The costs of outbreeding: what do we know?

Charles Davenport, circa 1929 (Wikicommons)



To produce healthy children, you should marry a third or fourth cousin. Farther out, the genetic costs of outbreeding begin to outweigh those of inbreeding. That was what a cohort study found in examining Icelanders born between 1800 and 1964. Fertility was lower if the woman's husband was either closer in or farther out (Helgason et al. 2008).

That finding is supported by a Danish study. Using data on Danes born in 1954, the authors measured the distance between the wife's home parish and the husband's home parish. Fertility peaked at a distance of around 75 km. The relationship between fertility and marital radius was not explained by education, family income, urbanicity, or mother's age at first birth. The authors concluded that their findings were consistent with those of the Icelandic study, the cause being the same: fertility rises with decreasing relatedness up to a peak and then starts to fall. Inbreeding depression gives way to outbreeding depression (Labouriau and Amorim 2008).

How far can you marry out before the costs of outbreeding become unacceptable? One problem lies with that word. What may be perfectly acceptable to one person may not be to another.

So let me review what is known and what remains to be known. You be the judge.

A half-century ago, Ernst Mayr wrote: "Hybridization between species leads almost invariably to unbalance through deleterious combinations of genes. [...] in Drosophila even the hybridization of races may lead to destruction of well-integrated gene combinations" (Mayr 1970, p. 399). He then went on to say that it is "still uncertain" whether these findings apply to our species. In fact, "all investigations of race mixtures in man have failed to produce any evidence of decreased fitness."

It would be better to say "indisputable evidence." In fact, there is evidence from two major studies of the 1920s.


Davenport’s research in Jamaica

I will begin with a study by Charles Davenport, a Harvard zoology professor. In the early years of the twentieth century, he became concerned about human heredity and the genetic consequences of outbreeding. In 1926, with his assistant Morris Steggerda, he went to Jamaica and examined 100 black, 100 white and 100 “brown” adults of equal social status, together with 1200 children between the ages of 10 and 16. They were given anthropometric, physiological, and psychological tests. The psychological results are worth quoting in full:

Disharmonies in the mental sphere are socially more significant, perhaps, than those in the physical sphere, and such disharmonies are apparently common in the adult Browns [...]. Such disharmony and confusion apparently appear in visualization and reproduction, as in putting together the parts of the manikin. The proportion of failures of the Browns is 9.6 per cent, as opposed to 3.1 per cent in Blacks and 2.1 per cent in Whites. In copying of geometric figures 5 per cent of Browns fail completely, as compared with 3 per cent of the Blacks and 0 per cent of the Whites. In the Army Alpha Test IV (opposites and similars) 41 per cent of Browns got only 3.7 or fewer correct, while only 23 per cent of Blacks did so poorly and none of the Whites. In Test V (pied sentences) 30 per cent of the Browns got fewer than 3 out of 24 questions right, while only 26 per cent of the Blacks and 13 per cent of the Whites did. In Test VII (of analogies) 45 per cent of the Browns got less than 10 per cent of the questions correct, while only 30 per cent of the Blacks and 21 per cent of the Whites did so badly. One gains the general impression that, though on the average the Browns did not do so badly, there was among them a greater number of persons than in either Blacks or Whites who were muddled and wuzzle-headed. The Blacks may have low intelligence, but they generally can use what they have in fairly effective fashion; but among the Browns there appear to be an extra 5 per cent who seem not to be able to utilize their native endowment. There are so many variables, however, and the numbers are so small, that the results merely propose an hypothesis and do not warrant a conclusion.

The question arises: are there any traits in which, on the average, the adult Browns are superior to the Whites? We might, theoretically, expect such, yet when we have tested all of the probably genetically distinct traits between Blacks and Whites, we find only one in which the mean of the adult Browns is clearly higher than that of either parental stock.

On the other hand, if we examine the means for children of 10 to 13 or 13 to 16 years there are a few in which the brown children grade higher than either the black or the white children. [...] The fact that youthful Browns sometimes score higher than youthful Blacks or Whites suggests the conclusion that brown children develop in some mental capacities precociously; and then fall behind in development.

The relative underperformance of biracial individuals looks significant, given the sample sizes. Less clear is its magnitude and, most importantly, its cause. If we exclude the hypothesis of incompatibilities during development, there are only two other explanations:

- The “brown” individuals had suffered some kind of deprivation that the black and white individuals hadn't.

- “Brown” individuals with mental problems had been oversampled.

Neither explanation seems likely. In the Jamaica of the 1920s, biracial individuals were if anything a privileged group. They dominated the middle class. Nor is it clear why those with mental problems would be oversampled. 


Mjøen’s research in Norway and Sweden

The second study was by Jon Alfred Hansen Mjøen, a Norwegian who in 1906 founded the Vinderen Biological Laboratory, a center for international research in genetics. He likewise was concerned about the possible negative effects of outbreeding and became a proponent of eugenics. In 1934, he supported a Norwegian law for forced sterilization. He died in 1939. 

With the support of his laboratory, Mjøen did fieldwork in northern Norway and Sweden, where he observed and measured about 600 Norwegians/Swedes, about 600 Sami, and more than 300 people of first-generation mixed ancestry. Most individuals in the last group were described as having "harmonious faces, general good looks, decent stature, height, and strength, as well as a good correlation between volume of lungs and body-size, and muscular strength and body-size." However, "we found more disharmonies, both physical and mental, than in the two parent races."

The disharmonies were: "Relatively large or small ears, disproportionate extremities, unusual length of body in the F1 generation, abnormal range of variation with regard to such characteristics as lung-volume and muscular strength [...], greater prevalence of diabetes [...], loss of balance, and diminished resistance to tuberculosis" (Mjøen 1931).

Mjøen argued that disharmonies are most likely to occur when a trait is determined by large numbers of genes acting together, such as when hormones act on genes for growth and development: "It is highly probable that the frequently observed exaggerated growth of the hybrid and his disproportionately large extremities are due to a glandular disturbance of genetic origin." He also attributed the higher rate of diabetes to errors in hormonal regulation.


After

There were no subsequent studies. It would be easy to say that research ended with the widespread revulsion against Nazi Germany in 1945. Actually, the end came earlier, in the 1930s with the triumph of Boasian anthropology and behaviorist psychology. Both stressed the plasticity of the human mind and shifted the focus of research from nature to nurture, i.e., to "society" and possibilities for social change. 

Nonetheless, even within academia, important people continued to voice support for hereditarian and eugenic positions. John Maynard Keynes served as the director of the Eugenics Society of London (1937-1944) and in 1946 was still calling eugenics "the most important and significant branch of sociology" (Brignell 2010). The science fiction series Star Trek ran an episode in 1967 on eugenics ('Space Seed'). The Eugenics Review would be renamed The Journal of Biosocial Science only in 1969. Eugenic laws remained on the books and were enforced as late as the 1970s in some jurisdictions. 

All of this may seem surprising because there has been an effort to push the systematic rejection of eugenics farther and farther back in time. The Wiki entry on Charles Davenport, for instance, states that "only his ardent admirers" took his research seriously. The truth is that he was widely respected until the 1930s. His 1911 work, Heredity in Relation to Eugenics, became a college textbook (Wikipedia 2020). Mjøen was likewise well regarded:

His fame was such that he was one of three expert advisors consulted by the US Congress in the appointment of the first President of the American Eugenics Society, he gave a lecture tour of eighteen American universities in 1927, and, in a period in which The New York Times voiced anxieties about the future of the 'Nordic Type' in America, the newspaper of record invoked Mjøen repeatedly (Reinert 2015)

Even on the left, the general attitude was cautious acceptance, as seen in this 1928 report from the Eugenic Society of Leningrad:

P. I. Ljublinsky remarked that there was not much to be said for the two extreme views of this problem—the doctrine of complete indifference to the matter and the system of strict measures. Therefore what must be recognised as most advantageous is something lying between the two extremes,—a certain system of compromise, of which he himself was an adherent. The meeting gave its support to this last standpoint. It was decided that certain legislative prohibitions in this field are undoubtedly of service. (Philiptschenko 1928)

On the specific issue of outbreeding, feelings were more mixed:

After the conclusion of the discussion the meeting decided that, although the question of race crossing is very important, it is difficult to regard is as definitely solved. But in contrast to the attitude adopted in the Norwegian programme it must be stated that, so long as we have no other data available, we cannot express an opinion against the crossing of different races and nations. (Philiptschenko 1928)

There would be no more data. The Soviet Union, like the world in general, looked up to progressive thought in the West, particularly in the United States. By the 1930s, the shift toward blank slate thinking had become overwhelming among American intellectuals.


Conclusion

If we go back to the recent studies on fertility and outbreeding, we see that fertility progressively declines when outbreeding takes place beyond one's fourth cousin. A growing proportion of embryos or fetuses fail to develop beyond a certain point, apparently because of some incompatibility.

Outbreeding depression seems to be a real phenomenon, but how serious is it? Davenport examined perhaps the maximum degree of outbreeding possible, and only a minority of individuals showed a degree of dysfunction that was higher than expected. The proportion varied according to the mental test, from a low of about 5% to a high of 30%. It is likely that subsequent generations would show progressively lower proportions, with natural selection removing the least functional individuals through reduced fertility, inability to find a mate, or higher risk of illness. 

Davenport was cautious in interpreting his results, noting the difficulty in estimating the size of the adverse outbreeding effect. His self-criticism was taken up by his critics, and the current prevalent view is that his study has been thoroughly discredited, if not by methodological problems, then by Hitler.


References

Brignell, V. (2010). The eugenics movement Britain wants to forget. New Statesman. December 9 http://www.newstatesman.com/society/2010/12/british-eugenics-disabled 

Davenport, C.B. and M. Steggerda: (1928). Race Crossing in Jamaica. Washington: Carnegie Institution, Publication no. 395.
http://www.velesova-sloboda.info/archiv/pdf/davenport-race-crossing-in-jamaica.pdf

Helgason, A., S. Pálsson, D.F. Guðbjartsson, þ. Kristjánsson, K. Stefánsson. (2008). An association between the kinship and fertility of human couples. Science 319(5864): 813-816.
http://facelab.org/debruine/Teaching/EvPsych/files/Helgason_2008.pdf

Labouriau, R., and A. Amorim. (2008). Comment on "An Association Between the Kinship and Fertility of Human Couples" Science 322(5908): 1634
http://science.sciencemag.org/content/322/5908/1634.2.full

Mayr, E. (1970). Populations, Species, and Evolution. Cambridge (Mass.): Belknap Press.

Mjøen, J.A. (1931). Race-crossing and glands. Some human hybrids and their parent stocks. The Eugenics Review 23(1): 31-40.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2984998/?page=1

Philiptschenko, J.A. (1928). The Norwegian eugenic programme discussed at meetings of the eugenic society of Leningrad. The Eugenics Review 19(4): 294-298.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2984720/

Reinert, S.A. (2015). The economy of fear:  H.P. Lovecraft on eugenics, economics and the Great Depression. Horror Studies 6(2): 255-281.
https://www.academia.edu/19676748/The_Economy_of_Fear_H.P._Lovecraft_on_Eugenics_Economics_and_the_Great_Depression

Wikipedia. (2020). Charles Davenport.
https://en.wikipedia.org/wiki/Charles_Davenport

The 2020s are here

Elderly Shanghai woman practicing tai-chi (Wikipedia – Tom Thai)



Two years ago I wrote about "The Crisis of the 2020s." I argued that this decade would see a worsening confrontation between two world views:

On the one hand, the globalist consensus will continue to radicalize in the core countries of the Western world. On the other hand, a very different consensus will dominate most of central and eastern Europe, with inroads being made into France and Germany. These opposing consensuses will diverge more and more, if only because mutual antagonism will make dialogue impossible. (Frost 2017a)

This confrontation is taking place at a time when the "consensus" no longer seems to be delivering the goods. Economic growth is sluggish not only throughout the West but also in the supposed beneficiaries of globalization—China, in particular. For some, this slowdown means that the current system has failed. For others, it means that the failings of globalization can be resolved only through more globalization.

The Crisis of the 2020s is thus primarily ideological. People are split into opposing camps, and it is far from clear which one will win. While the globalist consensus is losing ground in eastern, central, and southern Europe, it still dominates the western core of the UK, France, and Germany ... as well as North America. The West has lost its manufacturing base but is still culturally dominant. That dominance, not so much in ideas as in the packaging of ideas, is critical to promoting a model of society where people are interchangeable units in a global marketplace.

The ideological crisis will nonetheless be made worse by real-world problems:


China: a shrinking work force

China’s exports will become more expensive as its work force shrinks and grows old. This shrinkage will be worse than expected because the Chinese authorities have been overestimating the country’s fertility rate for almost two decades. The current rate is not 1.6 children per women. In fact, it had already fallen to 1.4 by 2003 and is now probably one child per woman. And this is happening even though the one-child policy is no longer in effect. The fertility rate is even lower among Han Chinese and lower still in the industrialized northeast—where it is down to 0.75 (Frost 2019a; Wang 2018). 

There are already fewer Chinese workers with each passing year, and this decrease will accelerate as the smaller cohorts of the noughts and teens enter the job market. Inevitably, the price of labor will rise. This will be good for China, which needs to reorient away from exports and toward its domestic economy. Western countries, however, will have to be weaned off their dependence on cheap Chinese goods.

Can the same goods be produced elsewhere? Unlikely. None of the alternatives sources of cheap labor have the same worker quality or, just as importantly, worker quantity. In hindsight, China was a lucky find for globalization—a country where the average worker was not only inexpensive but also intelligent and disciplined.

Western consumers are already cash-strapped, with most of them living from pay check to pay check. Where will they get the money to pay for a steep increase in the price of consumer goods?


The global food crisis

The Arab Spring was triggered by a surge in food prices. That surge was no fluke. We are reaching the end of a long increase in food production, a “green revolution” made possible by large-scale monoculture, intensive plowing, and heavy use of chemical fertilizers. That increase has come at a price, particularly degradation of soil fertility. Further increases will be modest and will require a more sustainable model of agriculture, as well as more investment in automation and robotization. Unfortunately, such changes, especially the latter, are impeded by the current heavy reliance on cheap migrant labor.

Agribusiness, particularly in the U.S., has become a conservative force that will stubbornly resist change. Like the culture industry, it will push for more of the same.


The decline of high-trust societies

The evolution of social complexity is far from easy. One of the main challenges has been the creation of large societies in which economic transactions take place mostly between unrelated individuals. Such societies are impossible in most of the world because of the high level of mistrust between unrelated individuals. Each transaction has to be checked and double-checked for lying, cheating, and outright theft. Many transactions never take place because they just aren't cost-effective.

This obstacle has been overcome in northwest Europe and East Asia. In both areas, the solution is behavioral and psychological. Northwest Europeans are more individualistic, less loyal to kin, and more trusting of strangers. Because they attach less importance to kinship, they have been able to build large, functioning societies on the basis of “impersonal prosociality,” i.e., willingness to obey universal social rules, affective empathy toward nonkin, and feelings of guilt for unwitnessed rule breaking (Frost 2017b; Frost 2019b; Schulz et al. 2019). East Asians are less individualistic but just as willing to obey universal rules, which are enforced more by shame than by guilt. Empathy is also at a high level, but less differentiated between affective and cognitive empathy:

The main difference is in the relationship between self and society. Whereas a greater sense of self has helped Northwest Europeans to transcend the limitations of kinship and, thus, build larger societies, East Asians have relied on a lesser sense of self to create a web of interdependence that extends beyond close kin. (Frost 2015)

Northwest Europeans and East Asians are now in steep demographic decline. Inevitably, less wealth will be created. I say "inevitably" because those two groups produce most of the world’s wealth. When they go, most of the wealth will go too. This is not a problem we can resolve by passing laws or changing the school curriculum. To some extent, we could force people to adopt the behaviors of a high-trust society, but that would take time and will. And we don't have much of either.


A name with a nice ring to it

When I wrote that post two years ago I settled on the name "Crisis of the 2020s." It had a nice ring to it. While doing research for this post, I googled the same name ... and got over 56,000 hits. The oldest hit seems to be a 2011 article: "Global Aging and the Crisis of the 2020s." I hadn't read it previously, but it points to the same underlying problem:

The working-age population has already begun to contract in several large developed countries, including Germany and Japan. By 2030, it will be stagnant or contracting in nearly all developed countries, the only major exception being the United States. In a growing number of nations, total population will begin a gathering decline as well. Unless immigration or birthrates surge, Japan and some European nations are on track to lose nearly one-half of their total current populations by the end of the century. (Howe and Jackson 2011)

That article differs from mine in its implied advocacy of immigration as a solution. To be sure, it does mention "the lawlessness of immigrant youths in large cities [of Western Europe]," but it remains upbeat about the United States "because of its higher fertility rate and because of substantial net immigration, which America assimilates better than most other developed countries" (Howe and Jackson 2011). That optimism was already exaggerated in 2011. Today, mass immigration is just as much a process of cultural and demographic replacement in the U.S. as it is in Western Europe.

Let's be frank. The high productivity of North America, Western Europe, and East Asia has profound behavioral and psychological causes. It is not due to political ideals, universal education, or a particular legal system. It is due to a higher level of social trust, as well as a higher level of cognitive ability and a lower level of personal violence. When immigrants enter that kind of environment, their productivity dramatically rises. They are now working in a society where laws are observed, where information is reliable, and where disputes are not normally settled through violence. We all benefit from that kind of society—simply by virtue of living in it.

That’s the "unearned privilege" that antiracists and right-wing economists love to denounce. Their argument is deceptively simple: “By what right do we deny this privilege to others?  It’s a mere accident of birth! Just think, they’re less productive because we’re keeping them out. So let them in! We’ll all be better off!”

Well, no. Do I have to explain why? 


References

Frost, P. (2015). Two Paths. The Unz Review, January 24
https://www.unz.com/pfrost/two-paths/

Frost, P. (2017a). The Crisis of the 2020s. Evo and Proud, December 19.
http://evoandproud.blogspot.com/2017/12/the-crisis-of-2020s.html

Frost, P. (2017b). The Hajnal line and gene-culture coevolution in northwest Europe. Advances in Anthropology 7: 154-174.
https://file.scirp.org/pdf/AA_2017082915090955.pdf 

Frost, P. (2019a). Autumn in China. Evo and Proud, March 26
http://evoandproud.blogspot.com/2019/03/autumn-in-china.html 

Frost, P. (2019b). Was Western Christianity a cause or an effect? Comment on: J.F. Schulz, D. Bahrami-Rad, J.P. Beauchamp, and J. Henrich. The Church, intensive kinship, and global psychological variation. Science 366 (6466)
https://science.sciencemag.org/content/366/6466/eaau5141/tab-e-letters  

Howe, N., and R. Jackson. (2011). Global aging and the Crisis of the 2020s. Current History, January, pp. 20-25
https://pdfs.semanticscholar.org/9879/fe3ea41e85f5fdfb6bc1ffcc2ae5c44a1a2a.pdf 

Schulz, J.F., D. Bahrami-Rad, J.P. Beauchamp, and J. Henrich. (2019). The Church, intensive kinship, and global psychological variation. Science 366(707): 1-12. 
https://web.ics.purdue.edu/~drkelly/SchulzHenrichetalTheChurchIntensiveKinshipGlobaPsychologicalVariation2019.pdf

Wang, M. (2018). For Whom the Bell Tolls: A Retrospective and Predictive Study of Fertility Rates in China (November 8, 2018). Available at SSRN: https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3234861  

Not what you think

Preparing for a test (Wikicommons - Excelz)



Why do West African immigrants outperform native-born whites in UK schools? This is the question posed by Chanda Chisala using data from the GCSE, the General Certificate of Secondary Education. 

To be sure, the GCSE is not the same as an IQ test. For most subjects it includes things like coursework and attendance. The test-taker is also motivated by self-interest: a high GCSE score can be a ticket to a good university and a good job. Nonetheless, Thompson (2013) has argued that the GCSE has a correlation of 0.81 with IQ. So perhaps the two are roughly equivalent.

Let's look at the GCSE results from England for 2012. They are indeed astounding for immigrant children from English-speaking Africa. Just look at the percentage difference from the mean by country of origin:

Nigerians -     +21.8
Ghanaians -     +5.5
Sierra Leone - +1.4

Source: Chisala (2019)

This academic excellence seems to be unusually concentrated among Nigerian immigrants. Are we looking at our friends from the Niger delta? Often known as the "Jews of West Africa," the Igbo have a long record of academic and economic success. This has been attributed to their openness to Western learning and the commercial opportunities it creates, although the Igbo were, in fact, a trading nation long before the colonial era (Frost 2015). They became receptive to Western learning because they had long been receptive to learning in general, much like the Japanese during the Meiji era.

Chisala (2015) provides an ethnic breakdown of GCSE results for the years 2009 to 2011:

2009: Igbo - 100%, Yoruba - 39%
2010: Igbo - 80%, Yoruba - 68%
2011: Igbo - 76%, Yoruba - 75%

The Igbo started off as top achievers, but their lead evaporated over the next two years as the Yoruba made remarkable gains. There were 90 Yoruba kids, so sampling error could hardly explain their increase from 39% to 75%. Because the Igbo kids numbered only 16, the decrease from 100% to 76% might not be significant.

Perhaps the Yoruba kids got better coaching and tutoring. Whatever the explanation, GCSE cannot be used as a proxy for IQ, at least not for Nigerians. Yes, IQ can change over the course of a lifespan, but not that fast and not that much—unless you suffer a serious accident.


Exam malpractice

There are less innocent explanations for the rapid rise in Yoruba scores. A study of students in Nigeria found that test-retest reliability ranged from 77 to 85% (Petters and Okon 2014). The authors blame the low test reliability on cheating, calling it "a plague":

Examination malpractice in Nigeria has attained a frightening proportion and it is becoming more sophisticated as years pass by. Efforts by government and stakeholders to curtail this trend have not yielded much success. If this trend is not given an urgent attention, it may utterly destroy the quality of education in Nigeria.

Bisong et al. (2009) come to similar conclusions:

The implication of this study is that the cheating tendency is becoming endemic in Nigerian society. A situation where one in every four students tends to cheat in every examination calls for a significant moral questioning of our society. Even with a high level of supervision, as the results show, students are still prone to indulge in cheating behaviour.

In their review of the literature, Bisong et al. (2009) note that "in 1980, out of the 190,000 candidates who sat the West African Examination Certificate in May and June, 46,000 candidates from Nigeria had their results nullified." Cheating is partly due to Nigerian parents, who understand the value of academic success and push their children to get good grades "by all means":

Parents expect nothing less than passing in examination from their children. There must not be failure. That is to say that he who fails is not entertained in any way. Where there is weakness or a psychological measure that one is not prepared to pass the examination, then fear begins to disturb the minds of students as to how to make it. This leads to serious reading throughout the night, pressing lectures for areas of concentration and arranging to enter the examination hall with every possible means to cheat during the examination. (Halima 2003, p. 17)

Halima (2003, p. 19) notes the harshness of penalties for cheating: "in 1983 the punishment for cheating was increased to a jail term of 21 years without the option for fine. In spite of this cheating in examination increased."


Nigeria's cognitive elite?

It has been argued, notably by Greg Cochran, that Nigerian immigrants are skimmed from the top of their country's IQ distribution (Cochran 2019). They are the best that Nigeria has to offer—la crème de la crème. To make that argument work, however, Nigerian immigrants to the UK would have to be much smarter than the average Nigerian, with an IQ more than one standard deviation higher and probably two.

There is only a rough consensus on the mean IQ of sub-Saharan Africa. In their review of the literature, Wicherts et al. (2010) argue for a mean of 82, whereas Lynn (2010) puts it at 66. Rindermann (2013) favors a "best guess" of 75. Even if we take the high estimate of 82, we must still assume extreme selection to get a mean IQ above 100. Is that a reasonable assumption?  Elite individuals exist among immigrants from Nigeria, but they are not the majority: 

Socially, the Nigerian diaspora is by no means homogenous. There are those who struggle for basic means of survival such as car park attendants, cleaners and other menial workers working long hours to make ends meet. But some professionals have distinguished themselves and moved on to become members of the Black middle class. (Akinrinade and Ogen 2011)

Furthermore, some doubt may be cast on the credentials of middle-class Nigerians: "they have acquired a notorious reputation for arrogance and fraud" (Akinrinade and Ogen 2011). Finally, the cognitive elite argument fails to explain why immigrants from Nigeria do so much better than those from Ghana and Sierra Leone.


Math scores

On many GCSE components, there is much room for cheating, particularly on coursework. But what about the mathematics component? GCSE math has not had coursework since 2009. It is simply a timed test. How can one cheat on a timed test?

By impersonation. A "ghost" who knows the subject takes the exam by impersonating the student, and the actual student never takes the exam (Azuka 2014). This method requires a photo ID that combines the ghost's photo with the test-taker's name. In most cases, the fake ID is sufficient to dispel any suspicions.


Conclusion

For whatever reason, the GCSE is too volatile to be used as a proxy for IQ, particularly in the case of Nigerian students. The volatility seems to be due to cheating, as well as to the grey area of coaching and tutoring services. Cheating is rife among Nigerians in Nigeria, and it would be naïve to suppose that such behavior disappears once they relocate to another country, especially if their new country imposes none of the harsh penalties that are regularly imposed in Nigeria.

Nigerian academic achievement may be genuine in some cases. This is particularly so with respect to the Igbo, who have a longstanding record of achievement within and outside school. Unfortunately, genuine ability can be cofounded with fake ability. Smart people are better at gaming the system and making themselves look smarter than they really are.

Indeed, I can't help wondering when I look at the GCSE results for Igbo students in 2009. Every single Igbo got a perfect score—that's unusual even for a smart population and even with a sample size that small. Chanda suggests that year-to-year fluctuations might have made the sample even smaller in that year. Well, perhaps.

It would be easy to say that we need more data. Additional GCSE results, however, will be just as distorted by academic fraud. We need data from real IQ tests that provide no incentive for cheating.


References

Akinrinade, S., and O. Ogen. (2011). Historicising the Nigerian Diaspora: Nigerian Migrants and Homeland Relations. Turkish Journal of Politics 2(2): 71-85.
https://s3.amazonaws.com/academia.edu.documents/31034426/tjp_sayi_4.pdf?response-content-disposition=inline%3B%20filename%3DTurkish_Journal_of_Politics_TJP_V._2_N..pdf&X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=AKIAIWOWYYGZ2Y53UL3A%2F20191221%2Fus-east-1%2Fs3%2Faws4_request&X-Amz-Date=20191221T170342Z&X-Amz-Expires=3600&X-Amz-SignedHeaders=host&X-Amz-Signature=033191eb3309b04839db9b399a1976750b779991740778b6044b92573f0b1501#page=73

Azuka, E.B. (2014). Academic Fraud among Students in Higher Education in Nigeria: Reasons, Methods Adopted and Strategies to curb it. Journal of Educational and Social Research 4(3): 289-296.
https://www.mcser.org/journal/index.php/jesr/article/view/2725 

Bisong, N.N., F. Akpama, and P.B. Edet. (2009). Cheating Tendency in Examinations among Secondary School Students in Nigeria:  a case study of schools in the Odukpani Local Government Area, Cross River State. Policy Futures in Education 7(4): 410-415
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.1030.3426&rep=rep1&type=pdf  
Chisala, C. (2019). Why Do Blacks Outperform Whites in UK Schools? The Unz Review, November 29
https://www.unz.com/article/reply-to-lance-welton-why-do-blacks-outperform-whites-in-uk-schools/?showcomments#comments 

Chisala, C. (2015). UK: Igbo Nigeria Academic performance destroys the myth of Black Low IQ. Afripol November 28
http://afripol.org/afripol/item/1813-uk-nigerian-academic-performance-in-destroys-the-myth-of-black-low-iq.html

Cochran, G. (2019). Selective immigration. West Hunter, March 13
https://westhunt.wordpress.com/2019/03/13/selective-immigration/

Frost, P. (2015). The Jews of West Africa? The Unz Review, July 4
https://www.unz.com/pfrost/the-jews-of-west-africa/ 

Halima, D. (2003). A study of some socio-psychological factors of cheating in examination among students of Kaduna Polytechnic. Post Graduate School Ahmadu Bello University Zaria.
http://kubanni.abu.edu.ng/jspui/bitstream/123456789/2190/1/A%20%20STUDY%20OF%20SOME%20SOCIO-PSYCHOLOGICAL%20FACTORS%20OF%20CHEATING%20IN%20EXAMINATION%20AMONY%20STUDENTS%20OF%20%20KADUNA%20POLYTECHNIC.pdf 

Lynn, R. (2010). The average IQ of sub-Saharan Africans assessed by the Progressive Matrices: A reply to Wicherts, Dolan, Carlson & van der Maas. Learning and Individual Differences 20(3): 152-154.
https://www.sciencedirect.com/science/article/pii/S1041608010000348

Petters, J.S., and M.O. Okon. (2014). Students' Perception of Causes and Effects of Examination Malpractice in the Nigerian Educational System: The Way Forward for Quality Education. Procedia - Social and Behavioral Sciences 114: 125-129
https://www.sciencedirect.com/science/article/pii/S187704281305310X

Rindermann, H. (2013). African cognitive ability: Research, results, divergences and recommendations. Personality and Individual Differences 55: 229-233.
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.372.5462&rep=rep1&type=pdf

Thompson, J. (2013). IQ and GCSE Results in England R=0.81. The Unz Review, November 5
https://www.unz.com/jthompson/iq-and-gcse-results-in-england-r081/ 

Wicherts, J.M., C.V. Dolan, and H.L.J. van der Maas. (2010). A systematic literature review of the average IQ of sub-Saharan Africans. Intelligence 38: 1-20.
http://www.iapsych.com/iqmr/fe/LinkedDocuments/wicherts2010b.pdf

Weird people

Weird people. Northwest Europeans are more individualistic, less loyal to kin, and more trusting of strangers. (Wikicommons)



Northwest Europeans are WEIRD ... as in Western, Educated, Industrialized, Rich, and Democratic. These traits are in turn associated with certain behavioral and psychological characteristics: "People from these societies tend to be more individualistic, independent, and impersonally prosocial (e.g., trusting of strangers) while revealing less conformity and in-group loyalty" (Schulz et al. 2019).

In a recent study, Schulz et al. (2019) argue that WEIRDness is a heritage of Western Christianity: the branch of the Christian faith that gradually evolved into Roman Catholicism and, later, Protestantism: "we propose that the Western Church's transformation of European kinship, by promoting small, nuclear households, weak family ties, and residential mobility, fostered greater individualism, less conformity, and more impersonal prosociality."

Social relations are indeed different north and west of a line running approximately from Trieste to St. Petersburg, Everyone is single for at least part of adulthood, and many stay single their entire lives. In addition, households often have non-kin members, and children usually leave the nuclear family to form new households (Hajnal, 1965; ICA, 2013; Laslett, 1977). This is the Western European Marriage Pattern (WEMP), and there is an extensive literature on it going back to work by John Hajnal.


Was the Western Church a cause or an effect?

Schulz et al. (2019) stress the role of the Western Church in creating the WEMP, particularly by banning consanguineous marriages. The ban came about because "the Church had become obsessed with incest."

That isn't the whole story. Even before Christianity, Roman Civil Law forbade marriages within four degrees of consanguinity. The number was increased from four to seven in 732 by Pope Gregory III, but in this he was following similar bans among the newly converted Germanic peoples. The mid-seventh century Visigothic Code proclaimed that "it shall not be lawful to defile the blood of such as are related even to the sixth degree, either by marriage or otherwise" (McCann 2010, p. 57). In the early ninth century, the Church changed its way of calculating degrees of kinship by adopting the Germanic system. Under the old Roman system, first cousins were considered fourth degree; the Germanic system made them second degree. This change had the effect of doubling the number of ineligible marriage partners (McCann 2010, pp. 57-58).

Schulz et al. (2019, p. 2) assume that the WEMP postdates these prohibitions against cousin marriage: "by 1500 CE (and centuries earlier in some regions), much of Europe was characterized by a virtually unique configuration of weak (nonintensive) kinship marked by monogamous nuclear households, bilateral descent, late marriage, and neolocal residence." 

Actually, no one really knows when this pattern arose. As we go farther back in time, we have less demographic data to work with, but the same pattern still appears in the little we do have. In thirteenth-century Lincolnshire before the Black Death, households were already nuclear and a late age of first marriage was the norm, being 24 for the woman and 32 for the man (Hallam 1985, p. 66). In ninth-century France, two surveys show that households were small and nuclear among married people and that 12 to 16% of the adult population were unmarried (Hallam 1985, p. 56). A third survey shows that both men and women were marrying in their mid to late twenties; (Seccombe 1992, p. 94). Admittedly, the earliest data are limited to France, hence the authors' caveat "centuries earlier in some regions," but France was hardly an outlier in the demographic evolution of northwest Europe.

Earlier demographic data are too fragmentary to produce firm conclusions. Furthermore, the data usually concern elite males who typically took much younger brides. Nonetheless, in the general population we see some evidence of first marriages at late ages. The first-century Roman historian Tacitus wrote about the Germanic tribes: "Late comes love to the young men, and their first manhood is not enfeebled; nor for the girls is there any hot-house forcing; they pass their youth in the same way as the boys" (Tacitus Germania 20). Julius Caesar made the same observation: 

Those who have remained chaste for the longest time, receive the greatest commendation among their people: they think that by this the growth is promoted, by this the physical powers are increased and the sinews are strengthened. And to have had knowledge of a woman before the twentieth year they reckon among the most disgraceful acts; of which matter there is no concealment, because they bathe promiscuously in the rivers and [only] use skins or small cloaks of deers' hides, a large portion of the body being in consequence naked. (Caesar De Bello Gallico 6: 21)

The direction of causality may thus run in the other direction. The WEMP does not exist because the Western Church diverged from the Eastern Church on the issue of consanguineous marriage. Rather, this divergence arose because the Western Church was assimilating the behavioral norms of its newly converted peoples, including the WEMP. By the eighth century, those peoples were dominant within the Western Church and able to push Christian practice in certain directions, particularly postponement of marriage and marriage outside the kin group (Frost 2017). The tail began to wag the dog.


Sources of inspiration?

Schulz et al. (2019) seem to have been inspired by earlier work by Steven Heine and Joseph Henrich (who is one of the co-authors). Curiously, no references are made to the literature on the WEMP, not even to the work by John Hajnal. Less curiously, they pass over the more speculative work by myself, hbd chick, and Kevin MacDonald (Frost 2011; Frost 2017; hbd chick 2011; hbd chick 2012; hbd chick 2014; MacDonald 1990; MacDonald 2011). To the best of my knowledge, Kevin was the first to notice an apparent relationship between northwest Europeans, Western Christianity, and certain psychological and behavioral characteristics. This is evident in his 1990 article and even more so in his 2011 one:

The nuclear family, freed from extended kinship obligations, is the basis of Western social organization. It is unique relative to other culture areas. This pattern is particularly noticeable in the Northwest of Europe rather than the Pontic steppe region. As one goes from the Northwest of Europe to the Southeast, there is an increase in joint family structure, with brothers living together with parents, grandparents and children. Family historian John Hajnal discovered the "Hajnal line" that separates Western Europe from Eastern Europe, the former characterized by nuclear family structure, relatively late marriage and large numbers of unmarried in economically difficult times, the latter by joint family structure and relatively early and universal marriage.

I suspect Schulz et al. (2019) had read material by all three of us. I base my suspicion partly on their use of certain terms and expressions and partly on their references, particularly the curious reference to Claude Lévi-Strauss as an authority on kinship. An American anthropologist would normally cite Lewis Henry Morgan or Robin Fox. I like to cite Lévi-Strauss partly because I was trained at a French-language university and partly because he was, in a sense, my academic grandfather, being the dissertation supervisor of my dissertation supervisor.  He was also the first to come up with the concept of gene-culture coevolution, but that fact is poorly known even among francophone anthropologists.

Anyway, does it matter? The important thing is to put new ideas into circulation.


References

Frost, P. (2017). The Hajnal line and gene-culture coevolution in northwest Europe. Advances in Anthropology 7: 154-174.
http://file.scirp.org/pdf/AA_2017082915090955.pdf 

Frost, P. (2011). The Western European Marriage Pattern. Evo and Proud. November 12 http://evoandproud.blogspot.ca/2011/11/western-european-marriage-pattern.html 

Hajnal, J. (1965). European marriage patterns in perspective: essays in historical demography. In D.V. Glass and D.E. Eversley (eds). Population in History. Chicago: Aldine Publishing, pp. 101-143.

Hallam, H.E. (1985). Age at first marriage and age at death in the Lincolnshire Fenland, 1252-1478. Population Studies 39(1): 55-69.

hbd chick (2014). Big summary post on the Hajnal Line. October 3
https://hbdchick.wordpress.com/2014/03/10/big-summary-post-on-the-hajnal-line/

hbd chick (2012). Behind the Hajnal Line. January 16
https://hbdchick.wordpress.com/2012/01/16/behind-the-hajnal-line/  

hbd chick (2011). The Hajnal Line. June 30
https://hbdchick.wordpress.com/2011/06/30/the-hajnal-line/  

ICA (2013). Research Themes - Marriage Patterns, Institutions for Collective Action http://www.collective-action.info/_THE_MarriagePatterns_EMP

Laslett, P. (1977). Characteristics of the Western family considered over time. Journal of Family History 2(2): 89-115.

MacDonald, K. (2011). Going against the Tide: Ricardo Duchesne's Intellectual Defence of the West. The Occidental Quarterly 11(3): 1-22.
http://www.kevinmacdonald.net/duchesne-review.pdf 

MacDonald, K. (1990). Mechanisms of sexual egalitarianism in Western Europe. Ethology and Sociobiology 11: 195-238.
http://www.kevinmacdonald.net/E&S1990.pdf

McCann, C.A. (2010). Transgressing the Boundaries of Holiness: Sexual Deviance in the Early Medieval Penitential Handbooks of Ireland, England and France 500-1000. Theses. 76.  Seton Hall University https://scholarship.shu.edu/theses/76 

Schulz, J.F., D. Bahrami-Rad, J.P. Beauchamp, and J. Henrich. (2019). The Church, intensive kinship, and global psychological variation. Science 366(707): 1-12. 
https://web.ics.purdue.edu/~drkelly/SchulzHenrichetalTheChurchIntensiveKinshipGlobaPsychologicalVariation2019.pdf

Seccombe, W. (1992). A Millennium of Family Change. Feudalism to Capitalism in Northwestern Europe. London: Verso.

Candida and autism

Shamanic ritual (Wikipedia - Idries Shah). There is a correlation between autism and antibodies for Candida albicans. Does a pathogenic strain of this yeast promote the development of autism? Cui bono?


In my previous posts I've argued that certain pathogens have acquired the capacity to manipulate human behavior. Humans are an interesting target for several reasons:

1. The human mind oversees an extensive range of complex behaviors

2. Humans are long-lived, thus providing a useful vehicle for spreading to other potential hosts.

3. Humans have particularly long generation times and are thus less able to develop resistance to short-generation pathogens, which can more easily “outmanoeuvre” the evolution of human resistance.

Among animal hosts in general, behavior can be manipulated by many pathogens, including fungi. Fungi seem to be better able than viruses and bacteria at producing and coordinating the array of chemicals needed for the targeted neural tissue. One of them may be Candida, a genus of yeasts that most often live in the gut but can be found elsewhere in the body. In particular, there seems to be a connection between their presence and the development of autism spectrum disorders (ASD):

We aimed to determine if children with ASD exhibit elevations in antibodies that target C. albicans, indicating current or previous overgrowth of this fungal species. [...] Plasma anti-C. albicans antibody positivity was found in 36.5% (19/52) of children with ASD. Anti-C. albicans antibodies in typically developing controls was (14.3%; 4/28). Overall, ASD children had a higher rate of high-positive values compared to typically developed children with an unadjusted odds ratio of 3.45 (95% confidence interval, 1.0409 to 11.4650; p = 0.041, two-tailed). (Hughes and Ashwood 2018)

The above study takes the line that Candida albicans is a "passive commensal" that "under certain conditions [...] is capable of transitioning to its pathogenic and invasive fungal form" (Hughes and Ashwood 2018). In reality, C. albicans encompasses a variety of strains, some of which live more as a commensal and others more as a pathogen: 

Here, intra-species analyses of C. albicans isolates revealed extensive variation between strains, both at the genotypic and phenotypic level. Substantial genomic differences were observed between the set of 21 clinical strains and included single nucleotide polymorphisms, inversions, copy number changes, LOH events, and whole or partial chromosomal aneuploidies.

[...] The phenotypic plasticity of this species has long been recognized, and our studies reveal the genetic differences underlying phenotypic differences are due to a variety of mechanisms, of which LOH and aneuploidy are major contributors. Furthermore, we uncover a genetic polymorphism responsible for altered phenotypic behavior, including a change in the balance between commensalism and pathogenesis. (Hirakawa et al. 2015)

Some strains of C. albicans have evolved the capacity to adhere to neural tissue:

An ex vivo adhesion assay was used to examine adhesion of Candida albicans yeast cells to brain tissue of the primate Macaca mulata. Tissues from frontal lobes and striatum (caudate, putamen, and portions of the globus pallidus) were used in the assay. Yeast cells adhered to gray matter at about six times the level of adhesion to white matter. The fungus was able to bind to different cell types within the cortex, basal ganglia, and white matter. Binding to neurons, small neurons or glia, endothelial cells, and neuropil was observed. (Denaro et al. 1995)

What's in it for the pathogen?

This is the weakest link in the argument for behavioral manipulation. How does autism benefit the pathogen? Does it help Candida spread to another host? If not, where is the benefit? People have speculated about the evolutionary advantage of autism, but only from the standpoint of the affected person. Perhaps a low dose makes one more inventive and creative (Pickard et al. 2011). Perhaps it gives rise to the "autonomous imagination" of shamans:

[…] “autonomous imagination” [is] a framework for cross-cultural interpretations of inner experience such as dreams, waking visions, trance, spirit possession and mediumship, and shamanistic and meditative states.

[…] Autonomous imagination is characterized by: a) being more freely and richly inventive than ordinary thought; b) emerging into conscious awareness in the form of vivid hallucinatory imagery which is experienced as an external reality; c) possessing a more extensive access to memory; d) exhibiting a special sensitivity to external cues and direction which enables communication to and from deeper levels of the mind, while bypassing conscious awareness, and; e) possessing a capacity to influence somatic and intrapsychic processes usually beyond conscious control (Stephen and Suryani 2000)

Shamans, through their prestige and reproductive success, may have favored a predisposition to autism in the gene pool. This hypothesis assumes that autism is mainly due to a genetic predisposition, i.e., that autism is highly heritable. In fact, heritability is "moderate": 37% for autism and 38% for autism spectrum disorder (Hallmayer et al. 2011). As with male homosexuality, it looks like something in the environment is interacting with a genetic predisposition.

If we take the pathogen's standpoint, we must ask how an autistic person might become an interesting means to spread from one host to another. One possibility is the shaman's role as a community healer. Certain healing practices involve intimate contact. In particular, a shaman's phlegm may be thought to contain the essence of his power. 

A shaman also has a magical phlegm called yachay, lodged in his stomach, which gives him the ability to blow away evil and to such out the sorcery objects (virote) that cause certain forms of illness. (Gow 1996, p. 93)

By targeting people who are likely to fill the position of community healer, a pathogen could greatly increase its opportunities for transmission. 


Parting thought

This example suggests that the evolution of behavioral manipulation can involve more than a pathogen and a host. It may also require a genetic predisposition and a cultural context that create opportunities for behavioral manipulation.


References

Denaro, F.J., J.L. Lopez-Ribot, and W.L. Chaffin. (1995). Adhesion of Candida albicans to brain tissue of Macaca mulata in an ex vivo assay. Infection and Immunity 63(9): 3438-3441.
https://iai.asm.org/content/iai/63/9/3438.full.pdf

Gow, P. (1996). River People: Shamanism and History in Western Amazonia. In Thomas, N., and C. Humphrey (eds). Shamanism, History, and the State (pp. 90-113). Ann Arbor: The University of Michigan Press. 
https://books.google.ca/books?hl=fr&lr=&id=3_inrj3puRQC&oi=fnd&pg=PA90&dq=%22River+People:+Shamanism+and+History+in+Western+Amazonia%22&ots=r2_OIZbV5M&sig=aH8LVaJwqbmFUn3FpuARh3N3UF8#v=onepage&q=%22River%20People%3A%20Shamanism%20and%20History%20in%20Western%20Amazonia%22&f=false

Hallmayer, J., S. Cleveland, A. Torres, et al. (2011). Genetic Heritability and Shared Environmental Factors Among Twin Pairs With Autism. Archives of General Psychiatry 68(11): 1095-1102.
http://www.feat.org/Portals/0/Document%20Library/Medical%20Research%20Abstracts/GeneticHeritability_2011_07_04.pdf 

Hirakawa, M.P., D.A. Martinez, S. Sakthikurmar, M.Z. Anderson, A. Berlin, S. Gujja; et al. (2015). Genetic and phenotypic intra-species variation in Candida albicans. Genome Research 25: 413-425.
https://europepmc.org/articles/pmc4352881

Hughes, H.K., and P. Ashwood. (2018). Anti-Candida albicans IgG antibodies in children with autism spectrum disorders. Psychiatry 26 November
https://www.frontiersin.org/articles/10.3389/fpsyt.2018.00627/full

Pickard, C., B. Pickard, and C. Bonsall. (2011). Autistic spectrum disorder in prehistory. Cambridge Archaeological Journal 21(3): 357-364.
https://www.research.ed.ac.uk/portal/files/539348/2011_CAJ_Pickard_etal.pdf

Stephen, M. and L.K. Suryani. (2000). Shamanism, psychosis and autonomous imagination. Culture, Medicine and Psychiatry 24: 5-40.
https://link.springer.com/article/10.1023/A:1005528028869

Behavioral manipulation: population differences in virulence

Helicobacter pylori (Wikicommons – NIH). Some human populations have become resistant to this bacterium; others have not. Could the same be true for pathogens that manipulate human behavior?



Humans are behavioral creatures par excellence. Our brains oversee a large repertoire of behaviors, each of which is vulnerable to manipulation. We can be manipulated by psychological means, like the parasite who lives off the altruism of others.  There's also ideological manipulation. 

And then there's hardwired manipulation—an organism enters your mind and rewires some of its circuitry. That kind of manipulation is poorly known. We know a lot about short-term infections that make you sick. We know much less about long-term infections where the pathogen hangs around in your body without triggering an immune response. There’s no fever, no rash, no abscess. Yet it may be doing something to the most important organ of your body, perhaps to increase its chances of spreading to another host. Not surprisingly, the adverse effects become worse when you're no longer of much help. It no longer has anything to lose from trashing its host.

So if a pathogen is screwing with your mind, the symptoms will be especially severe in two cases: 

- You’re approaching the end of your life. The pathogen has less incentive to keep you healthy. You’re also less active socially and sexually, and thus less useful as a vehicle for transmission to other hosts.

- The pathogen is spreading out of its original host population and into new hosts that have not had time to develop resistance to its worse effects

This post is about the second case. You pay a cost when a pathogen monkeys around with your mental circuitry. Over time, there will be selection for humans who better resist such manipulation. Eventually, an equilibrium is reached: the pathogen still screws around with your mind, but the negative consequences are kept to a minimum. In most cases. And until it spreads to people who have no resistance.

The latter situation has been covered by a recent review article:

[...] the effects of susceptibility and virulence alleles in the respective gene pools of humans and pathogens are often contingent upon each other. The evolution of virulence is a dynamic process, easily perturbed by extrinsic variables over space and time, and therefore unlikely to follow the same trajectory in every population. [...] Whether the result is a steady-state equilibrium due to a perpetual "arms race" or a commensal detente, the same genes and pathways are unlikely to be involved in every population. As a consequence, when humans and pathogens migrate to new environments or admix, the ensuing disruption of co-evolutionary equilibria and loss of complementarity between host and pathogen genotypes may yield unpredictable and potentially deleterious biomedical consequences. (Kodaman et al. 2014)

The authors cite the example of Helicobacter pylori, a bacterium that lives in the stomach lining. It is a risk factor for gastric cancer, but the level of risk varies according to the population it infects:

Studies of human or H. pylori genetics in isolation have generally failed to explain why populations with similar rates of H. pylori infection exhibit strikingly different susceptibilities to gastric cancer. For example, in many African and South Asian countries, the low incidences of gastric cancer in the presence of almost universal rates of H. pylori infection remain a source of much speculation, and have been referred to collectively as the "African enigma" and the "Asian enigma" [...] In Latin America, where H. pylori strains native to Amerindian populations have been largely displaced by European strains [...], the predominantly Amerindian populations living at high altitudes suffer disproportionately from gastric cancer relative to other populations with similar infection rates [...]. These and other points of evidence raise the possibility that the pathogenicity of a given H. pylori strain may vary with human genomic variation, and that some individuals may be better adapted to their infecting strains than others. (Kodaman et al. 2014)

Manipulating sexual behavior

Pathogens thus differ in their virulence from one human population to another. The same should be true for those pathogens that manipulate human behavior to improve their chances of spreading from one human to another. For them, our most interesting behavior is sex, and the most interesting human populations are "leaky" polygynous ones with high rates of infidelity. In that kind of context they can spread rapidly from one household to another.

Polygyny rates are highest among the tropical farming peoples of sub-Saharan Africa (Dalton and Leung 2011; Pebley and Mbugua 1989). Traditionally, 20 to 40% of all marriages are polygynous, and most women live in polygynous households. Not surprisingly, many men, particularly young men, are single. Their opportunities for sex are limited to rape, affairs with the wives of other men, or abduction of women during times of war:

Typically, the more men are polygynous in a given society, the greater the age difference between husbands and wives. [...] The temporary celibacy of young men in polygynous societies is rarely absolute, however. While it often postpones the establishment of a stable pair-bond and the procreation of children, it often does not preclude dalliance with unmarried girls, adultery with younger wives of older men, or the rape or seduction of women conquered in warfare. Thus, what sometimes looks like temporary celibacy is, in fact, temporary promiscuity. (van den Berghe 1979, pp. 50-51)

Cuckold envy: a case of behavioral manipulation?

This is the environment in which a sexually transmitted pathogen can leapfrog from one polygynous household to another. The main obstacle is male jealousy and male "guarding behavior." The pathogen can increase its chances of transmission by disabling mate guarding or, better yet, reversing it. This kind of host manipulation has been shown in a non-human species: male isopods no longer guard their mates when they get infected by a certain parasite (Mormann, 2010).

In a human context, a pathogen may reverse male jealousy and make its host want to be cuckolded, as a means to gain access to more hosts (Frost 2013). Many sexual fetishes are mentioned in ancient writings: pedophilia, cunnilingus, fellatio, and bestiality, but not cuckold envy. The oldest mentions go back to seventeenth-century England (Kuchar, 2011, pp. 18-19).

Perhaps a sexually transmitted pathogen came to England from West Africa during the early days of the slave trade. Such a pathogen would have evolved in a context where most women were in polygynous marriages and where cuckoldry was the main route for invading one set of wives after another. Meanwhile, the human hosts may have evolved some kind of resistance, perhaps through “overwiring.” Or perhaps a certain level of cuckoldry became socially accepted. No such resistance, however, had evolved in England or elsewhere in the Western world.

As time goes on, we will discover that many STDs have evolved a capacity for behavioral manipulation, specifically by making the host either more promiscuous or less jealous.


References

Dalton, J.T., and T.C. Leung. (2011). Why is Polygyny More Prevalent in Western Africa?
An African Slave Trade Perspective,
http://www.wfu.edu/~daltonjt/PolygynySlaveTrade.pdf

Frost, P. (2013). First, sexual transmissibility and then …? Evo and Proud, January 5
http://evoandproud.blogspot.com/2013/01/first-sexual-transmissibility-and-then.html 

Kodaman, N., R.S. Sobota, R. Mera, B.G. Schneider, and S.M. Williams. (2014). Disrupted human-pathogen co-evolution: a model for disease. Frontiers in Genetics 25 August
https://www.frontiersin.org/articles/10.3389/fgene.2014.00290/full

Kuchar, G. (2001). Rhetoric, Anxiety, and the Pleasures of Cuckoldry in the Drama of Ben Jonson and Thomas Middleton. Journal of Narrative Theory 31(1): 1-30.

Mormann, K. (2010). Factors influencing parasite-related suppression of mating behavior in the isopod Caecidotea intermedius, Theses and Dissertations, paper 48
http://via.library.depaul.edu/etd/48  

Pebley, A. R., and W. Mbugua. (1989). Polygyny and Fertility in Sub-Saharan Africa. In R. J. Lesthaeghe (ed.), Reproduction and Social Organization in Sub-Saharan Africa, Berkeley: University of California Press, pp. 338-364.

van den Berghe, P.L. (1979). Human Family Systems. An Evolutionary View. New York: Elsevier.