Saturday, December 31, 2016

Population Differences in Androgens Fail to Support Differential-K Theory

According to a controversial theory, Differential-K, major human populations differ in a systematic way along a continuum of psychological and physical characteristics, based on their preferred reproductive strategies. These presumed characteristics include intelligence, personality, sexual behavior and attitudes, and even, according to Richard Lynn, penis length. (I discuss this last topic in detail here.)

Discussion of racial differences can become heated, but hopefully cooler heads will prevail. 

Differential-K is a very bold theory, sweeping in scope, developed by J.P. Rushton that aims to connect a wide range of apparently unrelated human variables in a single theoretical framework (Meisenberg & Woodley, 2013). According to this theory, variations in the generally preferred reproductive strategy of particular human groups have affected the during the course of their evolution. A fast life history strategy involves high mating effort and the production of a larger number of children with less intensive investment in each one. This kind of strategy is suited to conditions in which life expectancy is fairly short and infant mortality is high, and so people must aim to reproduce fairly quickly and frequently to ensure they pass on their genes to the next generation. In contrast, a slow life history strategy involves less mating effort and more parenting effort, with the production of fewer children and more intensive investment in each one. Differential-K theory assumes that fast and slow strategies are each associated with a whole suite of human characteristics that differ not only among individuals but between whole populations. Specifically, East Asian peoples are assumed to have the slowest strategy, while sub-Saharan African peoples have the fastest strategy, and Caucasian peoples are in-between, although closer to Asians than Africans. Naturally this theory has been the focus of intensely heated controversy due to its assumptions about racial differences. Supporters of this theory argue that it has the virtue of being parsimonious, as it purports to explain a wide range of disparate phenomena with a single principle (Meisenberg & Woodley, 2013). Critics have argued that it is makes arbitrary assumptions about what characteristics are supposed to be associated with fast and slow strategies respectively in order to create a hierarchy of humanness, and that Rushton and colleagues have used cherry-picked and distorted selections of evidence in support of this theory (Weizmann, Wiener, Wiesenthal, & Ziegler, 1990). Due to the breadth and complexity of the topic, I will not attempt anything like a comprehensive review here. Instead I will focus on a recent paper (Dutton, van der Linden, & Lynn, 2016) that attempts to test if racial differences in androgen levels follow a pattern predicted by differential-K theory.

According to Richard Lynn, life history strategy might be regulated by androgens (i.e. masculine hormones like testosterone) such that higher androgen levels are associated with a faster life history strategy. Higher androgen levels are associated with greater aggression and competitiveness, as well as with increased short-term mating. Populations with a slower life history strategy have historically had a greater need for cooperation among males due to the harsher environments in which they lived and this led to reduced androgen levels. Hence, Lynn proposed racial differences in androgen levels, with sub-Saharan Africans having the highest levels, followed by Caucasians, followed by East Asians. This theory implies that high androgen populations should have higher levels of interest in short-term sexual relationships (a marker of mating effort) while lower androgen populations should be more sexually restrained. Dutton, et al. (2016) aimed to test this theory by examining data on androgen indicators in a range of representative countries. The lead author of this paper, Edward Dutton, has also provided information about this research in a conference presentation that can be viewed here. I was personally interested to note that Dutton mentions my name in this presentation in regard to an article I wrote a few years ago critiquing a paper by Richard Lynn (2013) in which the latter used data from an anonymous website as evidence for race differences in penis length (see slide 5). According to Dutton, I 'ridiculed' this paper because of ‘minor mistakes’ on the website that I argued invalidated Lynn’s claims. Dutton goes on to assert that the results of his research demonstrate that ‘Lynn’s penis data can indeed be trusted.’ I still stand behind my original criticisms and respond to Dutton’s comments in the follow up to this article. In the meantime, I will see if I can keep the ridicule to a minimum, or at least stay within the bounds of civil discussion.

To test their theory, Dutton et al. identified five androgen-level indicators for which national-level data was available. One of these was CAG repeats on the AR. According to a review (Minkov & Bond, 2015), more CAG repeats are associated with androgen insensitivity, while fewer repeats are linked to more sexual partners and violent and impulsive behavior.[1] The other indicators were: amount of body hair, specifically, hair on the middle digit of the fingers (mid-phalangeal hair); national prostate cancer incidence; and two measures of sexual behavior, specifically, number of partners, and annual frequency of sex. Data on sexual behavior derived from a 2005 internet survey by Durex, the condom manufacturer. Unfortunately, because the Durex survey included only one African country[2], it was only possible to make comparisons between Caucasians and Asians. I would like to point out that this survey is not scientific and is not peer-reviewed, so the quality of its methodology is unclear. Internet surveys are not necessarily representative of the population they are derived from[3], so the results may not be valid indicators of rates of sexual behavior in the respective countries. Racial categories were decided based on the main group within each country. For Dutton et al.'s purposes, Northeast Asian (e.g. China) and Southeast Asian (e.g. Malaysia) countries were classified as East Asian (or just Asian for brevity), while European, North African and several South-Asian (e.g. India) countries were classified as Caucasian. Sub-Saharan African countries were classified as such, and simply referred to as African for brevity.

I will briefly summarise the results and then provide some comments. The five androgen indicators were correlated in the expected directions with each other, and 7 out of 10 of the correlations were significant. The authors argue that these inter-correlations support their hypothesis that these are actually manifestations of androgen levels. Although not mentioned in the published paper, Dutton’s conference presentation notes that the five androgen indicators were correlated with the penis length data used by Lynn. He asserts that because all these measures are correlated with each other that this ‘demonstrates that Lynn’s penis data can indeed be trusted’ (slide 7).

To show the outcomes for the group comparisons I have adapted the authors’ results into the table below.

Group Comparison of the Androgen Indicators
East Asians
Sub-Saharan Africans
AR CAG length
N countries
Androgenic hair
N countries
Prostate cancer
N countries
Sex frequency
N countries
Sex partners
N countries

In line with the authors’ expectations, statistical tests showed that East Asian populations had lower androgen markers than Caucasians on all five indicators. However, the remaining results were not in line with differential-K theory because African populations did not have significantly higher androgen markers than Caucasian ones on any measure. For AR CAG length, the difference between Caucasians and Africans was in the expected direction but was not statistically significant, although both groups had greater CAG lengths than Asians. Africans had significantly lower rates of prostate cancer than Caucasians (and did not significantly differ from Asians) and the lowest percentage of androgenic hair.   

To recap, differential-K theory predicts that African populations should have the highest levels of androgens, followed by Caucasians, followed by Asians, and that Caucasians should be closer to Asians than Africans. Of the three comparisons that included Africans, only the results for AR CAG repeats come close to this pattern, although the difference between Africans and Caucasians was not significant, and Caucasians were actually slightly closer to Africans than to Asians. To be fair the non-significance of this result might be attributable to the small number (only four) of African nations in the analysis. A number of previous studies have actually found that people of African descent on average did have shorter CAG repeats than other peoples (Ackerman et al., 2012; Esteban et al., 2005; Kittles et al., 2001; Lange et al., 2008). However, whether this actually indicates anything about the life history strategy of different populations remains questionable. The two other androgen indicators for which African data was available follow a completely different pattern. For androgenic hair, Caucasians have the highest rate, followed by Asians, then Africans. For prostate cancer, Caucasians have the highest rate, followed by Asians and Africans, who do not significantly differ.

According to differential-K theory, Africans and Asians are supposed to be at opposite ends of the life history strategy continuum. However, if androgens are a marker of life history strategy, then based on two of the indicators Africans and Asians would appear to be at the slow end of the continuum and Caucasians at the fast end. This is very difficult to reconcile with differential-K theory. Dutton et al. provide no African data on sexual behavior, so they cannot say whether Africans are less restrained than Caucasians as predicted by their theory. However, they found that Africans were more similar to Asians than Caucasians on two of the androgen indicators. According to the logic used by Dutton et al., if sexual behavior is correlated with androgen levels, then it would be reasonable to expect Africans to be more like Asians in respect to sexual behavior as well. However, such a result would also be contrary to the predictions of their theory. On the other hand, the data source Dutton et al. used for sexual behavior is not a scientific one, so it might not even be valid anyway.

In my follow-up post, I discuss how Dutton et al. interpret their anomalous results, then respond to Dutton’s claims that his results support the validity of Lynn’s penis data and explain why his own results actually contradict this. My third post in this series address the issue of differences in sexual attitudes across major human populations, and shows that these do not fit the predictions of Differential-K theory.

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© Scott McGreal. Please do not reproduce without permission. Brief excerpts may be quoted as long as a link to the original article is provided. 

This article also appears on Psychology Today on my blog Unique - Like Everybody Else.

Ackerman, C. M., Lowe, L. P., Lee, H., Hayes, M. G., Dyer, A. R., Metzger, B. E., . . . The Hapo Study Cooperative Research, G. (2012). Ethnic Variation in Allele Distribution of the Androgen Receptor (AR) (CAG)n Repeat. Journal of Andrology, 33(2), 210-215. doi: 10.2164/jandrol.111.013391
Aluja, A., García, L. F., Blanch, A., & Fibla, J. (2011). Association of androgen receptor gene, CAG and GGN repeat length polymorphism and impulsive-disinhibited personality traits in inmates: the role of short-long haplotype. Psychiatric Genetics, 21(5), 229-239.
Cheng, D., Hong, C.-J., Liao, D.-L., & Tsai, S.-J. (2006). Association study of androgen receptor CAG repeat polymorphism and male violent criminal activity. Psychoneuroendocrinology, 31(4), 548-552. doi: 10.1016/j.psyneuen.2005.11.004
Comings, D. E., Muhleman, D., Johnson, J. P., & MacMurray, J. P. (2002). Parent–Daughter Transmission of the Androgen Receptor Gene as an Explanation of the Effect of Father Absence on Age of Menarche. Child Development, 73(4), 1046-1051. doi: 10.1111/1467-8624.00456

Dutton, E., van der Linden, D., & Lynn, R. (2016). Population differences in androgen levels: A test of the Differential K theory Personality and Individual Differences, 90, 289-295

Esteban, E., Rodon, N., Via, M., Gonzalez-Perez, E., Santamaria, J., Dugoujon, J.-M., . . . Moral, P. (2005). Androgen receptor CAG and GGC polymorphisms in Mediterraneans: repeat dynamics and population relationships. J Hum Genet, 51(2), 129-136.
Kittles, R., Young, D., Weinrich, S., Hudson, J., Argyropoulos, G., Ukoli, F., . . . Dunston, G. (2001). Extent of linkage disequilibrium between the androgen receptor gene CAG and GGC repeats in human populations: implications for prostate cancer risk. Human Genetics, 109(3), 253-261. doi: 10.1007/s004390100576
Lange, E. M., Sarma, A. V., Ray, A., Wang, Y., Ho, L. A., Anderson, S. A., . . . Cooney, K. A. (2008). The androgen receptor CAG and GGN repeat polymorphisms and prostate cancer susceptibility in African-American men: results from the Flint Men's Health Study. J Hum Genet, 53(3), 220-226.
Lynn, R. (2013). Rushton’s r–K life history theory of race differences in penis length and circumference examined in 113 populations. Personality and Individual Differences, 55(3), 261-266. doi:
Meisenberg, G., & Woodley, M. A. (2013). Global behavioral variation: A test of differential-K. Personality and Individual Differences, 55(3), 273-278. doi:
Minkov, M., & Bond, M. H. (2015). Genetic polymorphisms predict national differences in life history strategy and time orientation. Personality and Individual Differences, 76, 204-215. doi:
Rajender, S., Pandu, G., Sharma, J. D., Gandhi, K. P. C., Singh, L., & Thangaraj, K. (2008). Reduced CAG repeats length in androgen receptor gene is associated with violent criminal behavior. International Journal of Legal Medicine, 122(5), 367-372. doi: 10.1007/s00414-008-0225-7
Weizmann, F., Wiener, N. I., Wiesenthal, D. L., & Ziegler, M. (1990). Differential K theory and racial hierarchies. Canadian Psychology, 31(1), 1-13. doi: 10.1037/h0078934

[1] Actually, the evidence reviewed by Minkov and Bond is somewhat equivocal. One of the two studies comparing violent offenders with a community sample, found no difference between the two groups in CAG repeat length (Cheng, Hong, Liao, & Tsai, 2006) while the other one did (Rajender et al., 2008). A study looking at impulsive personality traits (Aluja, García, Blanch, & Fibla, 2011) found that although an inmate sample was higher on a range of impulsive personality traits compared to a community control group, the two groups did not differ in CAG repeat lengths. A study (Comings, Muhleman, Johnson, & MacMurray, 2002) cited by Minkov and Bond as evidence linking CAG repeats to lifetime number of sexual partners did not actually assess CAG repeats at all, but a separate structure of the AR gene called the GGC polymorphism. Additionally, the study sample consisted of men being treated for substance abuse and did not have a healthy control group. 
[2] South Africa
[3] For example, countries differ in their levels of internet access, which can affect who responds to the survey. Additionally, people who choose to respond to internet surveys, especially ones about sex, and in particular one that is hosted on the website of a condom manufacturer, may not be typical of people in the general population. The Durex website does not provide any information addressing these issues. (Thanks to Petra Boynton for highlighting these concerns.)