When I was in my 20s, watching "Sex and the City," I saw the Samantha Jones character as a sexual role model -- thinking I could have love-'em-and-leave-'em sex like her. However, even when I only wanted sex, I always had a sense of loss when one-nighters didn't evolve into something more. I reflected on this while reading your recent column about how women often wake up after casual sex wanting more from a guy -- even a guy they don't want. But I personally know two women who prefer casual sex. They have it often and don't get attached. Why can they do this?

--Not Teflon

There are those women who, in bringing some himbo home for a hookup, really go that extra mile -- taking a lot of turns on the way so he'll never again find his way back to their apartment.

So, no, "Sex and the City's" Samantha isn't a completely fictional character in how, after sex, she brushes men off herself like large, penis-equipped crumbs. However, in that column you mention, I referenced research from anthropologist John Marshall Townsend, who discovered that Samantha's post-sex detachment is pretty atypical -- that many women who intend to use and lose a guy often find themselves going all clingypants the next morning.

Understanding what allows the Samantha type to escape this takes separating the women who have casual sex from those who feel okay about it afterward.

Women have casual sex for various reasons. For some, it seems the feminist thing to do -- to prove they can do anything a man can do, whether it's working on an oil rig or dragging home strangers for a little nail-and-bail. Townsend notes that women hook up because they aren't ready for a relationship, because they're trying to punch up their sex skills, or -- as with rock groupies -- to get some small piece of a guy they know is out of their league. Other women see hookups as the "free candy!" they can use to lure some unsuspecting man into the relationship van.

There's a widespread belief, even held by some researchers, that higher testosterone levels in women mean a higher libido, but testosterone's role in female desire is like that Facebook relationship status: "It's complicated." Research by clinical psychologist Nora Charles, among others, suggests that "factors other than ... hormones" are behind which women become the Princess Shag-a-lots.

Personality seems to be one of those factors. In looking at what's called "sociosexuality" -- what sort of person has casual sex -- psychologist Jeffrey A. Simpson finds that extraversion (being outgoing, exhibitionistic, and adventure-seeking), aggressiveness, and impulsivity are associated with greater willingness to have an uncommitted tumble.

However, once again, all the reasons a woman's more likely to have casual sex don't stop her from getting tangled up in feelings afterward. The deciding factor seems to be where she falls on what the late British psychiatrist John Bowlby called our "attachment system." According to Bowlby, how you relate in close relationships -- "securely," "anxiously," or "avoidantly" -- appears to stem from how well your mother (or other primary caregiver) sussed out and responded to your needs and freakouts as an infant.

If she was consistently responsive (but not overprotective), you're probably "securely attached," meaning you have a solid emotional base and feel you can count on others to be there for you. This allows you to be both independent and interdependent.

Being "anxiously attached" comes out of having a caregiver who was inconsistently there for you (perhaps because they were worn thin) or who was overprotective. This leads to fear and clinginess in relationships (the human barnacle approach to love).

And finally, being "avoidantly attached" is a response to a cold, rejecting caregiver -- one who just wasn't all that interested in showing up for you. Not surprisingly, perhaps to avoid risking all-out rejection by being too demanding, the avoidantly attached tend to adapt by becoming people who push other people away.

It's avoidantly attached women who social psychologist Phillip Shaver and his colleagues find can have casual sex without emotional intimacy -- and, in fact, tend to see their "discard after using" attitude as a point of pride. (It sounds better to be a "sexual shopaholic" than a person with unresolved psychological problems.)

Other women -- those who didn't have a really chilly caregiver -- are likely to have that "sense of loss" you feel after casual sex. As Townsend notes, female emotions evolved to act as an "alarm system" to push women to go for male "investment" -- that guy who'll go to the ends of the earth for you...and actually come back afterward instead of growing a beard, getting a passport in a fake name, and starting a new life in some remote Japanese fishing village.

I dress like a tomboy: jeans, T-shirts, hoodies, and work boots. My boyfriend of a year wants me to wear skirts and dresses more often. Nothing trashy. Just not my usual tomboy wear. This weekend, I wore a sundress to brunch. It made him so happy, and he kept telling me how beautiful I looked. I did feel a little uncomfortable because I'm not used to dressing like that. Some women in my circle are like, "He should accept you as you are. Don't change for a man." Am I giving up some important source of power?

--Redressed

Your boyfriend's asking you to sometimes wear a dress for him, not hold out your wrist so he can chain you to the pipe in the basement with the six other sister wives.

There are women out there who still see dressing to please a man as some sort of Stockholm syndrome thing -- participating in your own (flouncy, spaghetti-strapped) subjugation. So, it's possible that those advising you "Don't change for a man!" are just trying to help you be a modern and empowered woman. Of course, one could argue that actually being a modern and empowered woman means you don't have to dress like you're hoping to get a call to clean out a sewer line.

Maybe those in your advice coven really do believe they're acting in your best interest. Maybe. Social psychologists Roy Baumeister and Jean Twenge report that it's widely believed that men drive the "cultural suppression of female sexuality" -- which could include shaming women for how they dress. However, in reviewing the research, they make a persuasive case that it's primarily women (often without awareness of their motives) who work to "stifle each other's sexuality."

This is right in keeping with research on female competition. While men fight openly -- "Bring it! I will ruin you!" -- women take a sneakier approach. As female competition researcher Tracy Vaillancourt explains it, women fight for their interests using "indirect aggression," like gossip, mean looks, disparaging remarks, and other underhanded tactics to "reduce the mate value of a rival." Underhanded tactics? You know -- like suggesting you're selling out womankind if you wear a skirt or winged eyeliner.

In other words, your best interest and these other women's may diverge -- though they may not consciously intend to hurt you. As for whether you should throw on a dress from time to time, consider that if you love somebody, you do sweet things for them. Sometimes, this requires a bit of a stretch on your part -- like from the teen boys' section of the department store to that rack in the women's department. A person's clothes say a lot about them, and a man will be happier if his girlfriend's don't scream, "My hobby is crushing beer cans against my forehead."

I'm a 39-year-old woman dating for the first time since the '90s. I'm doing the online thing, and none of these guys look like their photos! It's incredible. When we meet, they always say, "You look just like your pictures." Isn't that the point?

--Frustrated

Guy, in online dating profile: "I'm 55!" Guy's neck, when you meet for coffee: "I was a war hero. In the Peloponnesian War."

Unfortunately, Mr. Peloponnesian Pants On Fire has plenty of company on dating sites. In fact, about a third of the photos people post aren't true to life, according to research by psychologist Jeffrey T. Hancock. Sometimes, that's due to Photoshop; sometimes, the photo is less-than-current; and sometimes, along the lines of "every picture tells a story," the story is "This is how I'd look if I were someone else entirely."

That last kind of lie -- posting photos of somebody else -- is less common than other photographic deceptions, because, as Hancock notes, people have to balance looking good enough to meet with not making somebody stomp angrily away once they do. The same goes for the other lies people tell. Hancock also finds that 81 percent of people on dating sites are lying about their height, weight, and age -- but often just a little.

So, where you go wrong is in your expectations -- expecting online daters to be truthful. As with eBay, a big benefit of dating sites is quantity -- instant access to countless prospects. But there's also a big tradeoff: quality. Going forward, assume everyone on a dating site is lying. Meet prospective partners as soon as possible and as casually as possible. If you're throwing back a $4 latte, as opposed to waiting for the waitress to bring the entree, it's a little easier to make a quick exit from the guy decades older than his picture: "Wow, will you look at the time?! I didn't realize 20 years had passed since we set up our date."

I'm a Harvard-educated man in my late 30s. I've had many ugly arguments with girlfriends, probably because I am highly opinionated and won't give in when I'm right. I've always dated smart, professional women around my age, but I'm now dating a 21-year-old girl, and I'm thinking this could be it. She doesn't complain, bug me, or question or challenge me. It strikes me that having a partner who challenges you is overrated. Could this be a lifelong relationship? Can't I just pursue intellectual discussions elsewhere?

--Peaceful

Why not take this to the next level and get an inflatable girlfriend? You wouldn't need to feed her, and you could save big on travel if you'd just let the air out of her, fold her up, and stuff her in your carry-on.

This actually might make some sense. After all, conflict is bad, right? Well, not exactly. It turns out that there's good conflict and there's bad conflict. Bad conflict involves the stuff of "ugly arguments" -- sneering, mocking, and getting up on moral high ground...just so you can shoulder-check the other person off the edge. Good conflict, on the other hand, involves getting (and giving) healthy pushback -- which means being what Nassim Taleb calls "antifragile."

In "Antifragile: Things That Gain From Disorder," risk researcher Taleb, a former derivatives trader, explains that antifragile is "the exact opposite of fragile" -- but it goes beyond "resilience or robustness." Antifragile describes the way living things are improved by stressors -- becoming better, stronger, and more able to cope with difficult, unpredictable stuff that comes their way.

Beyond how being challenged improves you as a person, marriage researcher John Gottman finds that the happiest, most stable relationships are those in which husbands accept "influence" from wives, making wives "far less likely" to go ugly in disagreements. This starts with what Gottman calls "deep friendship" -- love between two equals with mutual respect, not one person who can't believe his luck at finding another who, intellectually and emotionally, is basically a zygote with boobs.

Of course, this woman's silent partner thing may just be a feature of her being 21. Increasingly, 21 is the new, oh, 8 and a half. Kids are, as Taleb might say, raised "fragile" -- helicopter-parented to encounter as few stressors as possible and then bubble-wrapped off to college for more of the same. Universities, formerly centers of free speech and free inquiry, now have speech codes so nobody gets hurt feelz and have "trigger warnings" about course material, lest someone suffer emotional trauma from something untoward in, say, Plato's "Republic." (Yes, college is now basically nursery school with beer.)

Still, even these kids have to grow up sometime -- which is to say, your girlfriend could begin to have opinions and get a little miffy that you have a heartfelt interest in, um, never, ever hearing them. Your welcoming opinions and influence from a partner -- this woman or a more challenging (but still loving and good-natured) woman -- starts with having humility, which those frail of ego tend to see as a sign of weakness. The truth is, it takes a strong person to admit that he may be wrong and maybe doesn't know everything in the known universe (and any yet-to-be-discovered galaxies). Should this come to describe you, you might start to see the appeal of a woman with more to say than those "three little words" -- "Uh-huh. Uh-huh. Uh-huh."

My new boyfriend is sweet, successful, and handsome, and he rocks my world in bed. The problem? I'm 5'8", and he's 5'6". I'm embarrassed to admit this, but I'm just not that attracted to him when he's standing up.

--Shallow

Women like things that are tiny and cute, so it's been kind of a trend to go around with a little dog poking out of your purse. Sadly, dressing your itsy-bitsy boyfriend in a sailor shirt and sunglasses and tossing him in your handbag has yet to catch on.

Okay, 5'6" isn't exactly itsy-bitsy -- but it might as well be to you. Your preference for taller men -- which biological anthropologist Boguslaw Pawlowski finds 89 percent of women have -- didn't come out of nowhere. Tallness in a man suggests an ability to protect a woman and is associated with social status and access to resources. It also suggests good genes, because ancestors who weren't starving to death and riddled with parasites would have had the metabolic resources to put toward growing tall.

People say looks shouldn't matter -- which doesn't for a moment change the fact that they do. Clearly, shortness is a deal breaker for you. This doesn't make you "shallow." It makes you somebody who should stop dating short guys -- ideally before you blurt out your true feelings in bed: "Grow, Bradley!...I mean, 'Oh...Bradley!'"

Four months ago, I started hooking up with this hot guy I met on Tinder. He isn't someone I'd normally go for; he's a total mess and serious trouble. He always made me come to his place, and I always left feeling gross rather than satisfied. However, about once a month, I'd feel attached and confess this to him. He'd go into hiding, but he always came back for sex. The whole thing made me worried, anxious, and sad, so I deleted his contact info, but I miss him and think about him constantly. How do I stay strong? If he texted me, I'd just run back to his bed.

--Detoxing

Sex that turns your stomach is a small price to pay for romance, like a man whispering sweet nothings in your ear: "Just leave your coat on. This won't take long."

Yes, it's pretty amazing to find yourself missing a man you dislike and maybe even despise. This probably comes out of how there's a potentially higher price for women from naked fun -- ending up with a sex dumpling (uh, child) -- and whoops, where did that Hunky McHunkington run off to, now that the kid needs food, diapers, and a college education?

Because women can get "impregnated and abandoned," anthropologist John Marshall Townsend explains, female emotions evolved to act as an "alarm system" to monitor the "quality and reliability" of male investment and "remedy deficiencies even when (women) try to be indifferent to investment." In a study of Townsend's I've referenced before, even when women wanted nothing but a shag from some dude -- basically seeing him as useful meat -- they often found themselves fretting the morning after about whether he cared about them or only wanted sex.

These women aren't mushy-minded idiots. Chances are, they've been roofied into these feelings -- by their own bodies. Oxytocin -- a hormone associated with emotional bonding -- gets released in both men and women through cuddling, kissing, and orgasm. However, men's far greater supply of testosterone -- especially when they aren't in a committed relationship -- can act as a sort of nightclub bouncer, blocking the uptake of oxytocin.

As for the monthly pull this guy has on you, research by evolutionary psychologists Kelly Gildersleeve and Martie Haselton suggests that once a month -- during ovulation -- a woman seeking casual sex is more likely to be drawn to a cad's more masculine features (like a square jaw and a muscular build). As for how you might quit this particular cad, let's get real. Deleting somebody's number doesn't stop them from calling. You've got to block his number. You might also use free smartphone apps -- like Productive, to motivate yourself by ticking off the days you've gone cadless, and Clue, to track your ovulation. For added fortitude, make a list of the ways sex with him makes you feel. Being worried, anxious, sad, and grossed out can sometimes be a reason to get a man over pronto -- but only if he's a miracle worker of a plumber.

I've been in love with my former high-school teacher for five years. We grew close when I was a student, but nothing physical happened. I'm now an adult, and we talk frequently (and rather flirtatiously) on the phone. I would pursue him if he weren't married, with a family. Now I just need to admit my feelings to him and ask what his intentions ever were. I refuse to believe that he finds our constant chats to be completely innocent, and I don't think I can go on without telling him how crazy he's making me.

--Smitten

When somebody at a cocktail party asks the guy "What do you do?" his answer isn't supposed to be "My former students."

Sure, you're now an adult. Unfortunately, he's still a husband. But never mind that; you've got feelings clawing to get out. And that is a problem. James Pennebaker, who researches emotional expression, explains that "actively holding back or inhibiting our thoughts and feelings can be hard work." It causes a lot of tension -- which is uncomfortable, making you long to release your pent-up feelings. In other words, a crushing need to be "honest" isn't necessarily courageous or noble. It's the psychological version of needing to pee.

As for how Mr. Homeroom feels, probably like a guy whose wedding vows are supposed to trump "hot for teacher." Luckily, there's a simple way to avoid the impulse to tell him "how crazy" he's making you: Cut off all contact. No doubt, it can be a highly rewarding thing for a teacher when his life is changed by a student -- except if that change is from happily married daddy to miserably separated dude living in his kids' backyard playhouse.