Differential K theory

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Differential K theory is a highly controversial theory by J. Philippe Rushton which aims to explain numerous argued differences between human races.


The "differential K theory" regarding argued differences between human races was originally an adaption of "r-K selection theory" (or "r/K selection theory"), which is a theory regarding differences between species.

"Life history theory" is a more general theory, which also includes aspects such as related differences between individuals and changes in strategy during an individual's life.

Race, Evolution, and Behavior

Average racial differences from Race, Evolution, and Behavior
Africans Europeans East Asians
Brain size
Cranial capacity (cubic centimeters) 1,267 1,347 1,364
Cortical neurons (millions) 13,185 13,665 13,767
IQ test scores 85 100 106
Academic achievements Lower High High
2-egg twinning (per 1000 births) 16 8 4
Hormone levels Higher Intermediate Lower
Sex characteristics Larger Intermediate Smaller
Intercourse frequencies Higher Intermediate Lower
Permissive attitudes Higher Intermediate Lower
Sexually transmitted diseases Higher Intermediate Lower
Aggressiveness Higher Intermediate Lower
Cautiousness Lower Intermediate Higher
Impulsivity Higher Intermediate Lower
Self-concept Higher Intermediate Lower
Sociability Higher Intermediate Lower
Gestation time Shorter Longer Longer
Skeletal development Earlier Intermediate Later
Motor development Earlier Intermediate Later
Dental development Earlier Intermediate Later
Age of first intercourse Earlier Intermediate Later
Age of first pregnancy Earlier Intermediate Later
Lifespan Shorter Intermediate Longer
Social organization
Marital stability Lower Intermediate Higher
Law abidingness Lower Intermediate Higher
Mental health Low Intermediate Higher
Source: Unabridged edition, Race, Evolution, and Behavior (p. 5).

The r-K selection theory is a theory which argues that different species face a trade-off between high rate of reproduction (r-strategy) and extensive care for their offspring (K-strategy). Humans may be the most K species of all.

J. Philippe Rushton applied r-K selection theory on human races and argued that human races differ regarding their degree K-strategy, which is argued to explain many racial differences.

The theory grew out of Rushton's 1989 paper, "Evolutionary Biology and Heritable Traits (With Reference to Oriental-White-Black Difference)".[1]

Rushton's book Race, Evolution and Behavior (1995, third edition 2000) compiled a very large of number of earlier studies on racial differences. Average results from these were calculated. The summarized racial differences were argued to support the theory.

Rushton argued that East Asians, Europeans, and Africans fall consistently into the same pattern when compared on a list of 60 different psychological and physical traits. The book argued that East Asians, on average, are at one end of a continuum, that Africans, on average, are at the opposite end of that continuum, and that Caucasoids are in between East Asians and Africans, but closer to East Asians.

Differences in testosterone levels or sensitivity to testosterone was proposed as a factor that may have caused many of these differences. See also Other race differences: Femininity vs. masculinity.

He further argued that Europeans and East Asians evolved more toward a K-strategy than Africans because of a colder and more predictable climate and environment. Rushton argued that the survival challenges of making warm clothes, building durable shelter, preserving food, and strategically hunting large animals all selected genes for greater intelligence and social organization among the populations that migrated to cold climates.

Rushton argued that alternative, purely environmental theories fail to elegantly explain what he sees as such a consistent pattern of both behavioral and physiological differences, and that such environmental theories instead just provide a long list of ad hoc explanations. Rushton argued that science strives to organize and simplify data, and seeks the simplest explanation possible, which he argued that his theory is (see Occam's razor).

Later supportive studies

Rushton argued that the theory was supported by relationships between brain weight and several other variables among 234 mammalian species: longevity (r = .70), gestation time (.72), birth weight (.44), litter size (-.43), age at first mating (.63), duration of lactation (.62), body weight (.44), and body length (.54). The relationship remained after controlling for body weight and body length. Looking at 21 primate species, brain size correlated even stronger at .80 to .90 with life span, length of gestation, age of weaning, age of eruption of first molar, age at complete dentition, age at sexual maturity, inter-birth interval, and body weight.[2]

Richard Lynn found support for theory in a study of sexual behaviors of Blacks and Whites in the US.[3]

Lynn has also argued that races differ in their average degree of psychopathy and that this is related to differential K differences.[4][5] See also Race and crime: Psychopathy.

Templar in a 2008 study argued that Rushton's r/K factor explained 75% of the variance for national differences in IQ, birth rate, infant mortality, HIV/AIDS, life expectancy, skin color, and GDP. "Moreover, the correlations were significantly higher with skin color, a biological variable, than they were with gross domestic product (GDP), a culturally influenced variable."[6]

Rushton and Templar in a 2009 study argued that violent crime (murder, rape, and serious assault) was lower in countries with higher IQs, higher life expectancies, lighter skin color, and lower rates of HIV/AIDS. A factor was found to explain 52% of the variance. Higher national incomes or higher rates of infant mortality did not affect the results.[7]

Also other studies on country differences have found support for the theory.[8][9][10][11][12]

Studies in several countries have found that many variables vary on a north–south gradient as predicted by the differential K theory.[13][14][15][16]

A 2015 study stated that "Differential-K theory proposes that levels of androgen, i.e. male hormone, differ across three large racial groups with Sub-Saharan Africans having the highest levels, East Asians the lowest, and Caucasians (Europeans, North Africans and South Asians) being intermediate. In this study, we found that most of the national-level indicators of androgen – CAG repeats on the AR gene, androgenic hair, prostate cancer incidence, sex frequency and number of sex partners – are positively correlated at the population (country) level. East Asians showed signs of the lowest androgen level for most indicators and were lower than Caucasians on all of them. Sub-Saharan Africans showed inconsistent results. The results provide a partial validation of Differential-K theory."[17]

A 2015 study stated that "The existence of a genetic factor behind group-level differences in life history strategy (LHS) has long been disputed. A number of recent studies suggest that some polymorphisms in the androgen receptor gene AR, the dopamine receptor gene DRD4, and the 5-HTTLPR VNTR of the serotonin transporter gene are associated with risk acceptance versus prudence and a short-term versus long-term time orientation, which are important aspects of LHS. We integrated studies from diverse nations reporting the prevalence of these three polymorphisms for many countries. We collected national indices for each of the three polymorphisms and found that they define a strong, single factor, yielding a single LHS-related, national genetic index. As expected, this index is strongly associated with reported national measures of LHS and time orientation, even after controlling for socioeconomic variables. The genetic effect seems especially strong across societies with high socioeconomic inequality."[18]

Anxiety and suicide

A 2018 study stated that "Differential-K theory, when applied to the study of anxiety disorders, predicts that slower life history (LH) racial groups exhibit higher levels of trait anxiety and worry, and higher prevalence of anxiety disorders, as both LH and anxiety experiences are future oriented. We predict that slower LH racial groups will exhibit an especially high prevalence of those anxiety disorders in which: (A) A central symptom is excessive worry rather than the anxious emotion only, as worry is an effortful cognitive phenomenon that involves mentally scrutinizing longer-term future threats and solutions; and (B) The central source of concern is social interactions, as the long-term maintenance of social relationships is one of the hallmarks of slow LH. {...] In line with the evolutionary hypothesis, Whites exhibited a higher prevalence of worry-related and sociality-related anxiety disorders than African-Americans and Latinos. Self-report data on worry and social anxiety traits further supported the evolutionary hypothesis, with Northeast Asians reporting the highest average scores. Importantly however, Blacks exhibited higher rates of post-traumatic stress disorder, a stressor-related condition, lending partial support to the social psychology hypothesis. We review and discuss racial differences in propensity to seek professional help when experiencing distress, in emotional expression to health care workers, and in the validity of psychometric measures, and conclude they are unlikely explanations for the identified race differences."[19]

Suicide may have evolutionary roots as a mechanism which in the ancestral past removed unproductive individuals, such as the elderly, from being a burden to their relatives. This would fit with a K-strategy. Voracek in a study of 75 countries found that "higher suicide rates of the total male, and female population corresponded to higher levels on the superordinate K factor from differential K theory, thought to reflect a set of mutually interrelated life history and reproductive strategy traits. Countries ranking high on suicide rates concurrently ranked high on national intelligence estimates, longevity, and affluence, whilst low on rates of births, infant mortality, HIV/AIDS, and crimes (rape, serious assault, and homicide). These findings integrate previously reported positive population-level associations between suicide rates and cognitive ability variables into the conceptual space of differential K theory."[20]

See also Political spectrum: r-K strategy.

Differential K and welfare

High K races in favor of a high degree of care may support extensive welfare systems in countries where they are predominant. However, this risks being taken advantage of by immigrants from low K races who may have many children (either within their own group or due to race mixing) who are supported by the welfare systems.

A relatively low K subgroup within a high K race may also take advantage of such welfare systems.

Differences between individuals

An extension of the theory is that individuals may differ regarding r-K-strategy or "life history strategy". This could include individuals of the same race. This would be similar to the situation for IQ, where the racial averages are different, but individual scores may differ. Thus, both individuals and groups are argued to differ regarding "speed" of life history strategy, with "slower" speed corresponding to a higher K strategy.

The "general factor of personality" has been argued to be the most important personality variable. It has been named after the general intelligence factor (g factor). A large number of studies have found support for this factor. Studies have also argued that this factor is partially heritable and related to life history theory.[21]

Strategic differentiation-integration effort theory

The "strategic differentiation-integration effort" theory states that correlations among life history traits are stronger among individuals (and groups) exhibiting faster life histories than among those with slower ones. Thus, there is argued to be larger differences between slow life history individuals (and groups), which is argued to be explained by slow life history being associated with factors such as high environmental predictability which encourages specialization into different niches. In contrast, fast life history is associated with a more unpredictably environment, therefore less specialization, and more similarity regarding various traits. Many empirical results are argued to support the theory.[22]

For example, country differences and within country regional differences are argued to follow the predictions of the theory.[23][24][25]

A 2016 study found that sexual strategies are more diverse for individuals with slower life history traits, as predicted by the theory.[26]

The Flynn effect

The life history speed of individuals and groups may to some degree be relatively quickly influenced by non-genetic factors, which would allow relatively quick changes to a more appropriate life history strategy if the environment quickly changes. An explanation for the Flynn effect is a slowing of life history speed for many groups.[27]


Race differences

Regarding race and intelligence differences, race and crime differences, and race realism, see the linked articles.

One difficulty for theory is that it is Europeans and not East Asians who have achieved most discoveries in science and technology and who achieved the scientific and industrial revolutions. This could be interpreted in various way. One is that the theory is missing important traits such as creativity, where Europeans may excel. Another is that an extreme K-strategy may have disadvantages. A third is that the East Asians were handicapped by environmental factors. Yet another is that there may be errors regarding the argued racial differences or the r–K theory argued to explain them.

In Race, Evolution and Behavior, Rushton used a methodology in which he averaged hundreds of studies, modern and historical, with equal weight regardless of the quality of the data. He argued that by averaging many studies, the results will be accurate, with the expectation being that the law of large numbers will make individual flawed results cancel one another out. This has been criticized as producing incorrect results if there is an overall bias in the data. Good data should therefore be separated from bad.[28] However, this criticism do not apply to the later peer-reviewed studies, although these do not study all of the traits studied in the book.

Rushton's studies regarding twinning, published before the book, has been criticized.[29] Also other earlier, related studies by Rushton have been criticized by another study.[30]

There have also been criticisms of the argued differences in genital size. See Race and morphology/physiology: Penis size.

A study used data from the "186-society Standard Cross-Cultural Sample" and found no statistical support for the predicted associations between "race" and behavior.[31] However, this study attempted to classify all cultures into three groups corresponding to the three races used by Rushton. For example, the Australoid cultures in Australia were classified as East Asian ("Mongoloid") cultures, which is highly questionable.

The General Factor of Personality has been criticized.[32]

Examined groups

While Rushton sometimes speaks of only three major races, it is clear that he is typically comparing certain narrower groups (Europeans, Northeast Asians, and certain Africans), and is typically not including certain other groups (such as Australoids, Amerindians, and Khoisan). This makes the argued evidence cited by Rushton more limited, but this does not prove that the theory false.

Status of r–K theory among biologists

Another criticism is that the original r–K theory regarding differences between species has by biologists been replaced by more complex life history theories, such as theories on different strategies being used during different life stages. However, such theories still incorporate many of the themes important to the r–K paradigm.[33][34]

Climate explanation

According to Rushton, the cold and harsh but predictable winters in northern regions have caused the different strategies and differences argued by the differential K theory.

One criticism of this is that the environment in Sub-Saharan Africa, for example, varies widely, which may make it dubious that all groups there would have the same evolutionary strategy. This is arguably a straw man, since Rushton acknowledges that there are different subgroups in the larger groups. Furthermore, while the environment may vary in Sub-Saharan Africa, the absence of cold and harsh winters is constant. Similar climate factors have caused all Sub-Saharan Africans to have dark skins.

The book The Nature of Race: the Genealogy of the Concept and the Biological Construct’s Contemporaneous Utility stated on the cold winters theory that this "model has interesting theoretical and empirical support. Regarding theory, in (at least some) non-human species, climate is associated with between population variation in cognition, brain size, and heritable neural functioning (see, for example: Roth et al., 2010; Roth et al., 2012; Roth et al., 2013); cold evolved populations are, apparently, sharper. For humans, models which assume a simple relationship between selection conditioned on cognitive ability and climatic harshness over the last 60,000 years reasonably predict current global cognitive capital (see: Hart, 2007; relatedly: Grall, 2012). Regarding empirical findings, climate by way of cranial size explains a non-trivial portion of the National IQ variance (see: Meisenberg and Woodley, 2013). Generally, cognitive and cognitively related somatic differences are in agreement with the cold weather model; this model is also in agreement with the literature regarding other species."[35]

Changing demographic variables and strategies

Another criticism is that whether humans choose an r-strategy or K-strategy, or similar behaviors, may depend on environmental factors without being genetically fixed. This would explain the demographic transition which refer to the observation that the number of children per person decreases as a society becomes wealthier and have less unpredictable mortality.[36] A 2004 study examined different rK strategies among different tribes of Gypsi in Serbia and argued that the different strategies observed depended on which one was most favorable in a given environment. The strategies ranged from an extreme r strategy, for humans, to more typical K strategy.[37] However, even if a strategy may be changeable to some degree depending on the environment, there may still be differences between groups regarding preferred strategy and behaviors, and some characteristics may not be possible to change.

Similarly, the theory has been criticized for ignoring demographic inconsistencies, such as fertility and infant mortality during certain time periods having been much higher in China than in European countries.[38] However, the theory applies to different evolutionary adaptations to different ancestral environments, and not necessarily to all behaviors found in the very recent environment, which may be very much different from the ancestral environment. Even a very high K group, with a tendency to lower fertility, will likely respond to high infant mortality with increased fertility in order to survive.

Alternative explanations for the racial differences

Generally, the politically correct view is that all politically sensitive racial differences are due to environmental factors. As noted earlier, Ruston's argued that his theory provides a simpler explanation than numerous ad hoc environmental explanations.

There are also alternative genetic explanations. A 1994 study by Edward M. Miller argued that "Paternal investment theory suggests that in cold climates males were selected for provisioning, rather than for mating success. In warm climates, where female gathering made male provisioning unessential, selection was for mating success. Male hunted meat was essential for female winter survival. Genes that encouraged mating success were selected for in warm (was cold) climates. Negroids (blacks) evolved in warm cold climates, while Caucasians (whites) and Mongoloids (Asians) evolved in colder climates. Mating is assisted by a strong sex drive, aggression, dominance, sociability, extroversion, impulsiveness, sensation seeking, and high testosterone. Provisioning is assisted by anxiety, altruism, empathy, behavioral restraint, gratification delay, and a long life span. Explanations are offered for racial differences in many personality characteristics, hormone levels, monamine oxidase levels, testosterone levels, lactase dehydrogenase metabolic paths, life spans, prostate cancer rates, hypertension, genital (penis and testes) size, vocal frequencies, liver size, muscle structure, mesomorphy, bone density, sports performance, crime rates, rape, child abuse, earnings, age at first sexual activity, AIDs, illegitimacy, divorce, marriage, and polygyny rates. Eye color correlations are discussed. Negro family structure in the Caribbean and the U.S. may reflect selection in Africa during hunter-gather times".[39]

External links

Race, Evolution, and Behavior


Online studies

Alternative explanations


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