First off, it’s not. All of the research that we have show that it’s only a minority of guys who have multiple partners per year, and I typically talk about this as three partners a year because that’s the Casanova average. It’s actually a minority of guys who want multiple short-term partners — that even comes up in the evolutionary research. The evolutionary argument basically goes that guys have the ability, theoretically, to produce hundreds of children per year, and they can never quite be 100 percent sure that any child is theirs, so they should spread their seed widely. But what gets left out of that is the fact that if you want your genes to go beyond that next generation — beyond your children to your grandchildren, then your odds are better if you actually stick around and help raise that kid until that kid is old enough to pass on his or her genes.

Why has this narrative about seed-spreading become so dominant?

It made it out of scientific circles and into popular culture in the 1980s as sociobiology, and parts of it got recreated as evolutionary psychology in the 1990s. So it’s gotten a lot of press attention as a new theory. Another part is it really caught on because it gives us essentially a simple answer to a difficult question and, for whatever reason, we here in the U.S., if not in many other places, really like those simple answers to difficult questions.

In mainstream media we’ve had all of this stuff on TV since the 1970s that really promotes this idea of promiscuous young men. The history, as far as I can tell, really starts with Fonzie on “Happy Days” and “Hawkeye” Pierce on “M*A*S*H.” And it continues with guys like Sam Malone on “Cheers” and Charlie Sheen’s character on “Two and a Half Men” and Barney on “How I Met Your Mother.” For several years now we’ve had so-called good guys who were also promiscuous. If you looked at TV and movies from the ’50s and ’60s, the promiscuous guys were always very clearly the bad example.

Are there any truths to the Casanova myth?

Well, it’s not a myth. There is a percentage of guys that do that. It’s really more an issue of the numbers. If you look at the public health research tracking things like unplanned pregnancies and sexually transmitted infections, that research typically shows about 15 percent of guys have three or more partners in any given 12-month span. If you follow those guys over time the number of guys who have three or more partners a year for as long as three years, that drops to about 5 percent. So there are definitely some guys out there who are doing it — but it’s really a small percentage of guys. By contrast, if you look at guys who are very religious, that’s about 15 percent of guys, and most of them really are devoutly religious, really dedicated to their partner. There’s way more of that than guys that are having three partners per year for three years.

How do gay men fit into this?

We have a lot less data, oddly enough, about the relationship patterns of gay men. I say “oddly” because you would think that sexual orientation is about whom you’re choosing to date and have sex with and that we’d study their romantic relationships a lot, but we haven’t. As far as I can tell, they follow the same kinds of patterns. There are those gay young men who are trying to sleep with everyone they can, but it’s a minority of guys.

We constantly hear that young people these days are hooking up instead of dating, is that true?

Yes and no. Let me go back to the religious guys for a minute. They will often talk about dating as courting and using this model that comes to us from the 1950s: you met someone you were interested in, you asked them out on a first date and then a second date, and there was this fairly clear understanding of what type of physical behavior was supposed to happen. There’s this book from 15 years ago, “The Rules,” that really spells that out. For the religious young men, they still follow that script.

But what most young men and young women are experiencing today is that we’ve gotten away from that script. That’s in part because it is now very common for teenage boys and adult men to be friends with young women. We don’t have that separation of the sexes that we used to have, and we have a lot more time where folks are hanging out. You don’t really need to date someone to get to know them the way you did 30 or 40 years ago. So what we’re finding out is a lot of the ground that used to be covered on the first, second and third date — potentially things like first kiss and maybe even some groping or fondling — that happens in these much less-structured spaces of hanging out. So the beginning of couplehood is much less defined, but what typically happens, say, for undergraduates is after a twosome has been hanging out for a while and kissing and doing whatever else sexually, eventually they will have this conversation about “Are we a couple now?” And then it becomes formal and they are a couple, or perhaps not. But we’ve lost those early markers of first date, second date.

What do we know about what young men are looking for in those committed relationships?

What most guys seek, and this seems to be regardless of sexual orientation or age, they’re looking for people whose company they enjoy. People who appreciate them for who they are. We know that a couple tends to be similar in age. More often than not folks match on ethnicity, political orientation and religiosity. The thing that ultimate grounds it are personality match, similar sense of humor, similar tastes in music, TV and movies, similar activities, because you want to be able to do things with your sweetie and you want someone who gets you. They want someone who’s honest, who’s not going to tell your secrets and who’s loyal. And, of course, those last are typically the reasons people break up — that or you’re emailing the FBI.

What do you make of the popular wisdom that in hookup culture, young men are pressuring young women into casual sex — that they’re setting the terms of these engagements?

I don’t buy it. When we interview adolescents or undergrads, the girls really have the impression that guys are just interested in sex, that they’re not interested in relationships. What we know is that most guys do get into relationships, they enjoy relationships, they do a lot of things in relationships that are not about sex and they’re not doing them just to put up with them in order to get sex. Guys get something out of relationships; they like relationships. If you add in the fact that average age of first marriage is something like 28 for guys, a lot of guys have the sense that this girl they’re starting to date at 17 or 19 or 21 probably isn’t going to be the one — and yet they are choosing to date. They could easily choose to just hook up — or instead of spending that money in a bar you could get a prostitute — but they’re consistently choosing to be in relationships.

How does the Casanova myth impact female sexuality?

One of the ways it impacts girls and women is they get the wrong proportions. They’re told that most guys, if not all guys, just want sex, that they don’t want relationships. So we have a lot of stories and evidence that girls are putting their bodies out there and doing things sexually in order to entice guys into relationships. We’re giving girls the wrong percentages which makes them perhaps behave in ways in which they wouldn’t behave otherwise — starting your contact with somebody sexually instead of relationally, for example. [Some have argued] that because we give girls this image of boys, girls are taught to not attend to their own desires and own sexual wants. So girls’ whole sexuality is really about both enticing desires from boys and also controlling that desire. That introduces some real issues around duplicity and intention. We’re not doing girls any favors here either.

You write that we see high-profile cheating scandals “simply as a guy trying to ‘get some’ on the side.” Is there not something to be said for acknowledging infidelity and recognizing monogamy’s failures?

Absolutely. I’ll talk about General Petraeus, because he’s the scandal of the week. He has chosen to have sex, and let’s highlight the fact that this is his choice. He’s certainly capable of controlling his libido. He chose to have sex with someone he knew very well, this is his biographer, someone who has had access to many parts of his life. This is not him hooking up with some stranger. This is perhaps falling in love with someone else. If we just write it off as, “Oh, it’s just another guy trying to get some on the side,” then we really miss the fact that this extramarital affair really has at its basis a relationship. This is a guy having sex within a relational context. We miss the fact that he’s having a relationship with his mistress — and because we tell the story that way, we don’t get an opportunity to reflect on our own relationships.