The Science Behind How Men and Women Fall in Love Differently

In this compelling episode, we sit down with Dr. Joe Malone, a sexual integrity scientist and expert in human biology, to explore the biological and chemical differences between men and women—especially in how men and women fall in love and bond.

Drawing from cutting-edge science and knowledge of pair bonding in humans, Dr. Malone explains how hormones like vasopressin and oxytocin shape male and female attachment, why casual sex impacts men and women differently, and how the Catholic view of sexuality aligns with modern biology.

What you’ll learn in this episode:

Resources:

Transcript:

Colleen: Hello and welcome to the Living a Culture of Life podcast by Human Life International. I’m your host, Colleen, and I’m joined today by Dr. Joe Malone. Welcome!

Dr. Joe Malone: Thank you! I appreciate your ability to have me on and the honor of being here. Thank you.

Colleen: I’m really excited for this conversation today because we’re going to be talking about the biological sex differences between men and women, and how men and women fall in love differently. So, you’re a—what’s the official phrase—sexual integrity scientist? What is that? I’ve never heard that phrase before. Can you explain a little bit about what that actually is?

Dr. Joe Malone: Yes, I’m a rare breed, I guess you’d say. I’m the only person that I know of actually in academia like me. So, basically, I came to this through a series of—I think—providential happenings in my life. I didn’t ever intend to end up here.

But I created, at the university I was teaching at in Tennessee—Middle Tennessee State—I created a women’s wellness program there, and a class that I specifically taught called Women’s Personal Conditioning. And I was doing research for the PhD I got, and among the research that I was doing—on things like exercise effects, their ability to get exercise on campus, and their ability to get good nutrition on campus—this theme arose that I was really not expecting.

It had to do with a thing called hookup culture, and it didn’t take me very long. Among the interviews—I did 32 in-depth interviews with them and 10 focus groups, all women’s class focus groups—I saw right away that this casual sex, which is what they were describing, and the avoidance of relationships, although most of them wanted to have relationships… well, the males didn’t. And I could see that it was much more destructive to the women than what I had originally set out to do.

So I went to my committee and asked them if I could switch in the direction of sexual wellness, rather than just overall young women’s wellness. And they said just what you said, Colleen—they said, “We don’t know if anybody else is doing anything like this, so yeah, we think that would be a great idea.”

As I went along, I got the PhD. I ended up getting canceled at this university because I was unaware that I was ruffling feathers by saying things like “males and females are physiologically different.” And again, I had all the proof, because I was researching it this whole time.

But in the process of all this—writing the book that I eventually published, which again, had switched from an overall wellness focus to young women’s sexual wellness—I realized that sexual wellness, when you really took all the research and sifted it down, parsed it all out, really equaled sexual integrity. Because sexual integrity is the way we’re designed.

And I didn’t come to that conclusion because I was a Christian. I specifically went into my research with the thought process of, “I’m going to find the best research, find the authentic research—mostly natural science-based research, and some social science—and I’m going to write the book and teach people and speak on this, telling them the truth.”

So, it turned out that even though it’s—as we’re going to see today—a difficult journey sometimes to get on the pathway to traditional courtship, traditional marriage, traditional family, it is actually the optimal human condition. So I’ll say it again: what I’ve discovered is sexual wellness is sexual integrity.

What is “Sexual Wellness” and “Sexual Integrity”?

Colleen: What do you mean by both those terms? Like, I hear that and I kind of generally know what you mean, but I don’t know exactly. Like, what is sexual integrity? Is that just picking one partner for life? And is the wellness health wellness, or is it emotional as well? What does that look like?

Dr. Joe Malone: Good questions. It’s all—wellness is all of it, really. Wellness is the big picture. Another good word for it would be well-being. So it could include the physical, the social, the emotional, the interpersonal—all of it.

And integrity—the best way I think to paint the picture of integrity, as far as sexual integrity is concerned—and this is what I came upon… So originally, not long ago, I was a Protestant. But what drew me to the Catholic Church was the Catholic teaching on sexuality. Because when I did the research, and then God brought different manifestations of Catholicism into my life—again, I wasn’t planning on this—but these various people…

For instance, I went up and spoke at Princeton to a group called The Love and Fidelity Network, which started there in 2007. It began because one of the undergraduates got tired of hookup culture being the only option on campus. That movement rapidly spread to other Ivy League campuses—Notre Dame, Stanford, etc.

The people up there, in 2018, read my book and asked me to come speak at their conference. I was glad to do that. And when I got up there, on the surface, they’re a non-denominational, non-religious group. But really, what I found out was—they were primarily Catholic. A Catholic group.

From there, people asked me to go to Catholic University of America to speak next. So I spoke there in the spring. And there was a gentleman there named Dr. Pat Fagan, who is one of the luminaries, I found out, in the Catholic world. My wife Jody and I had an afternoon in a pub on campus with him, and he ended up explaining all of the different things that I eventually found out mapped on so well to the Catholic teachings.

As far as human sexuality goes, it mapped on so well to what my research was showing—physiologically—that it showed me that basically the Catholic teaching on sexuality had said all these years—with God working through them—really was the ideal approach to sexuality.

Let me give you an example, because I can tell you’re wanting an example. This is something I was thinking about talking about later, but let’s just bring it right up: women’s sexual behavior.

Okay, young women’s sexual behavior affects their future health. Now, what do I mean by that? So here’s the tie-in between integrity and wellness: Early promiscuity leads directly to higher chances of vaginal and cervical cancer, for one thing. Having none or minimal number of pregnancies—and none or minimal breastfeeding—raises her lifetime chances of developing ovarian and uterine cancer.

So these are very specific things. Very specific behaviors that raise risk down the line. Delayed childbearing and fewer pregnancies raise the risk of lifetime development of breast cancer.

Colleen:
Yeah, we had Dr. Angela Lanfranchi on our show talking about that at one point—how hormonal birth control also leads to an increase in breast cancer. Right?

Dr. Joe Malone: A woman who has—this is a shocking statistic to me—a woman who has her first child around the age of 20 has half the chance of developing breast cancer as a woman who has her first child around the age of 30.

So again, the picture I got—and I won’t go further with this now, but there is more on promiscuity in terms of lifetime sexual partners, which I can mention later—but what jumped out at me, Colleen, was that the classic Catholic family…

By the way, Dr. Fagan—I think he has seven kids—the classic Catholic model of saving sex for marriage, and not allowing premarital sex, and then getting married probably earlier because of that in a lot of cases, and then starting to have children earlier, and having many children—being open to the procreative and unitive functions of the sacrament of marriage. And then breastfeeding—all of that has a tendency to make women’s downstream health effects the optimal, the most positive they can be.

And with breast cancer becoming the number one cancer diagnosis in the world as of 2020, you know, that’s an important realization—especially for young women to have. So it was things like that—almost miraculous, really—that mapped on so exactly to what I had already researched and found. Especially in contrast to how we do things now—how young women and young men aren’t getting married until much, much later. Some are never getting married, some never having children, and then you see the effects of that.

I just thought to myself, when I was talking to Pat up there at CUA: “You have the cleanest philosophy I think I’ve ever seen—and the most accurate I’ve ever seen or witnessed.” So that would be my answer to that.

And then the other thing that’s related to it—and I think this is interesting—is that when I discovered that sexual wellness is sexual integrity—and by the way, sexual integrity is sexual intelligence—that’s how it all links up, and we can explain more of that as we go…

History of Pair Bonding in Humans

When I discovered that, I got on the internet because I thought, “Okay, really the whole of humanity sits on this foundation of sexual integrity.” Because if you look at humans scientifically, going back millions of years, what science tells us is that about two million years ago, this whole pair bonding in humans thing started. And pair bonding in humans is what allowed the human brain to triple in size from that time to now.

That only happened because the male and the female worked together—pair bonded and worked together—with the male provisioning the female. Or in today’s language, the husband provisioning the wife.

And during her pregnancy, you know, it takes 500 extra calories a day for a woman to carry a child. And then another 500 extra a day when she’s breastfeeding. It doesn’t sound like much to us, because hundreds or even thousands of calories come easily in our society. But back in a hunting and gathering context, 500 extra calories was a tremendous amount to bring in.

So this partnership that started—again, what the science, the best science, will tell you—and I think the accurate science will tell you—happened because of what they can determine from the size of the skeletons, the bones that they’ve found. As they trace this down through time, they’ll tell you that six to seven million years ago is when the human line started. And it was polygynous to begin with—polygyny meaning, from the Greek, poly meaning many, and gynē meaning female. So, one man with several wives.

For about four or five million years, we had a polygynous situation. In any kind of polygynous species, you’re going to see that the male is much larger than the female. And the bone fragments, the skeletons they’ve found, show that males during that time period were about 50% bigger than the females. That’s quite a contrast—today, we’re only about 15 to 20% larger. That change is associated with becoming more monogamous as a species.

In monogamous species, for a lot of different reasons, the body sizes of the male and female are either exactly the same or very close. What that tells us, among many other things, is that over time—especially in the last two million years or so, when fire was discovered and humans started doing more sophisticated things like running animals off cliffs, and taking advantage of our increasing brain size—it really made human exceptionalism what it is today. That same evolutionary path put us on the moon, and now you and I are having this conversation over who knows how many miles.

Now, compare that to chimpanzees and where they are. Chimpanzee fathers, once they impregnate the female—and by the way, they have a very promiscuous mating system—once a female chimp goes into heat, her genitals swell in a way that’s visually and even olfactorily stimulating to the males. Most of the males in the troop (or pride—whatever the proper term is) will mate with her.

So their mating system involves what’s called sperm competition. You can see this physiologically. For example—probably more than you bargained for in this answer—but you can observe this in species: males in promiscuous species tend to have much larger testicles than those in monogamous ones. Chimpanzees, even though they’re smaller than we are in body size, have testicles three times the size of ours. That’s because, over time, those with more semen had a better chance of fathering offspring when multiple males mated with the same female.

Now, that hasn’t been a factor for us humans in the last two million years because we’ve mostly been mating monogamously.

Another difference—besides testicle size and the female’s sexual swelling—is this: chimpanzees don’t get bacterial STDs. They’re effectively immune. Why? Because they’ve been promiscuous for thousands of generations. The individuals that did get bacterial STDs didn’t survive to reproduce. So, over time, they developed higher white blood cell counts than we have—significantly higher.

Anyway, all that said, I believe—personally—that God had a design in all of this. That’s my belief: that it was intelligent design all the way through.

And the way He created humanity, the key thing was this—what we now call the sacrament of marriage. That allowed surplus energy to be directed into the women: into pregnancy, into carrying the baby, into nursing the infant. Then soon after, having a toddler, becoming pregnant again, and continuing that cycle. You know, having a toddler, then having another pregnancy, and on down the line.

So I thought to myself, this is—like—this is profound. And I can’t be the only one who has realized this. So I said, I’m going to search the internet, and I know—I know—there will be hundreds, maybe thousands, of people working on sexual integrity, because it’s such a key part of our history.

Nope. There were two. Just two entities working on it. One was this group trying to help teenagers stay off porn, and the other was Heartbeat International.

So, I contacted them via email, and they got back to me. They said, “Let’s get on a phone call.” So we did. Right away, they asked, “Who told you about us? Who told you to call us?” And I said, “Nobody.” I described the circumstances—what I’d done—and they said, “This has got to be a God thing.”

They said they’d had a sexual integrity program they started about 20 years ago, but it had been dormant for the last seven years. And they were just getting ready to launch a new version of it. They said, “We want somebody new to lead it. Would you be interested?”

Would I be interested? Very. So I’ve been working with them, speaking at their conferences for the last—I think—two or three years now.

Anyway, I say all that to say this: sexual integrity, if I haven’t defined it for you already, is the idea of saving sex for marriage. And in a minute here, when I describe this, you’ll see why it’s so important. It means marrying—one man marrying one woman—and creating a family in which the children enjoy the benefits of having both a father and a mother. All the good that comes from that. The opposite of integrity would be, kind of, a lot of the things we’re doing today.

Colleen: What is the most fascinating thing that you’ve learned studying all this? Like, what stood out to you the most or surprised you?

Dr. Joe Malone: There are so many things that have been fascinating. One of them is the fact that you can tell what kind of mating system a species has—whether it’s monogamous, polygynous, or even polyandrous (which would be one woman and many males, though that’s extremely rare). That’s been one thing.

But probably the most important—and the thing that stood out to me the most—is what I’m about to tell you now: how men bond differently than women do. And how it fits in with the Catholic teaching on sexuality.

How Men and Women Fall in Love and Bond—Chemically!

Colleen: Let’s just dive right into that then—can you explain how men and women fall in love and finally bond? Because you posed this as a potential topic, and I looked at it and thought, yes, let’s do this. I’m really excited to hear about this, because I think it’s so interesting—the biological and physical components of how men and women fall in love.

We’re body-soul composites, so it’s going to be a huge part of it. And I think that sometimes people either put too much emphasis on it, or just neglect it entirely, depending on which circles you’re in. But recognizing that there’s a very physical part of falling in love with someone—yes, it’s so important. Especially these days, where there’s so much confusion and, I think, despair. Especially on the part of women, because I think it’s more instinctive for women than men—to bond and to fall in love.

Dr. Joe Malone: Let me just take you through it. And if you have a lot of female listeners, this is really headline news.

When I’ve spoken about this on college campuses, the young women in the audience—it was really strange at first. I thought, Why are they taking their phones out? They’d start raising them up and filming. I think they wanted to show this to their boyfriends. It was a strange phenomenon.

So, here’s the deal: men’s bonding response is more complex than women’s. There’s biological sex differences. The main bonding biochemical for males is one called vasopressin. Some people pronounce it differently—vasopressin, vasopressin—but the important thing is this: it has to be in the male brain for a long period of time.

If it stays in the brain long enough, the body will start forming receptors for it—because that’s how these things work. But the thing about vasopressin is that it can be washed out by the chemical explosion that happens at orgasm. That includes serotonin, oxytocin, and—especially—opioids. Opioids are the big one.

So the picture that arises is this: the old-school, chaste dating model—where there’s respect between the male and female, where he’s around her a lot, loving every minute of it… going to dinner, going to movies, hugging, kissing, light physical contact—all of that raises endorphin levels, which is another bonding chemical. But they’re avoiding outright sex, especially sex to orgasm.

That is what, over time, binds him to her. Because what’s happening is this vasopressin molecule is gradually building up in the brain, and eventually, the receptors form. The question I always get on college campuses is: “Dr. Malone, how long does it take?”

And I only grudgingly tell them—but I want to be honest—so yes, I tell them. Eventually, the vasopressin molecule docks. And when it does, something significant happens: his testosterone starts dropping.

Now, his testosterone had been high because he was around this woman he’s sexually attracted to, all the time, and he’s not—quote-unquote—”getting anything.” But once the bonding—once that docking—takes place, his testosterone comes down.

Then, the secondary bonding chemical for males—oxytocin—which is actually the primary bonding chemical for women, comes into play. And now there’s a double bond. That’s when he becomes, in a good way, territorial about her. She’s his woman. That kind of thing.

Again, going back into the past—back when we didn’t have an expectation of sex before marriage—let’s say 1960 and earlier, that process played itself out over and over again. And it really worked to the advantage of both men and women.

Because if a woman is being promiscuous with a man—if she’s “easy,” so to speak—that whole vasopressin bonding process goes out the window for a couple of reasons. One, biochemically, it just doesn’t mix. And two—and this is really important for women to know—men, especially high-testosterone, alpha-male types, tend to start categorizing women right away.

If she’s easy, he’s going to put her in the “for a good time only, but not for marriage” category. If she’s not, he’ll categorize her into the “marriage potential” category. Now, this isn’t based so much on chauvinism, like a lot of women might think. It’s really rooted in an insecurity in men. A couple of things are at play here in their biological sex differences.

Women have what we call female choice—that’s based on finding somebody with genes that really appeal to her. In other words, the good-looking guy, the hunky guy, the one who would produce great children. But then there’s the other consideration: the kind of man with enough character to stick around, be honest, and be a good partner.

So she’s balancing female choice with his paternity certainty. Because with internal gestation, only the woman knows for sure who the father is. Over time, it’s been very important for men to be able to trust that the child is theirs.

It turns out that sexual integrity and sexual loyalty are the most highly valued traits in a woman a man is considering marrying. Women need to know that. Another thing women often don’t know is this: after unmarried intercourse, a man’s evaluation of a woman often starts to drop—typically about ten seconds after he orgasms. It doesn’t take very long.

Colleen: Because the bonding chemicals are washing out?

Dr. Joe Malone: Exactly. The bonding chemicals are gone, and he’s on to the next. If he’s got his phone nearby—maybe I’m being a little facetious here—but soon he’s going to be looking at Tinder or whatever else, looking for the next one, and the next one.

Hookup sex gives men a huge dopamine rush. And, of course, testosterone stays high. That combination keeps him going and going, but he never gets to that pair bonding in humans stage—the vasopressin and oxytocin stage.

What women don’t realize is that they bond a lot more easily than men do, due to biological sex differences. I’ve worked with two young women who each had a parent—one a mom, one a dad—who destroyed their marriages by cheating. These parents, now single, told their daughters, “You’ve got to have sex with a guy in order for him to consider marrying you. You’ve got to let him test you out.”

But that’s the worst thing they can do. Here’s the scenario: she has a more simple bonding process. All it takes is dopamine—from being around him—and oxytocin, which rises from hugging, kissing, being close. And especially if they have sex, her oxytocin spikes.

She’s bonded. Because of biological sex differences, she’s thinking, “He’s better looking than I thought,” or, “He’s such a great guy—he’ll make a great husband and father.” But what she doesn’t know is that giving it up too soon has destroyed that chance.

This is why, back in 1960 and earlier, only about 5% of births were out of wedlock. Today, we’re at 40% overall, and some ethnic groups are up to 70%. We’re in a horrible place as a society because we’ve departed from these norms. Let me give you something, Colleen—and for your audience—that I think is really important. I want to sum it up in two ways.

One: The research shows that the shorter the time to sex in a relationship, the shorter the relationship.

I’ll say it again: the shorter the time to sex, the shorter the relationship. So first-date sex—boom—the relationship usually lasts next to nothing. On the other hand, the longer a couple waits to have sex—on a population basis—the longer the relationship tends to last. Now, I think your and my bias is to wait until after marriage, however long that is. But the research supports that it leads to better outcomes.

I was talking to a young woman at Florida State University, and she asked me, “What’s the number one thing that causes marriages to break up or be unhappy?”

I looked at her and said, “The number of premarital sexual partners has the biggest effect on whether a marriage will last and whether it will be happy.”

She didn’t like that answer. She kept trying to find a way around it—“It can’t be because of that.”

But I told her—and I’ll tell your audience—these are population averages. There are always exceptions. But for the most part, your best indicator of how a marriage will go is: How chaste have you both been up to that point?

So again:

• The shorter the time to sex, the shorter the relationship.
• The more premarital sexual partners, the lower the chance of marital happiness and longevity.

And the other thing that young women need to realize is that at every stage of commitment, male testosterone drops. Again, it’s biological sex differences.

So what I mean by that is: he gets a girlfriend—his testosterone drops. They become engaged—it drops again. He gets married—it drops some more. They start having children, and when he holds the children—they’ve found out that the dad, the new dad, who needs to hold the child because there’s a pheromonal exchange that goes on—his testosterone drops the most of all.

Colleen: Does that differ if the child is a boy or a girl? Does that affect it? Because I’ve heard that it does, but I don’t know. I’ve never seen the science on that.

Dr. Joe Malone: I have not seen any research that shows a different sex affects it. But the research I have seen shows that testosterone drops by 50% at that point. And his cortisol drops by 300%.

So here he is—this relaxed, low-testosterone guy. And at the same time, the woman’s estradiol—which is one of the three types of estrogen—rises by 200%. Estradiol and oxytocin are buddies; they boost each other. So that bonding process with the child really gets strengthened by that course of events, through that biochemistry. It’s another example of biological sex differences.

Again, when I look at this, I see God. I see that God has instituted this pathway—this life course—this biochemical life course. And when we go away from it, we pay for it in certain ways.

Here’s the thing: chronic high testosterone is bad for you. That’s one reason that, generally, men don’t live as long as women. It’s unhealthy. While chronic high oxytocin—which we get from marriage relationships, family relationships, hugging, bonding—is very healthy. It’s actually cardio-protective for one thing, and it lowers cancer risk.

Testosterone raises the problems; oxytocin lowers them. Marriage is the pathway to this. That’s what I want young people to see—we’re sacrificing a lot of our well-being when we go away from that.

Colleen: Now my question—okay, I have three. And they’re kind of all, really, ones that have come up as you’ve been talking, and I’m curious about them.

First of all: How long is the pair bonding in humans process? Because you said women ask, and you don’t like to tell them, but then you tell them anyway—so I’m curious.

Second, how does porn affect pair bonding in humans? Does it cause chemical disruptions that keep men from bonding?

And third, if premarital sex is going to make a man start looking for another woman, how does sex after marriage affect pair bonding in humans?

Dr. Joe Malone: All right. So, the answer to the first one—the dreaded answer I have to give—is: four months. It has to be at least four months of dating, chastely, before that the pair bonding in humans process can really take place.

Now again, I would advocate a year, year and a half, maybe even two years of chaste dating—and then getting married. That way, you really know each other well. Now remind me of your second question?

Colleen: How does porn affect pair bonding in humans—for both men and women?

Dr. Joe Malone: Porn is the elephant in a lot of rooms these days. It’s like an artificial sexual partner, really—especially for men. Males have six times the likelihood of being addicted to porn than females do.

Unfortunately, I think today it’s taking the place of real human relationships for a lot of boys and young men. The average age of first exposure is between 10 and 13 years old. They’re getting addicted—bonded to it—at such a young age. And it puts them into depression.

As I said earlier, in hookup culture, when humans—especially males—are having sex frequently, they’re coming to orgasm. Let’s just put it that way. I hope I’m not being too graphic for your audience or for you, but it’s hard to talk about this subject truthfully without using direct language.

When they’re orgasming often—say, every other day—especially through porn, and especially having started at such a young age when their minds are still plastic (pre-teen or early teen years), that becomes their sexual map. That becomes what their brain is wired to respond to.

Now, let me give you an analogy from research with rats, whose brains function in very similar ways to ours in terms of reward, bonding, and arousal—even though they’re obviously much smaller.

What scientists have done is take a young male rat just coming into sexual maturity, and place him in a cage with an estrous (in-heat) female rat. Normally, the male rat will find a way to mate with her. That’s typical.

But in another condition, they did something different. They placed a hammer—or some inanimate object—into the cage during his first sexual experiences. At the same time, they manipulated the brain chemically—with dopamine, testosterone, etc.—to create arousal while he was near that object.

The result? That young male rat became sexually imprinted on the object. When they later introduced a real, in-heat female rat, he wasn’t aroused by her. He had already bonded to the object. That’s similar to what I believe is happening with young boys who get hooked on porn.

While I haven’t seen as much hard data specifically on porn and pair bonding in humans—that’s a very good and unique question, by the way—my strong professional suspicion is that these young men have already bonded to that activity. They’re addicted to it, and it disrupts their ability to form healthy emotional and physical bonds with real women.

And they don’t have to go anywhere. They don’t have to take risks, like asking a girl out. They don’t have to experience rejection. Their sexuality is in their bedroom, or wherever they watch it. So it’s very destructive. Very destructive—especially on the male side.

Now, on the female side: generally, women have not been as vulnerable to porn addiction. But that’s changing. And here’s something your female listeners should be aware of: the research has shown that the earlier a female experiences sexual arousal, the more open she tends to be to things like casual sex, porn use, and related behaviors.

That’s what researchers call sociosexuality. I don’t love that term, because it makes it sound neutral or academic, but it basically measures someone’s willingness to engage in casual sex, porn, hookups, and so on. So, for example, girls who are exposed to porn early may become more open to those behaviors and experience some of the same problems.

Also, girls who are sexually abused—which, obviously, is not their fault—but who experience sexual arousal very young, often end up with a very different trajectory. They can become, in a sense, a different “breed of cat,” so to speak, compared to a typical young woman who hasn’t been exposed to it. There’s a huge sex difference in terms of drive, bonding, and willingness to engage in casual sex.

And the third part of the question was… remind me?

Colleen: If sex before marriage makes the man start looking for another woman—what happens to the pair bonding in humans with sex within marriage? Does it actually draw him closer to the woman, or is there still a change in their bonding because of that?

You said that with premarital sex, a man doesn’t bond with a woman. He starts looking for the next woman. How is that different within marriage? What chemically is going on with him if he’s actually married? If a man practices chastity and saves himself for marriage, and the woman also practices chastity and saves herself for marriage, how does sex affect his pair bonding in humans with her within marriage?

Dr. Joe Malone: Oh, it’s perfect, actually. Except for one thing. You know, with the whole purity culture of 15 or 20 years ago, or whatever it was, they made sex so—like, I don’t know—stigmatized, I guess. So much that they weren’t even supposed to think about attraction.

There’s one guy who wrote the book I Kissed Dating Goodbye. I think, when they went too far with that—making sex seem bad and avoiding any kind of physical affection like hugging or kissing—the effect on some people was that they got to their wedding night and were both virgins, and they were both intimidated by it. I have people I know who’ve shared that story with me.

So, I think if you handle it correctly—like, again, in the old days, where it was just expected that you were going to remain virgins until marriage, and that was the norm—I think it works fine. Again, it’s so rare these days that it’s hard to even do research on it. Same with porn—because they don’t have anyone for a control group who isn’t watching it.

The first research they did in 2009, they couldn’t find anybody on a college campus that wasn’t using porn. And there are so few now who are remaining virgins until marriage. But that’s the best-case scenario—as long as it hasn’t been stigmatized.

The pair bonding in humans will take place very, very well. Both people have worked on their “muscles,” so to speak—their chastity muscles—by resisting temptation along the way. And so it’s, I think, the way it was meant to be.

I have a friend—a colleague, actually, a female colleague in Texas—who was a virgin until age 32 when she got married. I met her before she got married. She was Miss Texas and was on a reality dating show. Her husband was a Major League Baseball player, and he was a virgin as well—around the same age. They had both saved themselves for that long. Once they got married—they’ve been married about maybe two years now—it’s been great. They’re kind of an example of what I’d call a unicorn these days.

Colleen: So specifically, sex within marriage is going to make the man bond better with the woman?

Dr. Joe Malone: Yeah, because he doesn’t have to worry about her having had experience with somebody else and comparing him to someone else.

Again, instinctively, men find women who are easy suspicious—especially in terms of long-term commitment. It’s kind of like, in the wild, when an animal finds its prey too easily. It usually doesn’t happen that way. Generally, you have to work for the things that are worthwhile.

So, I’d say it’s the best-case scenario as long as it isn’t stigmatized to the point where they’re afraid of it and can’t do what comes naturally after they’ve fully committed to each other in marriage.

Colleen: I have a question too that you might know the answer to. People talk about “the chemistry” between men and women. Is that a personality thing, or are there people who are more attracted to each other based on a chemical makeup? What role do chemicals and hormones play in the chemistry and how men and women fall in love?

Dr. Joe Malone: Another excellent question—and yeah, pheromones. Have you heard of pheromones?

Colleen: I mean, you mentioned them earlier with the father holding his child, but I haven’t heard much about them.

Biological Sex Differences Between Men and Women

Dr. Joe Malone: Well, it’s really obvious and well-accepted in the so-called “animal world”—you know, other species, even all the way down to insects. That’s how they do a lot of their communication, especially sexual communication.

And more recently, humans have been shown to have pheromonal communication, too. It’s not actually a smell, necessarily—we don’t sense it as a smell—but the organ that picks up on it is up in our nasal cavity. And what it does is, this pheromone that one sex gives off affects the behavior of the other sex.

To your question: yes, there are certain people who are not going to be attracted to each other on this chemical basis. One example is family members. That’s one reason why a brother and sister—who could be objectively attractive people—are not attracted to each other. It’s because they share an extremely close match in what’s called the Major Histocompatibility Complex, or MHC.

The MHC is essentially our immune system. God designed us, literally, to be attracted—on a chemical level—to people who are different from us in terms of MHC. The wisdom and beauty of that is that when two people who are genetically different in this way come together and have children, those kids are going to have a stronger, more robust immune system than either parent.

So that’s one of the examples of intelligent design—how God designed us to be drawn to each other based on complementarity, not similarity, at the genetic level.

Now, in terms of biological sex differences, women have a specific type of pheromone called copulins—named after “copulate.” These are present in a woman’s vaginal secretions, and during her natural monthly cycle—not when she’s on hormonal birth control—these copulins become more active.

As she approaches what’s called her ovulatory window—which, if you’re counting from the first day of her period, is typically around day 8 through day 14 on a 28-day cycle—these copulins move from deep inside (near the cervix and uterus) to closer to the vaginal opening. At this point, men who are in close proximity can pick up on them, and it stimulates male sexual desire.

There was actually an interesting study done in Las Vegas with lap dancers. The dancers who were not on hormonal birth control—and who were in their ovulatory window—made 75% more in tips than when they were not in that fertile part of their cycle compared to women who were on hormonal birth control.

Colleen: That’s another question then. It’s related to this. Due to biological sex differences, are women more attracted to men when they’re in that part of their cycle?

Dr. Joe Malone: Yes. Yes, as a matter of fact. There’s so much important and interesting stuff to learn here. I really became a better self-manager once I learned all this. And that’s my goal with whoever I get to share it with.

So yes, a woman’s sex drive is highest during that ovulatory window. Particularly if it’s combined—though it doesn’t have to be—with alcohol. Alcohol raises women’s testosterone levels. It raises men’s slightly too, but if men drink too much, their testosterone actually drops—more biological sex differences.

Women, though, naturally have so little testosterone compared to men—men have about 20 times more on average—that they’re not used to its effects. And of course, alcohol also inhibits the frontal cortex, so it lowers inhibitions. So if a woman combines alcohol with that fertile time in her cycle, she’s much more driven sexually—and often much more reckless. It’s a time when bad stuff can happen, or things can happen that she wouldn’t normally go along with.

The research even shows that women tend to dress more provocatively during that time—especially single women. And if a woman who’s married is going to have an affair, it’s most likely going to happen during that fertile window—and typically with someone who is genetically superior to her husband. You know, “the hotter guy,” so to speak.

So yeah—it’s a dangerous time, especially in terms of casual sex and especially with alcohol involved. Honestly, alcohol is probably the closest thing to an aphrodisiac for women that I can think of.

Now, back to pheromones. Copulins are really interesting, but there’s another pheromone group called androgens. “Andro” comes from the Greek word for male. Due to biological sex differences, these are the pheromones men give off. And females—this is a bigger deal for females—they’re better at detecting them than men are.

By the way, the female sense of smell is much more acute than a male’s, on average. So here’s what’s fascinating: in a committed relationship, like a marriage or an engagement, researchers have done studies where thousands of men wore t-shirts for a week—no cologne, no deodorant, nothing artificial. Then they gave these shirts to women.

What they found was that women who were bonded to their partners could pick their man’s shirt out of all the others—based solely on scent. And it’s not even that they were smelling it, per se—they were just sensing it.

Another amazing thing: women can detect genetic symmetry in men through scent. They’ve done similar t-shirt studies where some of the men had more asymmetrical features—things considered less attractive—and others were more symmetrical and masculine. The women consistently chose the shirts of the more symmetrical, more genetically “fit” men.

So I guess the point we’re making here is that a lot of attraction between people really is chemistry. Not just emotional chemistry, but literal, biological chemistry. And it’s happening at an unconscious level—in the limbic system, which is the emotional center of the brain. And it’s due to biological sex differences.

If we were to talk about one more of the major biological sex differences, it’s that the limbic system is also where the sex drive is located—for both males and females—but it’s much more dominant in the male brain. People are drawn to others even without the visual component, although visuals are still important.

One other thing about biological sex differences: kissing plays a big role in pheromone communication—especially for women. Think about it: during a kiss, pheromones are present in the saliva. So when a man and woman kiss, they’re exchanging chemical information.

Research shows that almost no men will break off a relationship—or pass up a chance for sex—because of a bad first kiss. But 50% of women will. If it’s a bad kiss—if the chemistry isn’t there—half of women will lose interest entirely. That’s how sensitive they are to what’s happening at the chemical level.

Women have more to lose from a bad match. Because their body creates the baby. The man contributes the DNA, but the woman’s body is the one carrying the child. So the stakes are much higher biologically.

Colleen: I’ve read that when men and women kiss, there’s a hormone in the man’s saliva that turns the woman on, and that there’s a hormone in the woman’s saliva that makes the man bond to her—like, it actually triggers bonding, not just the sexual high. Is that true? And is there any other weird stuff going on when they kiss due to biological sex differences?

Dr. Joe Malone: That particular piece of research I haven’t heard before, but it does make sense, based on everything else I know. Women have a tendency to carry these natural reinforcers for pair bonding in humans—kind of like internal “pair bonding in humans encouragers” built into their biology. So that would make sense.

For the guy’s biological sex differences, maybe not as much—but again, it’s very possible. I just can’t say I’ve seen specific research showing that exact hormone exchange via kissing.

There is a related element I can speak to, though. For example, when women have sex with a man—especially in cases where it’s non-consensual or becomes non-consensual during the act—there’s evidence suggesting the female body can become somewhat inhospitable to the semen. Not in our species specifically, but in some animal species, they’ve observed what’s called cryptic female choice, or cryptic rejection, where the female’s biology actively works to reduce the likelihood of conception if conditions aren’t right.

So, there’s a lot of chemical communication going on—sometimes even chemical warfare, in a sense. There’s what researchers call sexual conflict—and other times, there are biological mechanisms promoting pair bonding in humans, especially on the female side.

On the male side of biological sex differences, I’ll add this about semen: when a man ejaculates inside a woman, she doesn’t realize it, but his semen contains compounds that actually make her feel better. Off the top of my head, some of the chemicals in semen include: Serotonin, Endorphins, Oxytocin (in some studies), FSH (Follicle-Stimulating Hormone), and LH (Luteinizing Hormone).

FSH and LH are hormones her own system also uses to stimulate ovulation. So he’s literally contributing to her hormonal and emotional environment. His semen is absorbed in the vaginal wall and affects her body—physiologically and emotionally.

That fact alone, honestly, screams monogamy and chastity. I tell every group I speak to: within a committed relationship, when a man and woman are having what we’d call unprotected sex—without a condom—it’s actually very beneficial to both of them. Especially the woman.

In fact, research has found that women in strong, committed marriages who have unprotected sex score significantly lower for depression than women who are not married—or who are sexually active, but the man uses a condom. Those women aren’t receiving those chemical benefits, because the semen isn’t entering the system and being absorbed.

There’s element after element that supports this idea of biological complementarity—and if we had more time, we could go even deeper into all of it.

Why Chastity is Better—Biologically—Than Casual Sex

Going on with biological sex differences—again, a huge one. The front-page news is that men don’t bond through casual sex. And by the way, “casual sex” is an oxymoron, because there’s nothing casual about sex.

So, women that are listening, know that you’ve got a superpower. The superpower is called chastity—chastity until marriage. And the guy—if the bar is low, as far as obtaining sex, the guy will slither over it. Thankfully, if it’s high, he will find a way to get over it. And high is where you want to be—the conditions you set—which is historically what’s happened.

Even in other species, the females demand certain things to happen before sex occurs. Alright, why is this so important? What drives males to go through all that to get sex? Well, because of biological sex differences, men are much more easily sexually stimulated than women are. There are three areas of the male brain that are twice as big—and they’re the sexual pursuit areas.

One’s called the medial preoptic area, and as the name implies, it’s located right behind where the optic chiasm comes into the brain, right there in the hypothalamus. And it’s—like I said—twice as big and packed with twice as many neurons. So, very sensitive to sight. That’s why women may find themselves with a guy on a date, and he’s kind of scoping the room. Well, it isn’t so much you, lady, that is the problem—he’s kind of got this built-in thing going on there. Also, that area is very sensitive to testosterone levels, and men, on average, have 20 times more testosterone.

Another area of the hypothalamus, which is really the seat of sexuality in the human brain, is called the INAH3. I’m not going to take time to go into that, but it’s another sexually important area that’s twice as big—again, packed with twice as many neurons—and also sensitive to testosterone stimulation.

The third area I want to mention is the amygdala. The amygdala is also twice as big in males and packed with twice as many neurons. It’s sensitive to sexual cues in males—intensely—and to testosterone. The amygdala is the brain’s survival command and control center, and so when it makes a statement, when it gives a signal, it’s pretty hard for the male brain, in this case, to ignore it.

Interestingly, women’s amygdalas are very sensitive to food cues. And again, that may go back to the way it was for our ancestors.

One thing—it’s not even just the huge difference in the 20 times more testosterone that men have—women also have 13 times more sex hormone-binding globulin (SHBG). So now we’re really getting into the chemistry here. SHBG deactivates testosterone and estrogen. So you really have a major mismatch in the male brain versus the female brain when it comes to sex drive in most cases. There are a few exceptions, but it’s really, really massively unequal.

Colleen: How does that affect their interactions? Like, what… I guess you’re about to answer it—but what is the reason for that? Because that doesn’t seem like a good thing.

Dr. Joe Malone: Well again, in the past—and this goes back over two million years—men have not always had a choice on sex except for meeting what the female demand was for it. So it’s been a strong drive for them. They reach their highest level of testosterone at age 17, and it stays high throughout their 20s. It only starts going down about 5% a year after age 30.

To me, Colleen, again, in God’s design, that is to drive young men toward being willing to commit to this young woman who’s demanding a certain romantic and chivalrous behavior from him. And he’s going to commit to her at some point.

You compare that to our hookup culture—you don’t have that. You don’t have the women laying down the law, which has historically been their role. And I believe, given to them by God, as part of their sexual nature.

So, the purpose of chastity, the Catholic teaching on sexuality, and the traditional expectations would be to drive men, who wouldn’t necessarily want to commit given other choices, to commit. Basically, to play by the rules in order to be around this woman. You know, the chastity rules that we talked about, for that vasopressin process—and then the oxytocin pair bonding in humans process—to be able to take place. That’s what I think the purpose of it is.

It’s gotten haywire, though, with the idea that men and women should act just the same. The phrase they use is that women should “F like men,” you know? And if you don’t, you’re being repressed and all of that. So that’s really been a bad, ungodly pathway—contrary to the Catholic teaching on sexuality. And that’s one of the main things that needs to be fixed in order to get us back to where we need to be.

Colleen: I do. So, if women are supposed to set this high bar of chastity, and men need to have that high bar in order to commit to women, what does that mean for women who have a high bar in a society where other women are willing to sleep around?

Like, will men actually rise to that occasion, or are those men just going to settle for the women that are easy to get? I know you were saying they don’t like it when it’s easy, but it seems like you have an imbalance—if some women are setting the bar really high through chastity and some women are willing to sleep around—and men need to have a high bar to commit, what does that look like in today’s modern age where you have such different situations going on?

Dr. Joe Malone: Excellent question. It’s a tough situation for women—especially women practicing chastity. Really strongly believing Christian, especially Catholic women, following the Catholic teaching on sexuality, it’s really tough.

But what it comes down to is this: the women that the men are sleeping around with can pretty much count on not getting someone to commit to them as life goes along. The woman who won’t play the game, and is doing things the way I believe God intended them to be done, may have to wait a while because of this situation. But eventually, I think she’s going to be the one.

She has the scarce resource. She’s the rare one who hasn’t been with a bunch of other guys. The guy doesn’t have to worry about that. She’s kind of “proof of concept” that she can be loyal, and that her sexual integrity is important to her. She’s not just going to give it to any guy. So, it’s a quality-versus-quantity concept.

The quantity—the guy will take as far as every day, for a week or two or whatever—and then he’s on to somebody else. The woman practicing chastity is the one who’s going to get his attention, as far as a marriage partner. That type of thing. That’s literally what the research has shown.

Now, things like how attractive she is, you know, that enters into it—those are the tough types of variables. But another thing to throw in here is that around 80% of men, given the chance to have easy, quote-unquote, casual sex—something they don’t have to pay a price for—will take it.

But the top 20%—this is interesting—the top 20% in intelligence, just general intelligence (IQ), are smart enough to want to have exclusive relationships. They don’t necessarily want to have the hookup situation going on.

So, a woman who’s saving herself in the way you’re describing, living out chastity and following Catholic teaching on sexuality, would be a very attractive partner to one of those males in the top 20% of IQ—someone who’s looking for a partner that shares the same attitudes toward the importance of exclusivity that he does.

So yeah, that would be the answer I would give. When society is the way it is, it makes it really, really tough on women practicing chastity—particularly as society is now.

A Cultural Swing Towards Chastity

The other thing I want to say is that, as a society, we have a tendency to think that history is linear—that it just started out over here being really, really pure back in the old days and has continuously gotten worse and worse, with more and more sexual anarchy as opposed to sexual integrity (chastity). But actually, it’s been ups and downs; it’s been cyclical.

In the last 350 years, we’ve had really three pendulum swings between sexual anarchy—which I would call promiscuity for another word—and sexual integrity (chastity), which is what my life has become all about. So, it’s changed three times in about 300 years, so roughly a little over a 100-year cycle. I think we’re at the tail end of a very bad sexual anarchy phase cycle.

The hardening news is that I think we’re on the backlash of this one, and I think a lot of women are kind of getting tired of it. I think they’re realizing that if, as a union so to speak, more and more of them start not playing the hookup game, they’re going to start raising their value and get more of what you described earlier. You were very astute to pick up on that.

One piece of evidence is that, I don’t know if you or your listeners have heard of the dating site OkCupid. They started around 2004 or 2005 and were smart enough to survey their customers every year about their attitudes toward casual sex and hooking up. From 2004 to 2016, the desire and openness to casual sex and hooking up were always increasing. But starting around 2016, that openness began to decline, especially among females, who have led the way by about 10% a year basically.

So anyway, I think we have empirical proof that what we’ve gone through is a terrible period—probably the worst sexual anarchy period humans have ever been in, probably somewhere up there with Sodom and Gomorrah. But I think we’re due for a swing back in the other direction—towards chastity.

I think what you’re doing, what I’m doing, and what quite a few other people are doing is calling attention to the situation, bringing science to bear on it, and getting the word out there about chastity and how the Catholic teaching on sexuality is the best. I’ll stop there.

Colleen: I would say science and truth always complement each other. The Catholic teaching on sexuality, which has been taught for 2,000 years, is backed up by science, and you see that in so many areas of life. So, I’m really glad you’re able to bring the science to prove that point here.

Dr. Joe Malone: Thank you. I have the same reaction to it, and I think it can be so useful to 20-somethings and 30-somethings, especially females. As we’re going to find out when we go into some more of this, females are much more vulnerable to the problems of STIs and a little heartbreak right off the bat. They’re set up for heartbreak, as we talked about.

In the long run, it being the system that it is—a terrible heartbreaker on women—it really is, but in the long run, it’s really bad for males too. They end up not having the lives they should have, where that sexual energy is channeled into productive means, and where they become great providers, great husbands, great fathers.

It’s destructive to both sexes, profoundly. So, again, the purpose of us having these discussions is hopefully that the folks listening will get wiser by it and not have to experience it themselves. You know, don’t learn by your own mistakes—learn by somebody else’s experience.

Colleen: Thank you so much for joining us today. I look forward to having you back on to talk about how contraception affects pair bonding in humans and everything else there is to talk about.

Dr. Joe Malone: It’s an honor for me. Thank you, Colleen. I’ll look forward to the next time.

(This transcript was automatically generated. Please refer to the original audio to confirm information)