If you open the Handbook of Clinical Sexuality for Mental Health Professionals — a book often considered the bible of sex therapy — you will find a scholarly list of more than 100 different fetishes or paraphilias, as clinicians term them. They include acrotomophilia (attraction to amputees), emetophilia (arousal from vomiting), and katoptronophia (arousal from mirrors). Not to be outdone, a 2009 work on criminal and unusual sexual practices contains a presumably exhaustive list of more than 500 paraphilias, adding allotrioasty (attraction to people of other nations) and eproctolagnia (attraction to flatulence).
Paraphilias have been a clinical concept for more than a century, with several specific paraphilias identified in Krafft-Ebing's pioneering 1886 monograph Psychopathia Sexualis, including sadism, bestiality, and the whipping of boys. There have also been non-academic attempts at categorizing the apparent cornucopia of fetishes. For example, Deviant Desires author Katherine Gates crafted a rather byzantine and idiosyncratic fetish map:
So what are to make of all these contemporary catalogs of paraphilias? Surely the breadth of these lists reflect a century's worth of scientific inquiry into the variety of human sexual preferences? These impressive Latin appelations must be based upon careful investigations into the prevalence and origins of this apparent cornucopia of sexual deviancy, right?
When we embarked on our own research into the sexual brain, one of our explicit goals was to determine if online behavioral data could enhance our knowledge of the distribution and prevalence of fetishes. Our starting point was the clinical lists of paraphilias. We presumed scientists already had a pretty good understanding of paraphilias, their origins, and especially their frequency in the population — especially considering that specific paraphilias are listed in the current edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-4R) and will remain in the DSM-5.
We analyzed almost a billion Web searches; hundreds of thousands of individual search histories; the 42,337 most popular adult websites, including all the most popular sites devoted to specific paraphilias; internal data from several adult websites including PornHub (at the time, the most popular tube site); a million erotic stories; the tags, ratings, and hits on millions of pornographic videos; and several other large, cross-cultural online data sets. We used them to measure the presence of acrotomophilia, emetophilia, katoptronophia, and all the other unpronounceable paraphilias.
It didn't take much analysis to realize that both the scholarly and popular catalogs of paraphilias bore little resemblance to reality. The online behavioral data simply did not match clinical accounts. The academic literature did an awful job of predicting the distribution of sexual interests in a cross-cultural sample of hundreds of millions of people. Popular predictions by ordinary folks, including sexual activists, weren't any better. The stunning divergence between the clinical conceptualization of paraphilias and first empirical window into their actual presence in the population eventually became too significant to ignore. As a result, we've come to believe that the terms "paraphilia" and "fetish" should go the way of terms like "retarded," "spastic," and "hysteria." These terms embody both a derogatory and misguided understanding of the nature of human sexual preference. Men and women do not suffer from "atypical" or "deviant" fetishes, but rather possess a range of typical sexual interests that can mostly be predicted from the natural operation of healthy sexual mechanisms in the brain.
Perhaps the greatest revolution in psychiatry occurred in the 1970s, with the transition from the second edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM2) to the third edition (DSM3). This also marked the transition from unreliable, low-validity, non-evidence-based categories of mental disorders (mostly influenced by psychoanalytic theory) to reliable, high-validity, symptom-based categories of mental disorders (mostly adopted from research-based criteria from psychiatrists at Washington University in St. Louis.) Until the Internet, most scientific understanding of paraphilias was based upon one-off case studies from individual clinicians (such as John Money's fascinating account of formicophilia) and small samples of patients at clinical institutions. Reliable prevalence numbers were impossible to come by; in fact, Kinsey's surveys from the 1950s have remained the only systematic quantification of paraphilias in a large, non-clinical population, though his samples were convenience-based and mostly middle-class Caucasians from the mid-West and northeast of the USA. Theories about paraphilias lacked coherence and predictive power. In other words, the classification of paraphilias has been closer to the diagnostic criteria of the DSM2 than the DSM3.
How did online data stack up to the clinical catalogs of paraphilias? Most of the paraphilias (e.g., katoptronophia, teratophilia, pygmalionism, symphorophilia, formicophilia) were exceedingly rare on the Web. (Though eproctolagnia showed up in the website Fart Fantasy, "The Premier Female Fart Fetish Website Full of Hot Girls Who Love to Blast Gas!") At the same time, the clinical, scientific, and cultural literature all failed to predict those sexual interests that are very common, such as gynandromorphophilia (an interest in shemales), phallophilia (an interest in penises; or, perhaps more precisely, humongousphallophilia), and schediaphilia (an interest in animated characters). Other clinical "paraphilias" seemed to reflect a misinterpretation of a sexual interest, such as the venerable but poorly understood clinical concept of sadomasochism (which frequently mistakes an interest in domination/submission power exchanges for an interest in pain) and zelophilia — "getting aroused by jealousy," which is almost certainly a manifestation of sperm competition adaptations triggered by a partner's unfaithful behavior rather than sexual arousal from the jealousy itself. (The clinical literature also failed to predict the immense cross-cultural popularity of sexual arousal from unfaithful partners, one of the most common sources of male arousal.)