Due to length, this post is in three parts. The second part will appear in February.

According to the controversial Differential-K theory the 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. Lynn proposed that these group differences are linked to racial differences in androgen levels (i.e. male such as ). The authors of a recent paper tried to test this theory by comparing people from different countries on rates of a number of indicators of androgen levels, including genetic markers, body hair, rates of prostate cancer, frequency and number of sex partners. Ethnic differences in these measures were found but the results did not align very well with the predictions of differential-K theory. One of the authors of this paper has claimed that these findings validate Lynn’s claims about racial differences in penis size. However, a closer look at the data contradicts this claim.

Differential-K is a very broad based theory developed by J.P. Rushton that aims to explain the relationship between a diverse range of human variables that are not obviously related using a single theoretical construct (Meisenberg & Woodley, 2013). According to this theory, during evolution human populations have varied in their generally preferred reproductive strategy. A fast life history strategy involves high 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 people must therefore aim to reproduce fairly quickly and frequently in order to ensure they pass on their genes to the next generation. In contrast a slow life history strategy involves having fewer children with 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, due to adaptations to their ancestral environments, 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 they are considered 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 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 non-scholarly sources of evidence in support of this theory (Weizmann, Wiener, Wiesenthal, & Ziegler, 1990). (I summarized these criticisms in a previous post.) 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.

Source: Spirals Galore by charcoaledsoul, used with permission under Creative Commons License

According to Richard Lynn, life history strategy could 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 and competitiveness, as well as with increased short-term mating. Lynn argues that populations with a slower life history strategy have historically had a greater need for among males due to the harsher environments in which they lived and this led to reduced androgen levels. Hence Lynn proposed that there are racial differences in androgen levels, with sub-Saharan Africans having the highest levels, followed by Caucasians, followed by East Asians. An additional implication of this theory is 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. A new study (Dutton, et al., 2016) aimed to test whether this theory is true 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 he used data from an anonymous website as evidence for race differences in penis length (see slide 5 of Dutton's presentation). According to Dutton, I ridiculed this paper because of ‘minor mistakes’ on the website that I thought 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 will respond to Dutton’s comments in my next post. 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.

Source: Wikimedia Commons

In order 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 gene. According to a review (Minkov & Bond, 2015), more CAG repeats are associated with androgen insensitivity, while fewer repeats are supposed to be linked to more sexual partners and violent and impulsive behavior. (Actually, the evidence reviewed by Minkov and Bond for these claims is much less clear than they make out.[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, it was only possible to make comparisons between Caucasians and Asians. I would like to point out that this survey is not a scientific one 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[2], so the results derived may or 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 the authors’ purposes, Northeast Asian (e. . 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 give a brief summary of 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.

Source: Adapted from Dutton et al. (2016), image created by Scott McGreal

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 do 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 explain in terms of 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. I am not asserting that this is true, just that it is more consistent with what Dutton et al. found than what is predicted by their theory. Africans being more similar to Asians on two measures also contradicts Dutton’s claims that his results support the validity of Lynn’s penis data, as the latter results were in line with the pattern predicted by Differential-K. I will discuss this in more detail in my next post.

Footnotes

[1] This is a very brief summary of the studies mentioned by Minkov and Bond: 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 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 and did not have a healthy control group. The relationship between CAG repeats and psychological characteristics is most likely very complicated.

[2] 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, e.g. here and here.)

Image credits

Spirals Galore by charcoaledsoul

The Third of May, 1808, by Francisco Goya

Related posts

Personality, Intelligence and "Race Realism" - critiques J.P. Rushton's theory

The Pseudoscience of Race Differences in Penis Size - critiques Lynn's paper on the subject

References

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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. , 21(5), 229-239.

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