperament type, would you find the same neurobiology in them?

I think if you went into their brains, you would see different activity in the serotonin and dopamine systems from those two groups of people. Yes, I do think that there’s biology to behavior, and that this behavior can tell you something about biology. Yes, I do. Now, there’s going to be some behaviors that have nothing to do with biology. You grew up in a Muslim household and that’s what you learned, you’re going to be a Muslim. I don’t think that has to do with biology. If you grew up in a Christian household, you’re likely to be Christian. I don’t think that has to do with biology. I think it is your culture having to play a big role in what you believe. But whether you believe in god or do not believe in god, that’s probably biology. Whether you believe in this god or that god, that’s probably culture.

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Are you skeptical of any aspect of your work?

I lie in bed at night and I wonder what do I believe now that I won’t believe in five years? I think there’s only one thing that I hang on to: I want to believe that women are just as sexual as men. I know that men are just as romantic as women, I’ve proven that one. Most scientists studying sexuality are studying young college students because those are the ones that will answer their questions. It’s my hypothesis that in that particular time of life, the sexes are the most different. Testosterone is highest in men; estrogen is really quite high in women, and their reproductive strategies are quite different. Then as they get older, testosterone goes down in men, and testosterone becomes unmasked in women as estrogen goes down. You’ll see middle-aged men and women express their sexuality much more similarly. Then as you get into old age, it’s men that have the problems and often women who have the more stable sexuality. Now, we often measure sexuality in terms of how often you think about sex. Men think about sex more often. But what if you measured the sex drive with how many contractions you have during a sexual experience? You would say women are more sexually attuned. So I think we haven’t been asking the right questions. I don’t think we’re measuring the right population, and hopefully someday this thing that I’m clinging to, which might be wrong, might be right.

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