Corollaries of Human Migration and Racial Differentiation: Stress-Tolerance and Cognitive Ability

All known extant humans are members of a single species, but there is some differentiation into groups (“races”) with such hereditable characteristics as skin color. Various secondary characteristics are statistically correlated with those initially geographic distinctions, for example skin color. Here it is proposed that ability to tolerate stress is plausibly associated with migration out of Africa into more demanding environments; and also with certain cognitive facilities since mental stress can be more difficult to manage than purely physical stress.

This suggestion has been judged too controversial for publication by several periodicals, including the Journal of Controversial Ideas. My suggestion is argued in detail in the following.

Out of Africa

It is generally agreed that Homo sapiens originated in Africa and subsequently colonized the Middle East, Europe, and Asia, as well as Pacific Islands, including Australia perhaps as early as 65,000 years ago (National Museum, n.d.).

The correlation between human skin-color and intensity of sunshine seems too obvious to be ignored, but the causative basis became understood only in the last decades of the 20^th century.

A darker skin obviously acts as a sun-screen; but why might sun-screening be advantageous?

Might it be protective against skin cancer, melanoma? But since such cancers almost always develop only in  older people who are mostly above typical reproductive age, protection against melanoma seemed an unlikely selective influence on human evolution. In the 1970s, however, a correlation was discovered between strong sunlight and a deficiency of vitamin B12, folate, which is essential for many aspects of normal metabolic processes. Protection against strong  sunshine would therefore have offered an evolutionary advantage in the regions where Homo sapiens evolved.

Sunshine is not only a hindrance to the body's supply of folate, however, it is at the same time essential for the body's production of vitamin D, which is also necessary for many normal metabolic processes. In Africa, the copious sunshine available suffices to produce the necessary amount of vitamin D even with a dark skin; but as humans migrated north, the available sunlight became too weak for the production of sufficient vitamin D when dark skin shielded the body. Evolutionary pressures therefore led to loss of skin darkness as humans migrated north and north-east (Jablonski, n.d.) where the sun’s rays were also not so strong as to threaten the production of adequate amounts of folate.

The slightly darker (“yellow”) skin tone of Mongolians, Chinese, Japanese, and Koreans may perhaps represent an optimal compromise between production of folate and vitamin D.

Correlates of Skin Color

A number of other characteristics are statistically associated with skin color.

As just pointed out, dark skin has survival advantage in Africa but not at latitudes far from the tropics. However, other characteristics statistically associated with a dark skin may not in themselves have any survival advantage. The black skin of Africans is statistically associated, for instance, with sickle-cell anemia, curly or frizzy hair, and a tendency to high blood-pressure. Somewhat hereditable traits may become statistically associated with genetic combinations that offer definite survival advantage just because the genetic combinations effecting those traits happen to lie on chromosomes in such a way that they are likely to be carried with them.

That factual caveat needs always to be kept in mind in discussions of race and racism. As Ruth Benedict pointed out long ago (Benedict, 1943), race is a matter of biology whereas racism has to do with human behavior and politics.

The obvious differences in skin color led to considering that humankind has three distinct races: African or black; East Asian or yellow; and Caucasian or white. As Benedict discusses in detail (Benedict, 1943, pp. 23-28), human traits (including skin color) are distributed rather randomly within and across racial divisions. For example, the woolly or frizzy hair common among black Africans is not shared by black Australian aborigines whose smooth wavy hair is like that of Europeans.

Blood groups, being strictly hereditary, are excellent indicators of ancestry, and their distribution across the globe is a sure sign of mixed racial ancestry from the very earliest times of Homo sapiens. For instance, aboriginal Australians have a high percentage of blood group A, which is otherwise most characteristic of Western Europe; as well as a high percentage of blood group B which is otherwise most characteristic of India and Eastern Asia. Since Australia was settled no later than 65,000 years ago, greatly mixed cross-“racial” human ancestry dates considerably further back even than that.

Racial Differences, Unique Individuals

The thesis of this article is that human migration north and east out of Africa must have been stressful, calling for invention and development of new foods and adaptation to quite different seasonal climates; that will have made tolerance of stress a beneficial trait, presumably selected for as evolution progressed. The most extreme migration on the Eurasian continent involved ancestors of the present East-Asian populations: Chinese, Japanese, Koreans. Accordingly, the race commonly described by yellow skin-color would have acquired the greatest ability to withstand stress, whereas the black African population would be least able to do so; with the white or Caucasian race in between.

Whenever such sweeping overall comparisons of races are made, it is quite essential to emphasize that distinctions observable overall between group-average or group-median values of any particular human trait are no basis at all for comparisons of individuals. Traits taken to characterize a race, population, or group are purely statistical. Every human trait is distributed widely within that group; and the distributions of different groups typically overlap to larger or smaller degree. For example, although blood group A is most characteristic of Europe and blood group B is most characteristic of Asia, any randomly selected individuals from Europe and Asia could quite likely show the opposite difference.

Again, IQ-type measures typically show statistically significant differences between racial populations. However, for individuals in the broad middle ranges of the distributions of IQ in their own group, the differences between racial groups may not show up at all for any randomly selected pair of individuals. Overall, IQ-type measures usually yield higher values for Asians, lower for blacks, and in between for Caucasians; but in any randomly selected trio of white, black, and yellow individuals, the Asian might score lowest and the black highest (Bauer, 2023).

That cognitive ability is correlated with stress-tolerance is suggested by copious data in which those two characteristics follow the same sequence in racial categories. On the common, overly simplistic classification of human races, cognitive facility or ability — typically measured by something like IQ tests — increases in the order African < Caucasian < Asian; see comprehensive reviews of the specialist literature by, for example, Herrnstein and Murray (1994) and Rushton & Jensen (2005).

Sensitivity to stress runs in the same sequence: African > Caucasian > Asian, as detailed below.

Measures of cognitive ability

That some people are “smarter” in general than others is part of common-sense experience. Although there is some disagreement over the concept of a general “cognitive ability” by contrast to independent talents for different mental activities, public controversy over racial differences is largely over how differences come about, what the consequences are, and how they would best be accommodated in society at large. Among social scientists specializing in cognitive measuring, only technicalities are controversial; it is generally accepted that there exists something like general smartness or intelligence (often termed Spearman’s “g”) which can be identified statistically and consistently through a variety of tests, and which also correlates with performance in a wide range of activities.

Public controversy has focused chiefly on the fact that population averages for measures of cognitive ability are different for the commonly used classification into human “races”; as already indicated, Asian > Caucasian > African. Herrnstein and Murray (1994) go into more detail at times: “Asian” in this sequence refers to East Asians: Chinese, Japanese, Korean, not South Asians. Further, they report consistent differentiations on IQ-type tests between verbal abilities and other, visuo-spatial or mathematical abilities; the superior performance of East Asians is on visuo-spatial matters, not verbal ones (p. 300). By contrast, the superior performance of Ashkenazi Jews on IQ-type tests, over all other groups, is owing largely to the verbal components of the tests (p. 275).

The core disagreement in public polemics has been the degree to which intelligence is inherent, genetically influenced and heritable, by contrast to developed as a result of such environmental factors as processes in the womb after conception and, thereafter, by nutritional, parental, peer, and other external influences and pressures. Herrnstein and Murray (1994), reviewing a great mass of data, suggest that the influences seem to be about equally significant.

The essential caveat, too often ignored in popular discussions, is that statistical differences in IQ and “g”, and of achievements of various sorts in a range of activities, reflect observations on groups. Such population-average measures provide no immediately useful information about individuals; as pointed out above, the distribution of measures of any given attribute among individuals in any group or population is far greater than the much smaller differences in the population-level averages between those groups. The crucial point is that these population-level averages bring no useful information whatever about any given individual, or about comparisons between individuals from different groups. Some very interesting distinctions can be identified statistically that tell nothing about any given individual. For example (Sulloway, 1996), major discoveries that fit with and expand the current paradigm, the accepted expert opinion, have been most frequently accomplished by first-born children; whereas contrarian breakthroughs have more commonly been accomplished by later- or last-born children. That rather solid statistical, group-average finding says nothing at all, however, about any given discovery; nor about any given first-born child or any given later-born sibling, in general or with any particular pair of siblings.

When population-level averages concern human races, this distinction between group and individual is critically important. 

Measures of stress

Blood pressure is a widely accepted indicator of being or feeling stressed. Below, I will also make the case for regarding the tendency to test “HIV-positive” as a general indicator of physiological stress.

Blood pressure (BP)

Many sources report that BP is characteristically higher among Africans, African-Americans, black people, than among “whites” or “Caucasians” (Lackland, 2014); a genetic basis for this has been suggested (Zilbermint et al., 2019). Among “Hispanics”, BP is higher than among “non-Hispanic whites” (Hardy et al., 2021), illustrating the fact that “Hispanic” includes both blacks and whites in varying proportions in different geographic regions.

Among Asians, BP was higher among “South Asians” than among “East/Southeast Asians” (Saeed et al., 2020).

Those and other nuances are paralleled in the “HIV”-test data discussed below, supporting the speculations that follow about human migrations and the evolution of racial distinctions.

Physiological laboratory tests that measure stress

So-called “HIV tests” do not in fact respond selectively to the presence of a Human Immunodeficiency Virus; rather, they appear to respond to quite a variety of conditions that have in common a high degree of oxidative, physiological stress. The detailed evidence for that is in a great number of publications summarized on the website “The Case against HIV” (Bauer, 2013/17), particularly in section 3, “The plain evidence about HIV”. Thus for instance:

Ø  Dozens of physiological conditions, not all of them even infections (for example, pregnancy!), correlate with high rates of “HIV-positive” — false positive test-results, in other words (3.2.2).

Ø  “AIDS”, which correlates with “HIV-positive”, reflects physiological (oxidative) stress (4.3.2.4), which is associated with the release of proteins, DNA, and other components of human cells (3.2.2.6; reference 309).

Ø  People of African heritage test “HIV-positive” at rates far higher than others: by factors of about 7 for females and about 20 for males (3.4.1). To mis-interpret this as referring to a sexually transmitted infectious agent (as the official position seems to continue to do) rests on demonstrably unwarranted racist stereotyping about sexual behavior.

Correlation of stress with Racial Category and Cognitive Ability

Both BP and “HIV-positive” mark Africans as more stress-prone than Caucasians, who are more stress-prone than Asians (as noted above, East Asians and not South Asians).

More detailed “HIV-positive” data (Bauer, 2007) point to the sequence Africans > Native Americans > Caucasians > East Asians. As to “Latino” or “Hispanic”, categories widely used in the USA, Herrnstein & Murray (1996) point out that this is neither racial nor ethnic but a varying mixture of the three more commonly used groupings; that is illustrated by “HIV-positive” data, where East-Coast “Hispanics”, who are largely of black African heritage (Puerto Rico, Haiti) test positive more frequently than West-Coast “Hispanics”, who are largely of Mexican heritage.

This is the same sequence (in reverse) as for cognitive ability, hence the speculation advanced here that cognitive ability may be connected with tolerance of stress. In that connection, it is highly pertinent that mental stress is less tolerable than purely physical stress (Graveline, n.d.).

The nuance that the measured cognitive ability of East Asians exceeds that of Caucasians on visuo-spatial but not verbal measures is also compatible with the present hypothesis. Verbal ability, the use of language, surely appeared very early in the history of Homo sapiens, perhaps even in its ancestors, almost certainly before the diaspora out of Africa. Language tasks are therefore not likely to be particularly stressful; it would only have been with more abstract and complicated mental activities that tolerance of stress became significantly important characteristics of a racial group. Migration to more difficult environments will have called for the creation and development of new ways of doing many things and will have thereby been significantly stressful mentally, psychologically.

Quite separately, the superior performance of European Ashkenazi Jews largely on measures of verbal ability may reflect the ethnic heritage of intense scholarly textual analysis, argumentation, interpretation: that people particularly talented in that direction were the most respected may, over time, have contributed to the prevalence of pertinent heritable genes in this ethnic group.

References

Bauer, H. H. (2007). The Origin, Persistence and Failings of HIV/AIDS Theory. McFarland.

Bauer, H. H. (2013/17). The case against HIV;

http://thecaseagainsthiv.net

(created October 2013, last updated December 2017).

Bauer, H. H. (2023). Groups, individuals, statistical disparities: What constitutes equity?, 22 October; https://henryhbauer.substack.com/p/groups-individuals-statistical-disparities

Benedict, R. (1943). Race and Racism, Routledge & Kegan Paul (reprinted 1983 with foreword by John Rex).

Graveline, D. (n.d.). Blood pressure, personality, and heart attack risk; https://spacedoc.com/articles/bp-personality-and-heart-attack.

Hardy, S. T., Chen, L., Cherrington, A. L., Moise, N., Jaeger, B. C,. et al. (2021). Racial and ethnic differences in blood pressure among US adults, 1999–2018. Hypertension, 78: 1730-41; doi.org/10.1161/HYPERTENSIONAHA.121.18086.

Herrnstein, R. J. & Murray, C. (1994). The Bell Curve: Intelligence and class structure in American life. Free Press (Simon & Schuster (1996 reprint with extra commentary by Murray).

Jablonski, Nina (n.d.). The evolution of skin color: Penn State anthropologist Nina Jablonski is reimagining how we look at skin color; https://www.psu.edu/impact/story/the-evolution-of-skin-color.

 Lackland, D. T. (2014). Racial differences in hypertension: implications for high blood pressure management. American Journal of Medical Science, 348: 135-38; doi: 10.1097/MAJ.0000000000000308.

National Museum of Australia (n.d.). https://www.nma.gov.au/defining-moments/resources/evidence-of-first-peoples

Rushton, J. P. & Jensen, A. R. (2005). Thirty years of research on race differences in cognitive ability. Psychology, Public Policy, and Law, 11: 235–94.

Saeed, A., Dixon, D. L., & Yang, E. (2020). Expert Analysis (Apr 06): Racial disparities in hypertension prevalence and management: a crisis control?; https://www.acc.org/latest-in-cardiology/articles/2020/04/06/08/53/racial-disparities-in-hypertension-prevalence-and-management.

Sulloway, F. J. (1996). Birth Order, Family Dynamics, and Creative Lives. Pantheon (Random House).

Zilbermint, M., Hannah-Shmouni, F., & and Stratakis, C. A.. Genetics of hypertension in African Americans and others of African descent. International Journal of Molecular Science, 20 (2019) 1081; doi: 10.3390/ijms20051081.