Wednesday, September 25, 2019

Differences in the genetic architecture of cognition?

Tableau III, Piet Mondrian (1872-1944). The polygenic score can provide a measure of innate cognitive ability in various human populations. However, it is less valid for African Americans, apparently because of differences in the genetic architecture of cognition.

When IQ is measured in European Americans and African Americans, the two groups differ on average by about 15 points. Is the difference genetic? Or is it due to different environments?

After years of debate, we are coming close to an answer. The weight of evidence is shifting, especially because of two unrelated developments: 

- We can now easily measure ethnic ancestry by means of genetic data. Previously, we had to rely on self-report or indirect measures like skin color.

- We can now measure the genetic component of cognitive ability: the polygenic score. This score is a summation of alleles associated with high educational attainment. Initially a crude measure, it is getting better and better as we identify more and more of these alleles.

Both research tools were used in a recent study. Lasker et al. (2019) applied them to the Philadelphia Neurodevelopmental Cohort, a sample of 9421 individuals from the Philadelphia area who received medical care from the Children's Hospital of Philadelphia network. They ranged in age from 8 to 21 with a mean of 14.2. They were 51.7% female, 55.8% European American, 32.9% African American, and 11.4% other. All of them were genotyped and given a series of cognitive tests.

This dataset had advantages over those of previous studies:

- All participants came from the same geographic area. 

- Heritabilities of cognitive ability were already estimated by another research team, specifically 0.61 for the African American participants and 0.72 for the European American participants.

- Skin, hair, and eye color could be estimated from the genetic data to control for the effects of "colorism" (discrimination favoring lighter-skinned over darker-skinned African Americans)

- Polygenic scores could be calculated from the genetic data

The main disadvantage was the participants’ young age. Before adulthood the brain is plastic and still developing, so the heritability of cognitive ability is lower. 

IQ results

IQ scores were 100 for European Americans, 98 for self-described biracial Americans, and 85 for African Americans. The three groups were respectively 99% European, 80% European, and 19% European.

African Americans only

European admixture significantly correlated with IQ among the African American participants. The correlation remained significant after controlling for either skin color or socioeconomic status. Interestingly, skin and hair color didn't significantly correlate with IQ independently of European admixture, but eye color did. Brown eyes correlated positively with IQ. No explanation was offered by the authors. Did they get the same finding with European Americans?

Biracial Americans only - smarter than expected

As with African Americans, skin color didn't seem to influence intelligence independently of European admixture. On the other hand, "biracial status had a significant effect independently of European ancestry." In other words, racially mixed individuals who identified equally as African American and European American, and not just as African American, tended to be more intelligent than what their degree of European admixture would predict. 

The term "biracial" as a badge of identity is recent and seems to be most popular among middle-class people: 

Interestingly, many of the respondents here who identify as biracial are middle class, educated in private schools, and raised in predominantly white neighborhoods with mostly white social networks (Rockquemore and Brunsma 2008, p. xxii)

It may be, then, that self-identified "biracial" people have parents who are, on average, of higher quality than other people of the same racial background.

African Americans, Biracial Americans, and European Americans combined

When all three groups were combined, the most important factor was European admixture. Next came socioeconomic status, which correlated with cognitive ability independently of European admixture. Finally, self-identification as a European American had an effect over and above that of European admixture. The last factor suggests that European American culture has a positive influence on cognitive ability.

Polygenic score results

The polygenic scores ran into a problem that others have noted: the genetic architecture of cognition seems to be different in African Americans. This is a problem because researchers have used only Europeans or European Americans to identify genetic variants that are associated with high educational attainment. Those variants did correlate with cognitive ability in the African American sample, but to a much lower degree than in the European American sample. Their validity as a measure of cognitive ability was only 20% of what it was in the European American sample.

The authors used a subset of the same variants to create a polygenic score that would be less sensitive to linkage disequilibrium decay and thus more valid across different human populations. This polygenic score had good validity in both the African- and European-American samples (r = 0.112 and r = 0.227 respectively).

The authors then tried to create an even better polygenic score by excluding variants that are rare in African Americans. There was no effect on the results for either African Americans or European Americans. But what about the reverse? Perhaps cognitive ability is improved by some variants that are rare in European Americans but common in African Americans.


This is an excellent study, on a par with the Minnesota Transracial Adoption Study (Frost 2019). The main problem is the participants’ young age. Had adults been used, there would have been less noise in the data, and the results would have been better.

Another problem is the apparently different genetic architecture of cognition in people of sub-Saharan African origin. Piffer (2019) has noted that polygenic scores underestimate African American IQ. He disagrees, however, with the "different genetic architecture" hypothesis, pointing out that no divergence exists between mean population IQ and the polygenic scores he has calculated for various sub-Saharan African groups (Esan, Gambians, Luhya, Mende, Yoruba). None of them, however, are Igbo, and the Igbo are really the one group that stands out from other West Africans on measures of intellectual and educational attainment (Frost 2015a, 2015b). They also contributed to the gene pool of African Americans: "Many of the enslaved Igbo people in the United States were concentrated in Virginia's lower Tidewater region and at some points in the 18th century they constituted over 30% of the enslaved black population" (Wikipedia 2019).

While the polygenic score is a good measure of raw cognitive ability in most humans, we need to develop a modified version for people whose ancestry comes primarily from sub-Saharan Africa.


Frost, P. (2015a). The Jews of West Africa? Evo and Proud, July 4 

Frost, P. (2015b). No, blacks aren't all alike. Who said they were? Evo and Proud. October 10. 

Frost, P. (2019). IQ of biracial children and adults. Evo and Proud. March 10.

Lasker, J., B.J. Pesta, J.G.R. Fuerst, and E.O.W. Kirkegaard. (2019). Global ancestry and cognitive ability. Psych 1(1) 

Piffer, D. (2019). Evidence for Recent Polygenic Selection on Educational Attainment and Intelligence Inferred from Gwas Hits: A Replication of Previous Findings Using Recent Data. Psych 1(1): 55-75  

Rockquemore, K.A. and D.L. Brunsma. (2008). Beyond Black. Biracial Identity in America. Lanham: Rowman & Littlefield Publishers.

Wikipedia. (2019). Igbo Americans

Wednesday, September 18, 2019

Have we been selected for long-term thinking?

GDP per capita as a function of future orientation (Preis et al. 2012)

To what degree do we value the short term over the long term? The answer varies not only from individual to individual but also from society to society. Hunter-gatherers, for instance, value the short term. Perishable food cannot be stored for future use and, in any case, is not normally obtained in large enough amounts to make storage worthwhile. If a hunter gets more meat than his family can consume, he'll give it away to others in the local band.

There are exceptions, especially at northern latitudes. Meat can be stored in caches during winter and in cold lake waters during summer. With limited opportunities for food gathering, women specialize in technologies that need more cognitive input and longer-term thinking, like garment making, needlework, weaving, leatherworking, pottery, and use of kilns. Finally, men hunt over longer distances and therefore plan over the longer term. Northern hunting peoples thus broke free of the short-term mental straitjacket imposed by hunting and gathering. In time, their descendants would spread south and rise to the challenges of social complexity (Frost 2019).

Those northern hunting peoples were better able to exploit the opportunities created by farming, but the transition from one lifestyle to the other was still far from easy. Farming requires not only longer-term thinking but also less monotony avoidance and higher thresholds for expression of personal violence. In recent times, hunter-gatherers usually refused offers to be settled on farms. They saw farming as akin to slavery.

The change in mindset didn't end with the transition to farming. There were different types of farming, and some required longer-term investment than others. Those types generated stronger selection for future orientation.

Language as a mirror of cultural evolution

Galor et al. (2018) argue that language is a mirror of cultural evolution. It can show a society’s degree of commitment to a long-term mindset, as well as other psychological traits.

The periphrastic future tense

The authors studied the relationship between future orientation and forms of the future tense that express intention and obligation, rather than simply prediction:

Languages differ in the structure of their future tense. In particular, linguists distinguish between languages that are characterized by an inflectional versus periphrastic future tense [...]. Inflectional future tense is associated with verbs that display morphological variation (i.e., a change in the verb form that is associated with the future tense). In contrast, periphrastic future tense is characterized by roundabout or discursive phrases, such as `will', `shall', `want to', `going to' in the English language [...] (Galor et al. 2018, p. 6)

[U]nlike the inflectional future tense, the periphrastic future tense is formed by terms that express a desire, an intention, an obligation, a commitment as well as a movement towards a goal. In particular, in the English language, "shall has developed from a main verb meaning 'to owe', will from a main verb meaning 'to want', and the source of be going to is still transparent" [...]. Moreover, "intention and prediction are most commonly expressed by the periphrastic future, while the synthetic one is more common in generic statements, concessives, and suppositions" [...]. Inflectional futures "also appear systematically (often obligatorily) in sentences which express clear predictions about the future (which are independent of human intentions and planning), whereas less grammaticalized constructions [i.e., periphrastic] often tend to be predominantly used in talk of plans and intentions - a fact which is explainable from the diachronic sources of future tenses" [...] (Galor et al. 2018, p. 6)

Galor et al. (2018, p. 16) used pre-1500 AD data to estimate the return on agricultural investment ("crop return") in the homeland of a language’s speakers. They found a positive correlation between this return on investment and the existence of a periphrastic future tense. They concluded that "a one standard deviation increase in crop return in the language's contemporary homeland is associated with a 6 percentage points increase in the probability that the language is characterized by a periphrastic future tense."

Using the World Values Survey, the authors also found a positive correlation between the existence of a periphrastic future tense and future orientation. The correlation held true both for the people of the world as a whole and for Old World peoples who speak languages originating in the Old World (Galor et al. 2018, p. 23).

Interestingly, the return on agricultural investment did not correlate with other linguistic characteristics, like the existence of the past tense or the perfect tense, the existence of possessive classifications, the existence of coding for evidentiality, the number of consonants, and the number of colors (Galor et al. 2018, pp. 18-19).

Grammatical gender

The authors also looked into the relationship between grammatical gender and the sexual division of labor in a language's homeland:

Further, consider ancient civilizations that had been characterized by a sexual division of labor and consequently by the existence of gender bias. Linguistic traits that had fortified the existing gender biases have plausibly emerged and persisted in these societies over time. In particular, geographical characteristics that had been associated with the adoption of agricultural technology that had contributed to a gender gap in productivity, and thus to the emergence of distinct gender roles in society (e.g., the suitability of land for the usage of the plow […]), may have fostered the emergence and the prevalence of sex-based grammatical gender in the course of human history. (Galor et al. 2018, p. 2)

Galor et al (2018, p. 24) found a negative correlation between grammatical gender and “plow negative” crops (i.e., crops not requiring use of the plow and, hence, requiring less male participation). A one standard deviation increase in the potential caloric yield of plow negative crops was associated with a 13 percentage point decrease in the probability that the language has grammatical gender.  The correlation was reversed in the case of all crops, the caloric yield now being associated with a 17 percentage point increase in the probability that the language has grammatical gender.

Politeness distinctions in pronouns

Finally, Galor et al. (2018) looked into the relationship between politeness distinctions in pronouns and ecological diversity, which they related to the emergence of hierarchical societies.

Linguistic traits that had reinforced existing hierarchical structures and cultural norms had conceivably emerged and persisted in these stratified societies in the course of human history. In particular, politeness distinctions in pronouns (e.g., the differential use of "tu" and "usted" in the Spanish language, "Du" and "Sie" in German, and "tu" and "vous" in French) had conceivably appeared and endured in hierarchical societies. Thus, geographical characteristics, such as ecological diversity that had been conducive to the emergence of hierarchical societies (Fenske, 2014), may have contributed to the emergence of politeness distinctions. (Galor et al. 2018, p. 2)

Galor et al. (2018, p. 32) found a significant relationship between politeness distinctions and ecological diversity in a language's homeland. A one standard deviation increase in ecological diversity corresponded to a 15 percentage point increase in the probability that the language has politeness distinctions.

I'm skeptical about the last finding. Is ecological diversity conducive to hierarchical societies? The authors refer to a study that mostly uses African data. More to the point, the study seeks to link ecological diversity to centralized states. Centralization of state power and social hierarchization are not the same thing. Japan, for instance, had a weak central state for much of its history and yet was very hierarchical, as seen in the politeness distinctions of the Japanese language.


Although the authors refer to work by L.L. Cavalli-Sforza, Peter Richerson, and Robert Boyd on gene-culture coevolution, they avoid discussing the possibility that selection for future orientation, gender specialization, and hierarchical politeness has influenced not only culture and language but also human biology. The coevolution they propose is simply between culture and language. It can be summed up as follows:

- Certain patterns of mind and behavior have been favored to varying degrees in different societies.

- These cultural patterns are transposed into language.

- Language then reinforces those cultural patterns: "In light of the apparent coevolution of cultural and linguistic characteristics in the course of human history, emerging linguistic traits have conceivably reinforced the persistent effect of cultural factors on the process of development" (Galor et al. 2018, p. 1).

Language is not a passive mirror of culture. It can also act upon culture. For instance, the way we perceive the future, and its relative importance to us, may be shaped by the way we speak. This is of course the Sapir-Whorf hypothesis.  In a farming society, the periphrastic future tense might make it easier to envision farming methods and technologies that pay off over the longer term. Similar arguments have been made for grammatical gender and politeness distinctions. The way we speak influences our thoughts and behavior.

Again, the authors leave it to the reader to go one step farther: patterns of mind and behavior may influence the frequencies of alleles in the gene pool.


Fenske, J. (2014). Ecology, trade, and states in pre-colonial Africa. Journal of the European Economic Association 12(3): 612-640. 

Frost, P. (2019). The Original Industrial Revolution. Did Cold Winters Select for Cognitive Ability? Psych 1(1): 166-181 

Galor, O., O. Özak, and A. Sarid. (2018). Geographical Roots of the Coevolution of Cultural and Linguistic Traits (November 7, 2018). Available at SSRN: or  

Preis, T., H.S. Moat, H.E. Stanley, and S.R. Bishop. (2012). Quantifying the advantage of looking forward. Scientific Reports 2: 350

Wednesday, September 11, 2019

Why is vocabulary shrinking?

Vocabulary decline in adult non-Hispanic White Americans (controlled for years of education completed)

"Are Americans more intelligent than a few decades ago, or less intelligent?" So asks psychologist Jean Twenge in her introduction to a recent paper on vocabulary decline in Americans. The findings are disconcerting, to say the least:

We examined trends over time in vocabulary, a key component of verbal intelligence, in the nationally representative General Social Survey of U.S. adults (n=29,912). Participants answered multiple-choice questions about the definitions of 10 specific words. When controlled for educational attainment, the vocabulary of the average U.S. adult declined between the mid-1970s and the 2010s. Vocabulary declined across all levels of educational attainment (less than high school, high school or 2-year college graduate, bachelor's or graduate degree), with the largest declines among those with a bachelor's or graduate degree. (Twenge et al. 2019)

The last decline was especially large: more than half a standard deviation. In general, vocabulary test scores have fallen by 8.5%. Ethnic change doesn’t seem responsible, since non-Hispanic whites have had almost the same decline: 7.2%.

So what's going on? The authors considered the explanation they first raised: Americans have become less intelligent despite the increase in education.

First, Americans' vocabularies might be shrinking despite the increase in education. This is plausible given the steep decline in the amount of time high school students spend reading [...] and the decline in SAT verbal scores over time [...]. This explanation could account for the narrowing of abilities between those without high school educations and those with college educations. The difference in vocabulary by education was approximately 3.4 correct answers in 1974-79 but dropped to 2.9 correct answers by 2010-16. However, this explanation would not account for the decline in performance in all educational groups. (Twenge et al. 2019)

Uh, why not? The last sentence makes sense if the explanation is simply that postsecondary education has become less effective. But what if vocabulary has declined because the capacity for learning words and retaining them has also declined? The cause may be genetic. Can we at least ask that question?

Lower admission standards? Mismatch between cause and effect

The authors then consider another explanation: because college admission standards have been lowered, people of lower ability have been going on to postsecondary education in larger numbers; those who don't are increasingly the least able.

If education does not improve vocabulary, but educational attainment increases, those with higher ability will be increasingly selected into the higher education groups, leaving those with lower ability in the lowest educational attainment groups. Thus, the no high school degree group will be left with those of lowest ability, and the college graduate group will have absorbed more with only moderate ability. (Twenge et al. 2019)

That explanation is popular, but it doesn’t really match the findings. The vocabulary decline was steepest during the late 1970s and early 1980s. It then levelled off. A second decline may have begun in 2008, but it’s still too early to say (see Figure 1 reproduced above). Most of the decline doesn't correspond to any previous change in college enrollment by recent high school graduates. The enrollment rate rose slowly from 45.7% in 1959 to 49.4% in 1980. It began to grow faster only in the mid-1980s, breaking through the 60% level in 1991 and the 70% level in 2009 (Bureau of Labor Statistics 2010).

So the alleged cause doesn’t match the presumed effect. The steep increase in college enrollment from the mid-1980s onward could not have caused the steep vocabulary decline during the late 1970s and early 1980s. Keep in mind that most of the GSS respondents had completed their education some years earlier, almost ten years earlier on average. So the average respondent in the late 1970s had to meet college admission standards that existed in the late 1960s.

Most of the decline has been among early boomers

Because the GSS was first administered in 1974, we don't know when the steep vocabulary decline began. But we do know when it ended: in the mid-1980s, among respondents who were born on average thirty years earlier. A genetic cause would imply a rapid deterioration in the gene pool from 1945 to 1955 and a slower deterioration thereafter. I have no idea what that cause could be.

If we're looking for a cultural cause, it would have acted most strongly on the same cohort of "early boomers." Perhaps it was their increasing exposure to TV and their decreasing exposure to high literature. Those cultural changes were already a fait accompli for "late boomers," who experienced a more gradual dumbing down of vocabulary on TV and in print. The post-2008 vocabulary decline, if it’s real, might reflect the growing importance of iPhone texting since the late 2000s.

That cultural explanation has some support from the data and is favorably mentioned by the authors. For one thing, comparison with the results of another test (WAIS) suggests that the decline has been mostly in passive vocabulary, i.e., the words we understand but don’t use spontaneously in speech (Twenge et al. 2019). We’re less proficient in "bookish" language:

Perhaps American culture became less intellectual, either because of or in response to a lowering of verbal ability among those who read books. Authors aim to sell more copies of their books, and thus may adjust their vocabulary level to the skills and preferences of a wider slice of the population. Or, perhaps authors lowered the vocabulary level of their books for some other reason such as an interest in getting out a message without linguistic complexity getting in the way. For example, the Bible has been revised repeatedly to make it more accessible with the King James Version, the most complex and lyrical English language version, being succeeded by the simpler New International Version, Living Bible, and New Revised Standard Version. (Twenge et al. 2019)

The last point rings true. When I was studying Shakespeare in high school my mother could explain words I had trouble understanding. She had never gone beyond Grade 10, but she could read the Bible in the King James Version, as well as a lot of high-brow literature. This was true for many ordinary adults in the 1970s. Today, regular reading of the Bible is unusual and almost always confined to modern English versions.


Yes, college has become a less interesting place for learning vocabulary, and for learning in general. Yes, a big reason is the growing number of students who don’t really belong there, and the consequent lowering of standards. Yes, America’s cultural and linguistic mix is changing, and for that reason alone the average American would have a smaller English vocabulary.

Nonetheless, those factors fail to explain why non-Hispanic white Americans know fewer words today than they did a half-century ago, especially in their passive vocabulary. Something else is going on, and it seems to be a shift away from high literature and toward simpler audiovisual media: TV, video, text messaging …


Bureau of Labor Statistics. (2010). College enrollment up among 2009 high school grads. TED: The Economics Daily. April 28

Twenge, J.M., W.K. Campbell, and R.A. Sherman. (2019). Declines in vocabulary among American adults within levels of educational attainment, 1974-2016. Intelligence 76: 101377

Wednesday, September 4, 2019

Why podophilia?

Before the bath
 – William-Adolphe Bouguereau (1825-1905)

What is it about women's feet? They are the part of a woman’s body that men most often fetishize. A study on the frequencies of different fetishes concluded: "Feet and objects associated with feet were the most common target of preferences [...] We found podophilia prominent (about half of Feticist groups subscribers) in our sample" (Scorolli et al. 2007). 

That finding is in line with many others:

- Podophilia was common in a sample of male adolescents and young adults with either autistic disorder (AD) or borderline/mild mental retardation (MR): "Partialism (a sexual interest in body parts) was common in the AD group: four individuals got sexually aroused by body parts (three by feet, one by bellies) compared to none of the MR group" (Hellemans et al. 2010). 

- A former escort girl and stripper "reported that [her] most frequent requests were (1) those involving a foot or shoe fetish, (2) those to sell to the male client her underwear, and (3) those to urinate into her underwear before selling it to the client" (Cernovsky 2015). 

- Online searches that include the term "fetish" most often co-occur with the term "foot" (Anon 2007)

- The Austrian psychologist Wilhelm Stekel noted that ''the most widespread form of partialism is preference for feet” (Stekel 1952, p.169)

Female feet have been eroticized even by Victorian writers like George du Maurier (1834-1896):

"That's my foot," she said, kicking off her big slipper and stretching out the limb. "It's the handsomest foot in all Paris. There's only one in all Paris to match it, and here it is," and she laughed heartily (like a merry peal of bells), and stuck out the other.

And in truth they were astonishingly beautiful feet, such as one only sees in pictures and statues—a true inspiration of shape and color, all made up of delicate lengths and subtly modulated curves and noble straightnesses and happy little dimpled arrangements in innocent young pink and white. (Du Maurier 1894, p. 174)

The cause?

There has been a lot of speculation. Ramachandran and Hirstein (1998) attributed podophilia to accidental cross-talk between adjacent regions of the cortex:

In the Penfield homunculus the genitals are adjacent to the foot and, as one might expect, we found that two [amputee] patients reported experiencing sensations in their phantom foot during sexual intercourse. [...] (One wonders whether foot-fetishes in normal individuals may also result from such accidental 'cross wiring'—an idea that is at least more plausible than Freud's view that such fetishes arise because of a purported resemblance between the foot and the penis.)

Actually, Sigmund Freud proposed three hypotheses. He listed them in a footnote and apparently had no strong opinions on the subject. His first hypothesis was that feet are fetishized because they are strong-smelling. His second was that “[t]he foot replaces the penis which is so much missed in the woman.” Finally, he suggested that foot fetishism arises from male desire being redirected away from the female genital area because of “prohibition and repression” (Freud 1920, n19).

The third hypothesis seems to me the most interesting. A young man may focus on a woman’s feet because he cannot look too long at other parts of her body either because of social discomfort (in the case of her face or her breasts) or because they are concealed by clothing, so he looks at a body part that is exposed and freely observable. This is especially a problem in societies where an unmarried woman is expected to cover herself when seen by a man from outside her family (i.e., neither her father nor her brothers). Only her face, hands, and feet may be seen, and sometimes not even her face. Her feet thus become a focus of male erotic interest and sexual fantasizing. With repeated reinforcement and conditioning, they may even become a primary source of sexual arousal.

The reinforcement and conditioning hypothesis has two problems: 

1). In Western societies, socks and other footwear have been worn indoors and out since the eighteenth century, and women’s arms, legs, and upper chests have become denuded since the early twentieth century. If feet no longer rank among the top three areas of naked female skin, shouldn’t podophilia be a lot less common nowadays?   

2). Although puberty seems to be key to development of podophilia, a survey of foot fetishists showed that about half of them remembered feeling attraction to feet at earlier ages:

45 per cent thought that the fetishism was linked to pleasurable experiences during childhood. Many men had their first feelings of sexual pleasure with a member of the family's feet (fathers, uncles, brothers), the experience connected to innocent activities such as tickling or washing feet [...] (Peakman 2013, p. 379)

The mental circuitry thus seems to be already in place by childhood, at an age when sexual fantasizing is still rudimentary at best.


Perhaps some of that circuitry has become hardwired, through a process of gene-culture coevolution. In societies where young unmarried women had to conceal most of their body surface from public view, foot fetishizing may have developed as a safe form of premarital eroticism. That kind of social environment rewarded “good boys” who played by the rules of premarital sexuality, while penalizing “bad boys” who didn’t. The first group would tend to have a certain mix of hardwired sexual predispositions: not only inhibition of overt sexual interest but also displacement of sexual interest into areas that are not socially penalized. Over time, and with each passing generation, those predispositions would have become prevalent in the gene pool.

That sounds weird, but we see such hardwiring in the courtship behavior of other mammals, which typically try to attract a potential mate through behavioral patterns drawn from other areas of social interaction, such as between a mother and her infants. In some cases, courtship can incorporate stress-induced behavior. Feelings of stress cause the male to preen himself, and preening thus becomes a regular and expected part of courtship, at which point there is strong selection to make it a hardwired component of the behavioral sequence (Manning 1972, pp. 112-118).

That kind of opportunism seems to characterize much of our sexual behavior. Kissing, for instance, was initially done only between a mother and her infants or as a gesture of respect between a subordinate and his superior. It then became sexualized in some societies but not in others (Frost 2015). Did podophilia follow a similar evolutionary path? Did it begin as a side effect of sexual repression and later became incorporated into love play? Like kissing, it may have developed as a safe alternative to sexual intercourse. Unlike kissing, it has not reached the same level of social acceptance. Keep in mind that even kissing is frowned upon in many societies. 

To test this hypothesis, we need cross-cultural data. Is podophilia more frequent in those societies where, at least until recent times, most of a woman’s body surface was hidden from the gaze of male strangers?


Anon. (2007). The AOL Search Data: Self Identified Fetishers. Accessed September 4, 2019

Cernovsky, Z.Z. (2015). Fetishistic Preferences of Clients as Ranked by a Sex Worker. Journal of Sex & Marital Therapy 42(6): 481-483. 

Du Maurier, G. (1894). Trilby. Harper’s New Monthly Magazine. January 88(524): 168-189.

Freud, S. (1920). Three contributions to the theory of sex. Second edition. New York: Nervous and Mental Disease Publishing Co. 

Frost, P. (2015). Not everyone does it. Evo and Proud, July 18

Hellemans, H., H. Roeyers, W. Leplae, T. Dewaele, and D. Deboutte. (2010). Sexual Behavior in Male Adolescents and Young Adults with Autism Spectrum Disorder and Borderline/Mild Mental Retardation. Sexuality and Disability 28(2): 93-104.

Manning, A. (1972). An Introduction to Animal Behaviour. 2nd edition. London: Edward Arnold.

Peakman, J. (2013). The Pleasure's All Mine. A History of Perverse Sex. London: Reaktion Books

Ramachandran, V.S. and W. Hirstein. (1998). The perception of phantom limbs. The D. O. Hebb lecture. Brain 121: 1603-1630.

Ribeyrol, C. (2015). 'The Feet of Love': Pagan Podophilia from A.C. Swinburne to Isadora Duncan. Miranda 11

Scorolli, C., S. Ghirlanda, M. Enquist, S. Zattoni, and E.A. Jannini. (2007). Relative prevalence of different fetishes. International Journal of Impotence Research 19: 432-437.

Stekel, W. (1952). Sexual aberrations: The phenomena of fetishism in relation to sex (Vol. 1) (Trans., S. Parker). New York: Liveright Publishing Corporation.