Dr. Helen Fisher, Ph.D., Biological Anthropologist, is Senior Research Fellow at The Kinsey Institute and Chief Science Advisor to Match.com. She is a leading expert and highly referenced scholar on the science of lust, romance, and attraction, having written six books on these topics, now sold in 22 countries. Dr. Fisher appears regularly on national and international TV, radio, print, and podcasts, notably a TED All-Star with over 21 million views of her TED talks.  She is the co-founder of this website, www.theanatomyoflove.com.

Eds: On the topic of infidelity, what is the question that interests you the most?

Helen Fisher: The single most interesting piece of data that I've ever found came out of an academic paper in 1985. The scientists reported that 56% of men and 34% of women in their study were unfaithful to their partner, yet they were in long-term happy partnerships. That's a revealing data point. Apparently, people sleep around—even when they are in really happy relationships. It made me wonder whether humanity has evolved a predisposition to philander for Darwinian evolutionary reasons. Psychologists have dozens of theories about why people cheat. Boredom; poor communication; relationship dissatisfaction; opportunity; to solve a sex problem or have more sex; to feel more appreciated; for adventure; due to issues in their childhood; or feelings of entitlement (as when one partner makes more money, is better looking, or has a better education or background), or just because they want to get caught and terminate their relationship: there are hundreds of reasons that people say they are unfaithful.

"… adultery is so prevalent everywhere in the world."

But this doesn't explain why happily partnered people cheat and why adultery is so prevalent everywhere in the world—from those in hunter-gathering cultures to those who farm, herd, or live in postindustrial societies. Psychologists offer all kinds of cultural and psychological reasons for philandering. They're all good. But could there be an underlying biological component as well? That's what interests me.

Eds: In your book, Anatomy of Love, you note that after reading 42 ethnographies on people's past and present, "adultery occurred in every culture…There exists no culture in which adultery is unknown; no cultural device or code that extinguishes philandering" (p. 70). In your estimation, what is your best guess as to why infidelity is so ubiquitous that it transcends cultural customs, even time itself?

Helen Fisher: Let's dial back 300,000 years after the modern human brain had evolved. You have one man and one woman. They fall in love. They form an attachment and live in a little hunting and gathering community of about 25 individuals. They have two children. Occasionally, the man goes walking, visits his brother in a different hunting and gathering band, meets a woman there, and begins to have sex with her--producing two more children. From a Darwinian perspective, he will, by being unfaithful, double the amount of DNA he sends into the next generation. For him, cheating was adaptive.

"…why would a woman be unfaithful?"

But why would a woman be unfaithful? A lot of people think that women are less likely to philander. But this doesn't make sense. Generally speaking, every time a man sleeps around, he's sleeping with a woman. So, either a few women are sleeping with a lot of men, or a lot of women cheat. And in reading a host of ethnographies, it appears that women are just as adulterous as men.

"…what would the payoffs be?"

But what would the payoffs be? Well, some will get pregnant, creating more variety in their lineage. This would be adaptive: the extra child might have better eyesight than her other children, be more charismatic, or simply be better at hunting Buffalo. With adultery, women (like men) would have produced a greater variety of offspring, some of whom might live through difficult times, passing their mother's DNA into the future. Adultery had this payoff for ancestral women too. But there would have been other genetic perks for ancestral women. For example, if her husband was eaten by a lion, slipped and disappeared into a cave, and was never seen again, she might have an insurance policy—a paramour who might step in to help her parent her offspring. Adulterous women would also have more support when they traveled to different communities. In her book, Nisa: The Life and Words of a Kung! Woman author Marjorie Shostak writes about the Bushman woman of the Kalahari Desert in Botswana, whom she explains has many lovers;  she states, "There are many kinds of work a woman has to do, and she should have lovers wherever she goes. If she goes somewhere to visit and is alone, then someone there will give her beads, someone else will give her meat, and someone else will give her other food" (p. 271).3 For millions of years, those men and women who slept around had more children who survived to adulthood to have more offspring themselves, passing on this predisposition for adultery we see today. This way, humanity evolved what I call a dual human reproductive strategy—a tremendous desire to fall in love, form a partnership, and rear their children as a team....and also sleep around. "But the sheer prevalence of worldwide philandering…suggests that humanity has evolved this dual reproductive strategy: to love and attach to one and cheat with others." This isn't to say that we are driven to cheat. Not at all. We've evolved a huge cerebral cortex with which we make decisions. Many say "no" to adultery.

But the sheer prevalence of worldwide philandering, even among happy partners, suggests that humanity has evolved this dual reproductive strategy: to love and attach to one and cheat with others—a primordial adaptive mechanism to make babies that have babies and send our DNA into tomorrow with a variety of partners.

Eds: Clinicians struggle with this question: why do people in happy unions stray? Do you attribute the dual reproductive strategy to that outcome?

Helen Fisher: It's probably an underlying cause. If you ask happily partnered people why they stray, they'll say, "I don't know;" "I was drunk at the Christmas party;" "I get lonely when my partner travels;" or "my partner is not that great in bed." They're going to give you any one of myriad psychological reasons. All are true. But what's important to remember is that those psychological explanations are driven by a primordial and unconscious drive to send one's DNA into tomorrow. For millions of years, those who had babies by more than one person created more genetic variety among their young. In times of real environmental change, some would live—passing this predisposition for adultery to humanity today. Once again, over 50% of Americans today do not sleep around. They might say, "I lust in my heart for somebody in the office or my social circle, but I've never followed through."

Eds: Based on your work, what do you think clinicians need to know about the treatment of infidelity? How can they translate this anthropological information into their work with couples?

Helen Fisher: That's the essential question, of course. I'll tell you a story that may be of use. Years ago, I was in the green room at the Oprah Winfrey show in Chicago. I was preparing to be on set with a young woman whose husband had been cheating. They put me in a separate green room from her because, as the producer explained it to me, the woman might feel that I was trying to excuse her husband's adultery with my underlying biological explanation for philandering. Hence, she might hate me. Ok, I said. But as I was sitting in the green room sipping coffee, in sneaks the woman from the other green room. I recall her saying, "Dr. Fisher, I just want to tell you how helpful it has been for me to know that my husband's philandering isn't my fault. He didn't sleep with somebody else because he didn't love me. He did it for an evolutionary reason. This mess is not just about me. You've really helped me.

"…in that moment, I realized that my information could help people understand more about a philandering partner. Mother Nature is a nasty old witch, leaving some of us with an inclination for adultery. Some succumb."

My evolutionary explanation for adultery doesn't excuse her husband's behavior. He made this decision. But, in that moment, I realized that my information could help people understand more about a philandering partner. Mother Nature is a nasty old witch, leaving some of us with an inclination for adultery. Some succumb.

Eds: That makes a lot of sense, and you're absolutely right—you're not going to take away the sense of betrayal. But one of the lingering questions that folks often have is why? Why did they do it? Why did it happen? And many times, the partner who had an affair will say, "I don't know, it just happened, I got drunk, etc." So, maybe offering an evolutionary perspective and saying, "Let's take it away from the two of you and broaden it out to millions of years of human evolution." This may allow the hurt partner to go, "maybe it wasn't just me." So, although other systemic issues within the relationship undoubtedly existed, this issue also exists, perhaps even tipping the balance toward philandering.

Helen Fisher: Indeed, scientists now know some of the genetics that may underly the predisposition to cheat. In a fascinating study by Walum et al. (2008), a group of scientists studied a particular gene in the vasopressin system in 552 married men. Individuals had inherited either no copies, one copy, or two copies of this gene. These scientists weren't studying adultery. But those men with more copies of this gene were also more likely to score lower on a questionnaire measuring "partner bonding," more likely to have had a marital crisis in the past year, and more likely to score lower on scales of marital satisfaction. It's parsimonious to suggest that this gene might also predispose one to philandering. In fact, a gene in the dopamine system has been correlated with infidelity. Those with this gene were more likely to philander. "We aren't built to accept adultery in a partner easily." Of course, along with adultery, our forebears also evolved a host of other feelings to guard against philandering: guilt, jealousy, shame, feelings of abandonment, possessive anger, and much more. People who have been sexually betrayed don't take the experience lightly. Even when they forgive, they rarely forget. They have been threatened in a profoundly fundamental way. They could have lost their partner—a co-parent, as well as money, property, and even their children. We aren't built to accept adultery in a partner easily.

Eds: In your work, you've also noted that some medications can elevate the pain of rejected love. For instance, you've dubbed some antidepressants as "a vaccine against love" (p. 216).2 What role, if any, do you think medications play in the emergence of affairs? 

Helen Fisher: There are many kinds of medications, of course. But the ones most often used throughout America are serotonin boosters or SSRIs, including Prozac, Paxil, Lexapro, and others. These drugs upregulate the serotonin system in the brain. And increasing serotonin activity often has a negative correlation with dopamine; it suppresses dopamine activity, regularly blunting emotions. Some people really need these drugs to get out of bed in the morning or curb their desire to harm themselves. I'm not referring to these individuals. But, about 73% of people who take these drugs don't really need them long term.6 They take them to solve a particular issue. But after their problem has been solved, they keep taking them—continuing to blunt their affect and emotions. And these SSRIs can jeopardize sex drive and sexual performance, as well as dampen feelings of romantic love and attachment. I get letters from people all the time, trying to make sense of this. For example, I got an email recently from a man who told me that he was still madly in love with his wife, and until recently, she had been crazy about him too. They had been married for 11 years, with two boys, ages five and seven. But recently, his wife went back to school; she wasn't doing well, and a doctor put her on an SSRI antidepressant. Three months later, she asked her husband for a divorce, saying that she felt nothing for him anymore. I've probably gotten over a hundred letters like this. I received a particularly touching letter from an MD from Plano, Texas. As I recall him saying, "I suffer from severe depression. It comes in bouts. And the last time I took one of these SSRIs, it really lifted the depression. But I also began to think that I no longer loved my wife and needed to leave. I heard you speak at the annual meeting of the American Psychiatric Association, and I suddenly realized that the drugs were creating my disinterest in my wife and family. I stopped taking the drugs and am back in my happy marriage. And for me, next time I have one of these severe depressions, I'm just going to go through the depression. My family is too important to me." Interestingly, I also got a letter from a man who planned to use an SSRI to dampen love! He said that he loved his wife and children. He didn't want to leave them. Yet he was having an affair with another woman. So, he decided to take an antidepressant to 'kill the romance' with his extra lover. These drugs appear to be useful in several ways. But I hypothesize that you can jeopardize your partnership if you take these drugs long-term.

Eds: This is a huge problem, so much so that roughly 80% of psychiatric medication prescriptions are written by general practitioners. They're not even written by psychiatrists anymore. So, your hypothesis is important not only for medical professionals to know but also for couple's therapists. "I'd like clinicians to know that although these drugs can be good for several short-term purposes, they can have unexpected long-term consequences."

Helen Fisher: Yes. I'd like clinicians to know that although these drugs can be good for several short-term purposes, they can have unexpected long-term consequences. If I were a clinician, I'd 5 tell my patients that humanity has evolved three highly specific brain systems for mating and reproduction: the sex drive; feelings of intense romantic love; and feelings of deep attachment. And I'd say that if a patient wanted to remain taking an SSRI long term, they may risk blunting any or all three of these basic brain systems. Actually, I'm doing an fMRI brain scanning experiment right now, trying to establish how these drugs alter one's feelings for a partner.

Eds: Another related issue is the expectations and pressures of modern romantic relationships. Eli Finkel writes of the "all-or-nothing" marriage,8 espousing that today there is a lot of pressure put on the primary romantic relationship—not just to be a companion but also to help selfactualize the other person. What do you think about this idea? Do couples put an undue burden on their partner to fulfill all their needs (including self-actualization)? "…we put too much pressure on our primary partnership these days. This pressure isn't natural."

Helen Fisher: I certainly agree that we put too much pressure on our primary partnership these days. This pressure isn't natural. For millions of years, our forebears lived in little hunting and gathering bands of about 25 people; some 10-12 were children, the rest were adults, probably about two married couples and their kin. But these forebears lived in extended family groups— with a lot of "helpers at the nest." If a baby started crying and the mother was busy with other matters, she could pass her infant to her sister, aunt, cousin, etc. In today's largely postindustrial world, we live in small 'nuclear' families, often not surrounded by extended kin. This new family configuration certainly puts more pressure on couples to be just about everything to their partner. "…today, we live in an era when couples can build the kind of partnership that suits them." On the other hand, today, a great many couples are building the kind of partnerships they want. For example, I got married two years ago, and we're LAT, "Living Apart Together." I have kept my two-room apartment in New York, and my husband lives in a bigger apartment in the Bronx. We spend a couple nights a week in these separate homes, as I like to go to the theater with girlfriends, and he likes to read all evening. And it's always exciting when we get back together. This isn't possible for everyone; not everyone would even enjoy this living arrangement. But today, we live in an era when couples can build the kind of partnership that suits them. In fact, I think Tolstoy got it wrong when he wrote, "All happy families are alike; each unhappy family is unhappy in its own way." I suspect it's the reverse. Bad marriages are bad for some very basic reasons, whereas good marriages are good in complicated and unique ways. Today we live in a world where you can make the kind of partnership that works for you. We're not all stuck in the 'all-or-nothing' dynamic.

Eds: Absolutely! As you're often talking about changing relationship structures over the decades (i.e., women gaining traction with entering the workforce), we have noticed a rise in infidelity prevalence rates, particularly since the pandemic. What role do you believe this has on the future of adultery if any?

"…Perhaps video chatting will initiate partnerships that are more intimate and less susceptible to philandering."

Helen Fisher: Foremost, it's exceedingly difficult to collect honest data on adultery. People define adultery differently. In fact, today, academics believe there are three basic forms of adultery: sexual adultery—in which partners have a sexual relationship with no romance; romantic adultery—in which a couple has romantic passion but no sex; and relationships in which both sex and romance are involved. But I'm not convinced that people are more promiscuous today than before the pandemic. I mention this because I do an annual study with Match.com called "Singles in America." Every year since 2010, my colleagues and I have created a survey with about 200 questions, collecting data on a sample of 5,000+ singles using a national representative sample based on the U.S. census. We don't poll Match members, and we now have data on over 60,000 American singles. Most interesting, the pandemic has clearly led to what I call "post-traumatic growth." For example, in 2019, we asked participants the question: "Would you like to meet someone who wants to marry?" 58% responded, "yes." But in 2022, 74% of singles replied "yes." In fact, in 2021, after Americans were released from lockdown, the press was anticipating what they called a "slutty summer." It didn't happen.

"Adultery will always be part of society…[but] I'd say that Cupid beat COVID."

All our data suggest that today's singles have become dedicated to finding a long-term, committed partner. And I've read that a lot of wedded people have come out of the pandemic with stronger marriages as well. Adultery will always be part of society, but I don't see any real evidence that this pandemic produced a huge rise in philandering. In fact, I'd say that Cupid beat COVID. Another current courtship pattern may contribute to a reduced frequency of adultery—what I call "slow love." Fifty years ago, the vast majority of men and women married in their early twenties. Now they're marrying in their late twenties and early thirties. This is a dramatic and important shift in courtship patterns. I say this because I've studied divorce in 82 cultures (between 1947 and 2011) through the demographic yearbooks of the United Nations. And, around the world, the later you wed, the more likely you are to remain together. Supporting this pattern: in a study of 3,000 Americans, researchers found that those who married after a year of courtship were 20% less likely to divorce (than those who married during the first year of courting); moreover, people who married after three or more years of courtship were 39% less likely to divorce, with longer courtship leading to later marriage and less divorce. Later marriage may not curb infidelity among those who decide to pursue it. Nevertheless, due to this long pre-commitment courtship stage, more singles may have their flings before they wed— ushering in a few decades of relative family stability.  "Sure, some people are likely to be more predisposed to adultery than others; but many of us will forgo philandering for a host of cultural (and biological) reasons." Perhaps most important to this discussion: Just because we live in a world where people have lots of opportunities to cheat, it doesn't necessarily mean that they will turn into rabbits—and race to philander. It's not the way the brain works. As we grow up, we build a host of values, goals, and experiences. People override their primitive drives to meet their objectives all the time.  Another thing that may contribute to less adultery is the rise of video chatting before the first date. In our 2015 Singles in America sample of 5,000+ singles, 6% of singles did a video chat before meeting in person. In 2020, 19% of singles did a video chat before meeting in person. And in 2022, 25% did a video chat before the first date, and 37% were open to it.11 More and more singles are meeting first on the Internet, in real-time. Moreover, over 63% of singles reported in 2021 that they were having more meaningful conversations during these video conversations. More than 50% also said they expressed more honesty, transparency, and self-disclosure during these meetings, and they cared somewhat less about a potential partner's looks and were more interested in whether a prospective partner was fully employed and financially stable. Perhaps most importantly, 92% of singles today wanted a partner with "emotional maturity." This is probably a reach, but perhaps video chatting will initiate partnerships that are more intimate and less susceptible to philandering.

Eds: Interesting. So, you study the biological aspects of personality (i.e., temperament). And using fMRI brain scanning, you have established that humanity has evolved four foundational styles of thinking and behaving linked with the brain's dopamine, serotonin, testosterone, and estrogen systems. And you have coined these temperament styles the Explorer, Builder, Negotiator, and Director. Have you found any patterns or correlations between these four basic personality styles and one's proclivity towards infidelity?

"…if an individual expresses many of the traits of the serotonin system, including the predisposition to be loyal, and also believes that sex is less important to a successful relationship, perhaps they may also be predisposed to engage in less philandering."

Helen Fisher: I have only some preliminary data and some hypotheses. Some 15 million people in 40 countries have now taken my biology-based personality test, the Fisher Temperament Inventory. It is the only personality questionnaire validated by brain scanning. And of this population, I studied the attitudes of 40,000 American singles. Included were correlations with five variables: gender; level of education; religious preference; political orientation; and the degree to which an individual regards sex as essential to a successful relationship.  I found that men and women who were very expressive of the traits linked with the serotonin system in the brain, whom I call Builders, regarded sex as significantly less essential to the success of a relationship. Those who are highly expressive of the traits in the serotonin system also tend to be traditional, conventional, rule-following, respectful of authority, detail-oriented, conscientious, loyal, and religious. Religious people don't tend to be any less adulterous. Nevertheless, if an individual expresses many of the traits of the serotonin system, including the predisposition to be loyal, and also believes that sex is less important to a successful relationship, perhaps they may also be predisposed to engage in less philandering. On the other hand, perhaps people who are highly expressive of the traits linked with the dopamine system in the brain, whom I call Explorers, are more inclined to be adulterous: Dopamine has been linked with a suite of specific traits of temperament, including novelty-seeking, risk-taking, curiosity, creativity, impulsivity, energy and the belief that sex is an essential part of a successful partnership. This doesn't necessarily mean that these individuals will also be adulterous. They may be drawn to exploring in other ways, such as reading widely, hiking, going to the opera, theater, and/or symphony, traveling widely or taking illicit drugs. But, they may be more predisposed to get themselves into situations that lead to philandering. We all express some of the traits in all four of these foundational brain systems. Then, upon this brain wiring, our childhood and adult experiences shape and drive our behaviors in numberless complex ways. So, to understand the full relationship between basic temperament and promiscuity, one would need to have a large sample of individuals take my personality test and crosstab their results from this test with their results on a host of other questionnaires that assess their sexual attitudes and behaviors. One of these studies has begun. A group of medical scientists in Sweden is currently studying sexually transmitted diseases, and they administered my questionnaire to 221 patients in their medical clinic. They found that people who came into their clinic with various sexually transmitted diseases (STDs) were also statistically significantly more likely to express the traits linked with the dopamine system in the brain. They were predominantly Explorers—risk-taking, novelty-seeking, impulsive, and curious. Most likely, not all of these people with STDs were adulterous; but it's a good bet that some were.

"But here's the problem: These three basic brain systems don't always work together."

Eds: Interesting. So, going to the neuroscience side of things again, is there any new information on the role of the brain/neuroscience related to infidelity? 

Helen Fisher: I have found that three different foundational brain systems evolved for mating and reproduction: the sex drive; feelings of intense romantic love; and feelings of deep attachment. The sex drive most likely evolved to drive our forebears to seek sex with a range of partners; feelings of intense romantic love probably evolved to enable our forebears to focus their mating energy on a single individual at a time; and feelings of deep attachment probably predisposed individuals to form a partnership and rear their offspring as a team.

"We can say no to adultery. Many do."

But here's the problem: These three basic brain systems don't always work together. You can lie in bed at night and swing from feelings of deep attachment for one person into feelings of intense romantic passion for another, then on to some sexual feelings for a third. We want to feel all three for our partner. But these loosely linked brain systems enable us to feel deep attachment for one partner while we feel romantic passion and/or the sex drive for another. Once again, however, we have also evolved a huge cerebral cortex with factories and pathways that enable us to make decisions. We can say no to adultery. Many do.

Eds: That's well put! Last question—suppose you had access to any technology (invented or not yet invented) and ready access to couples; what are the "burning questions" that still need answering related to coupling, relationships, and specifically infidelity?

"I think I would begin to understand a huge number of things about how to help them and why they seek what poet Lord Byron called "fresh features."

Helen Fisher: Well, I would love to have a very pretty bonnet or baseball cap that a client could wear—one that recorded all neural activity while they interacted with their spouse or partner, minute by minute. I think I would begin to understand a huge number of things about how to help them and why they seek what poet Lord Byron called "fresh features."

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