If the supermodel Kate Upton were to walk into my office right now and tie me to my chair before doing a slow striptease and depositing her vagina in my face, I think I'd require therapy for years. But if this identical event were to happen to my heterosexual brother or to one of my lesbian friends, I suspect their brains would process such a "tragic" experience very differently. And my not-very-amused sister-in-law would see my brother's encounter with said vagina differently still.

A universally objective reality simply doesn't exist in the sexual domain; what's harmful to me isn't necessarily harmful to you, and vice versa. It will change as soon as I put this comma right here, but as of this very moment, there are exactly 7,088,343,858 people on the planet. If all but one of these individuals were to experience harm in exactly the same way from a certain sex act, that solitary person is nevertheless just as right (or just as wrong) as all the others combined. This is because there's no "correct" way to experience a sex act, only individual differences in subjective realities. It may be a moot point, since it's not logic that guides culture but instead sheer social mass shouldering into it with brute force, but nonetheless 7,088,343,857 shared subjective realities do not add up to a single objective fact. What was harmful to them was not harmful to him, and that, as they say, is that.

That's all well and good, you might point out, but there are issues here far more serious than two people disagreeing over whether, say, getting tied up and forced into Kate Upton's crotch is sexy or cruel. Take sex between adults and minors, for instance. Is harmfulness "subjective" with that, too? Well, yes and no. This is a dark and treacherous path that we're about to embark on, so it's all the more important for us to be guided by the light of clear thinking. There's no doubt whatsoever that children who are sexually abused are often irreparably damaged—and not only psychologically but, sadly, physically as well. As the recent Montana case of a teenage girl who committed suicide after a much older teacher sexually assaulted her (for which he was sentenced to a measly month in jail) sadly attests, denying that children can face grievous, debilitating, and permanent harm from being violated by manipulative adults in this way is just asinine. It flies in the face of scientific data showing such trauma, for many, is all too real. Yet, an inconvenient fact is that research has also revealed that not every minor who has a sexual encounter with an adult is traumatized.

One important thing to highlight here is that when it comes to sex, there's a world of difference between a 6-year-old and a 16-year-old. (The term "pedophilia" has become so misused that it's now difficult to reclaim its proper scientific meaning from the vernacular, but this area of what the sexologist John Money called the "chronophilias" gets fairly complex.) A 6-year-old child may subjectively experience little, if any, harm at the time of being molested by an adult, but that doesn't mean significant damage hasn't been done. As the child grows older, his or her interpretation of the experience on coming to understand what really happened may become increasingly traumatizing. One way to think about it is that the sexually abused child has essentially been implanted with a psychological time bomb that may or may not go off down the road. There's a marginal chance that it won't detonate at all, but if it does, it's often catastrophic. This can also be the case with teens (many of us have regrets about being taken advantage of when we were young and naive, sexually or otherwise), but for a 16-year-old who has hormonally fueled desires that are just as intense as those of the adult he's having an encounter with, it's a very different can of emotional worms.

The more controversial "yes" part of my response to the question of whether the harm in such sexual encounters is subjective, therefore, refers to the fact that for some individuals looking back on their childhood or adolescent experiences, the event was not harmful to them. For whatever reason, their bombs never went off. Whether or not we have a hard time understanding their perspective, there are indeed people out there who feel this way. (And some who, believe it or not, even view their sexual encounter with an adult positively.) The "no" part of my response, by contrast, relates to the fact that the child's sexual subjectivity inevitably changes as he or she grows older. To say that a 6-year-old who doesn't understand what's happening to her isn't being harmed because she appears to be just fine otherwise, or even that she "likes it" (as deluded child molesters sometimes claim), is to miss the point entirely of these delayed, and potentially devastating, emotional injuries that may affect her later. If we were to follow up with this little girl in 20 years, we might find a woman damaged beyond repair by the memories of the very events that were inconsequential to her at the age of 6. In other words, the bomb has gone off. So, again, although harm may not be inevitable in every case, what is inevitable is the very high risk of shattering a child's life for the sake of one's own immediate sexual gratification.

When it comes to adolescents' sexual experiences with adults, where the distance between the subjective present of the child and his or her subjective future has grown narrower, some researchers believe that the damage isn't as significant as it's often assumed to be. Bruce Rind, for example, an expert on the study of "intergenerational sexuality," set off some explosions of his own in the late 1990s when he published a set of highly contentious (to put it mildly) findings to this effect. The best predictor of subjective harm—past, present, and future—he found, is the minor's lack of consent. Obviously, there's consent in the legal, underage sense of the term, but there's also consent as a mental state (basically, the feeling of wanting to do something) that occurs regardless of age. Rind was more interested in this latter, psychological meaning. In 1998, he and his coauthors, Philip Tromovitch and Robert Bauserman, managed to put the American Psychological Association (which is composed mostly of academic, research-oriented clinical psychologists) in the rather awkward position of having to publicly acknowledge that not every incident of an adult having sex with a juvenile is harmful. Actually, "awkward" may not be entirely the right way to describe it—it was more that the APA locked horns with every wrathful, powerful politician in the country for defending this very politically incorrect view.

It all started when Rind and his colleagues published a study in the association's flagship journal, Psychological Bulletin. The authors argued that it makes little sense to refer to something as "child sex abuse" if, as an adult, the individual doesn't personally feel harmed and if his or her harm can't be detected by any known empirical measures. The most delicate issue for the APA was that this wasn't just the authors' personal and controversial opinion, but a statement based on scientific findings. Rind's study was a meta-analysis of previously published data on the sexual histories of a whopping 35,303 college students from around the world. One thing that set his project apart from most others in the field of child sex abuse was that the data being evaluated wasn't from clinical samples of adults who'd sought help for ongoing problems stemming from their being raped, molested, or otherwise sexually exploited as children or teenagers, but from random samples of college students. And what Rind and his coauthors found by using a large nonclinical sample was that the majority of those people who reported having had consensual encounters with adults as minors were, at the time of testing, no more likely to have pervasive psychological problems than those who hadn't.

Now, it's extremely important to bear in mind that for the most part, these mentally healthy individuals weren't those who'd been subjected to terrible abuses as children. More often they were those who, as adolescents, had consensually (again, in the psychological sense of that term) "fooled around" in various ways with someone on the other side of the legal line (wherever that line had been drawn at the time, since, remember, it was an international sample and, as we'll be examining in detail shortly, the legal age of consent varies by country).

I never had any such experience with an adult while growing up, so it's hard for me to know for certain. But speaking only for myself, I suspect that had a very adult Mr. April 1991 stepped out of the calendar that hung in my sister's dorm room that year, ripped, hairless legs beaded with river water, his unkempt hair plastered against his forehead and glistening clavicles, wearing nothing but wild green eyes and a tapioca-colored fishnet loincloth (my vague recollection), and proceeded to gently guide me on the ways of man-on-man love, the last thing that my 15-year-old self would have felt was harmed. I only wish I had such a memory to look back on now. On the other hand, had he forced himself on me, I could be a quivering pile of jelly right now. But the point is that even when it comes to illegal sex with a minor, the likelihood of psychological harm is reduced by the minor's consenting mental state.

You might think that Rind and his fellow investigators had a dark agenda of some sort (and certainly many critics have accused them of such), but in fact they were exceedingly careful to note that their findings shouldn't be used to implement any policy changes to existing laws concerning underage sex. Rather, their intention was only to call into question some widely held assumptions about the universal harmfulness of such developmental experiences.

But then the conservative radio talk-show host Dr. Laura Schlessinger (whose PhD, incidentally, is in physiology, not psychology, not that she's ever let that get in the way of giving mental-health advice with a side of Old Testament gloom) somehow got wind of it and proceeded to stir up a bit of a hornet's nest by complaining about Rind's "junk science" and pedophilia apologia to listeners of her nationally syndicated program. That incendiary development, combined with NAMBLA's (the notorious North American Man/Boy Love Association) gushing over Rind's findings on its website, quickly escalated into outright chaos. Before long, some members of Congress learned of the study (whether that was from being regular listeners of Schlessinger's show or from being loyal followers of NAMBLA is hard to say).

By the spring of 1999, Alaska, California, Illinois, Oklahoma, Louisiana, and Pennsylvania had passed official resolutions executively condemning Rind's scientific findings. On July 12 of that same year, in an incident without precedent in the history of psychology, the US House of Representatives convened to establish Resolution 107, in which 355 members of the House (all of whom were even less qualified than Dr. Laura Schlessinger to evaluate a study in psychological science) legislatively lampooned Rind's empirical work by declaring—data be damned—that any and all sexual relations between minors and adults were categorically abusive and harmful. Just a few weeks later, the Senate passed this anti-Rind resolution by a unanimous "Hear! Hear!" voice-vote margin of 100 to 0. (No senator would dare to go against the grain and kiss any future political aspirations good-bye by being known as the one pervert voting in favor of Rind's findings.) One of the few politicians to abstain from voting on the study was Representative Brian Baird, a Democrat from the state of Washington who boasted a PhD in clinical psychology. Baird wanted to go on record as saying that out of the 535 members of the House and Senate, only 10 had actually bothered to read Rind's article. The advisory board members of the APA, meanwhile, butted heads with these suits in Washington, DC, over the fallout. After all, the former were in the business of science, not moralizing. They staunchly defended the Psychological Bulletin editor's decision to publish the study in their prestigious outlet. Moreover, the study had been carefully vetted—and ultimately recommended for acceptance—by other experts in the field.

The Rind data remains polarizing, with some researchers still questioning his methods and motives, and others, in turn, questioning their motives for questioning his. Given the brouhaha, scholars on both sides of the debate left things for a while on a "Let's just agree to disagree" note (which essentially meant cursing each other under their breath and taking a break from duking it out in public). But in 2006, the psychologist Heather Ulrich replicated the 1998 findings, concluding cautiously that the presumption of universal harm from juveniles having a sexual encounter with an adult is too simplistic to account for the variance in people's subjective interpretations of their own life experiences.

Now, ostensibly, there's no good way for one to lean on this hot-button issue. If you conclude from Rind's findings that having sex with minors is "sometimes okay," then to many people you'll sound like an advocate of child molestation. Yet if you still get red in the face and believe that anyone having sex with a minor is manipulating an innocent child, then you're glossing over all the gray areas. Much of the disagreement, I think, stems from our failure to define our terms. When, exactly, does "childhood innocence" end? Most of us have some vague sense of once having had it—or at least something like it—but how does one quantify or even standardize such an abstract construct? At what precise moment in time, for instance, did you lose yours? Perhaps you never had it, or perhaps you never lost it.

Few of us are so naive as to believe that it happens at the stroke of midnight, dividing childhood from legal adulthood, especially given that such a line is culturally arbitrary. There are a lot of uncomfortable philosophical problems with age-of-consent laws that continue to lead to people, including teenagers themselves who have sex with someone just a few years younger, being treated unfairly in our society. It's only when it comes to sex that on some mandated calendar day the legal concept of "consent" changes so abruptly from being a chronological state to a mental state. Having sex with a person before the bell tolls on that day, even if it's the minor who makes the first move and you're but the target of his or her passionate underage desires, will change you abruptly into a criminal sex offender. Whatever was going on inside the minor's head is usually seen as inconsequential.

In other legal contexts, however, minors are tried as adults precisely because of what was going on inside their heads at the time. A 16-year-old boy who rapes a woman after she rejects his solicitous advances would typically be punished as an adult. But if a woman encourages a solicitous 16-year-old boy after he tries to kiss her, he'd be regarded by criminal prosecutors as a child victim. In other words, legally, the minds of minors matter only when they've caused adults sexual harm; their mental states are inadmissible in court when they cause adults sexual pleasure. I don't know about you, but to me there's an unsettling tension in the logic between these contrasting scenarios.

Age-of-consent laws are admirably meant to protect adolescents from being sexually exploited by adults (and there are, sad to say, plenty of the latter for parents to be concerned about). But there are problems with a hard-line approach to this emotional immaturity argument as well. One might be stigmatized for doing so, but it's perfectly lawful to have sex with consenting adults who have the intellectual and emotional capacity of an underage child. To take a rather extreme example, the average mental age of an adult with Down syndrome is 8, yet unlike having sex with a 17-year-old equipped with a three-digit IQ, being with someone with this or any other developmental delay isn't a crime, so long as the person is 18 years of age or older and "consents." So if we're really trying to protect the vulnerable from sexual harm due to their mental immaturity, then using chronological age, rather than mental age, to draw the legal line seems a somewhat odd way to go about it. I can assure you after an early dating mishap with one particular—to put it both kindly and mildly—intellectually blunt grown man, these are often orthogonal measures.

Recent work by the cognitive neuroscientist Sarah-Jayne Blakemore shows in fact that there's no hard-and-fast threshold at which a person crosses over into a clear brain-based psychological adulthood. The prefrontal cortex, arguably the neuroanatomical region most relevant to sexual decision making due to its executive role in long-term planning abilities, empathy, and social awareness, doesn't stop growing until we're in our mid-30s. For some, it's still developing well into the fifth decade of life.

Those who want to have sex with minors often cite in their defense the cultural arbitrariness of ages of consent. But they're at least right about that, and these numbers are in perpetual flux even within cultures. The first such age-restricting statute, Westminster I, appeared about seven centuries before the popular TV series To Catch a Predator first aired, in the year of our Lord 1275, under the heading of a broader rape law in England. According to this new legislation, any man who dared to "ravish" a "maiden within age," with or without her consent, was guilty of a misdemeanor. English legal scholars interpret the phrase "within age" to mean the age of marriage, which at the time was 12. Had the man been married to this same 12-year-old girl, in other words, this age-based rape statute wouldn't have applied. In the centuries that followed, similar edicts meant to protect children (namely girls) from sexual abuse or exploitation by adults (namely men) started to dust the globe. And wide variations in the age of consent are written across this historical landscape.

In the 16th century, for example, the North American colonies adopted from Britain the age of 10 as the appropriate cutoff, and this remained in the formal legislatures of 37 US states until long after the Civil War. Of the other existing states in the 1880s, only nine had by then decided that the "advanced age" of 12 was probably a more reasonable number. (One state, Delaware, had even lowered its cutoff to a mind-boggling 7.) Only in the late 19th century was the age of consent raised to 16 throughout most of America, a concession by the social reformers who had spearheaded the campaign and had initially sought to have it changed nationwide to 18, which they'd largely accomplish by 1920. Some in the growing feminist movement even hoped to raise it to 21, the age at which women could legally inherit property. Today, each state has its own numerous and complex series of clauses dealing with factors such as age differences between parties and the nature of specific sexual acts, but general ages of consent presently range from 15 (in Colorado only) to 18.

Tidal changes were happening with Europe's age-of-consent laws over this long time span as well. With the Enlightenment really coming into bloom in the 18th century, the philosopher Jean-Jacques Rousseau's influential ideas on childhood spread throughout France and beyond. His portrayal of children as social tabulae rasae, or "blank slates," lasted well into the Napoleonic era and replaced the archaic notion of kids as adults in miniature. Inspired by Rousseau, public sentiment came to hold that children were intrinsically pure and became tainted only by the corrupting influence of society. Rousseau also marks the dawn of developmental psychology and the implementation of age-segregated education. Children and teenagers were now seen as having qualitatively different kinds of minds from grown-ups, marching through what Rousseau believed was a universal pattern of cognitive and emotional stages. (Development wasn't just a matter of acquiring more and more facts, in other words, but the very way in which one processes information and perceives the world changes over time as well.) Yet even at the peak of this radical new moral Enlightenment, the sexual readiness of children was, strangely enough, apparently seen as a separate issue. The age of consent in France during this whole time was a mere 11, getting bumped up to 13 only in the year 1863.

By the late 19th century, 13 had also been chosen as the carnal threshold in other European nations, including Portugal, Switzerland, Spain, and Denmark. Today, Spain is the only country in the region to keep 13 as its age of consent, with other nations variously lifting theirs to 14, 15, or 16, at most. Deplorable tales of child prostitution during the industrial revolution spurred moral reformers in England and Wales, meanwhile, to raise the age of consent across the British Isles from 13 to 16, a social cause to combat child exploitation that had also reverberated in the American age-of-consent campaign mentioned earlier.

Similarly wobbly views on sex and adolescents—or rather sex with adolescents—are on profligate historical display elsewhere. It goes in the opposite direction, too. The age of consent in 1920s Chile was 20, but now it's 16. A century ago in Italy, it was 16, too. But today it's 14 there. Overall, studying the numbers in even the most contemporary international age-of-consent table will give you the impression that you're looking at a flurry of seemingly random digits between 12 and 21 (a sizable range): It's 13 in Argentina, 18 in Turkey, 16 in Canada, 12 in Mexico, 20 in Tunisia, 16 in Western Australia, 15 in Sweden, and so on. "More than 800 years after the first recorded age of consent laws," writes the historian Stephen Robertson, "the one constant is the lack of consistency."

Just as when we're assessing religions with conflicting theologies, we can draw only two possible conclusions from Robertson's observation: Either some societies have the one true age of consent and every other has therefore got it wrong, or any given society's age of consent is based on what its citizens have simply chosen to believe about human sexuality and psychological development. And similar to what any objective analysis of competing religious beliefs would force us to conclude, there's no evidence that the former is the case for cultural variations in age of consent laws (that there is "one true age") and every reason for us to conclude the latter is in fact what we're dealing with. recommended

Jesse Bering is a psychologist and frequent Savage Love guest expert. This essay is excerpted from his forthcoming book, Perv: The Sexual Deviant in All of Us, to be published October 8 by Scientific American / Farrar, Straus and Giroux. Copyright 2013 by Jesse Bering. All rights reserved. Bering reads from the book on Monday, October 14, at Town Hall.