Thursday, February 14, 2019

The Nurture of Nature



Fleet Street, watercolor by Ernest George (1839-1922). In England, middle-class families used to be so large that they overshot their niche and flooded the ranks of the lower class.



Until the last ten years it was widely believed that cultural evolution had taken over from genetic evolution in our species. When farming replaced hunting and gathering, something fundamentally changed in the relationship between us and our surroundings. We no longer had to change genetically to fit our environment. Instead, we could change our environment to make it fit us.

That view has been challenged by a research team led by anthropologist John Hawks. They found that genetic evolution actually speeded up 10,000 years ago, when hunting and gathering gave way to farming. In fact, it speeded up over a hundred-fold. Why? Humans were now adapting not only to slow-changing natural environments but also to faster-changing cultural environments, things like urban living, belief systems, and the State monopoly on violence. Far from slowing down, the pace of genetic change actually had to accelerate (Hawks et al. 2007).

These findings received a broader public hearing with the publication of The 10,000 Year Explosion: How Civilization Accelerated Human Evolution. More recently, they have been discussed in a review article by historian John Brooke and anthropologist Clark Spencer Larsen:


Are we essentially the same physical and biological beings as Ice Age hunter-gatherers or the early farming peoples of the warming early Holocene? How has the human body changed in response to nine or ten millennia of dramatic dietary change, a few centuries of public health interventions, and a few decades of toxic environmental exposures? In short, how has history shaped biology? 

[...] But very clearly human evolution did not stop with the rise of modern humanity in the Middle to Late Paleolithic. Climatic forces, dietary shifts, disease exposures, and perhaps the wider stresses and challenges of hierarchical, literate state societies appear to have been exerting selective pressure on human genetics.

In short, we have become participants in our evolution: we create more and more of our surroundings, and these surroundings influence the way we evolve. Culture is not simply a tool we use to control and direct our environment. It is a part of our environment, the most important part, and as such it now controls and directs us.

Brooke and Larsen nonetheless feel attached to older ways of evolutionary thinking, particularly the "essentialism" of pre-Darwinian biology. We see this when they assert that “the essential modeling of the genetic code ended sometime in the Paleolithic." Actually, there was no point in time when our ancestors became essentially "human"—whatever that means. A Paleolithic human 100,000 years ago would have had less in common with you or me than with someone living 100,000 years earlier or even a million years earlier. Human evolution has been logarithmic—the changes over the past 10,000 years exceed those over the previous 100,000 years, which in turn exceed those over the previous million.


Clark’s model

Brooke and Larsen discuss Gregory Clark's work on English demography. Clark found that the English middle class expanded steadily from the twelfth century onward, its descendants not only growing in number but also replacing the lower classes through downward mobility. By the 1800s, its lineages accounted for most of the English population. Parallel to this demographic expansion, English society shifted toward "middle class" culture and behavior: thrift, pleasure deferment, increased future orientation, and unwillingness to use violence to settle personal disputes (Clark, 2007). 

Clark’s work is criticized by Brooke and Larsen on two grounds:

[... ] there is no biological evidence to support an argument for English industrial transformation via natural selection. More importantly, this was a process that—hypothetically—had been at work around the world since the launch of social stratification in the Late Neolithic and the subsequent rise of state societies.

How valid are these criticisms? Let me deal with each of them.


Is social stratification the only precondition of Clark’s model?

First, it is true that many societies around the world are socially stratified, but social stratification is only one of the preconditions of Clark’s model. There are two others:

1. Differences in natural increase between social classes, with higher natural increase being associated with higher social status.

2. Porous class boundaries. The demographic surplus of the middle and upper classes must be free to move down into and replace the lower classes.

These preconditions are not met in most socially stratified societies. Brooke and Larsen are simply wrong when they say: "The poor died with few or no children everywhere in the world, and across vast stretches of human history." In reality, there have been many societies where fewer children were born on average to upper-class families than to lower-class families. A notable example is that of the Roman Empire, particularly during its last few centuries: upper-class Romans widely practiced abortion and contraception (Hopkins 1965). A similar situation seems to have prevailed in the Ottoman Empire. By the end of the eighteenth century, Turks were declining demographically in relation to their subject peoples, perhaps because they tended to congregate in towns and were more vulnerable to the ravages of plague and other diseases (Jelavich and Jelavich, 1977, pp. 6-7)

Nor are class boundaries always porous. Social classes often become endogamous castes. This can happen when a social class specializes in "unclean" work, like butchery, preparation of corpses for burial, etc. This was the case with the Burakumin of Japan, the Paekchong of Korea, and the Cagots of France (Frost 2014). Because of their monopoly over a despised occupation, they were free from outside competition and thus had the resources to get married and have enough children to replace themselves. This was not the case with the English lower classes, who faced competition from “surplus” middle-class individuals between the twelfth and nineteenth centuries. Such downward mobility is impossible in caste societies, where “surplus” higher-caste individuals are expected to remain unmarried until they can find an appropriate social situation. 

A caste society thus tends to be evolutionarily stagnant. Lower castes in particular tend to preserve mental and behavioral predispositions that would otherwise be removed from the gene pool in a more fluid social environment.

Why did class boundaries remain porous in England? The reason was probably the greater individualism of English society, particularly its expanding middle class. Sons were helped by their parents, but beyond a certain point they were expected to shift for themselves. My mother’s lineage used to be merchants on Fleet Street in London. They were successful and had such large families that they overshot their niche. By the nineteenth century, some of them had fallen to the level of shipbuilding laborers, and it was as such that they came to Canada.


Is biological evidence lacking for Clark's model?

Brooke and Larsen are on firmer ground when they say that Clark's model is unsupported by biological evidence. There is certainly a lack of hard evidence, but the only possible hard evidence would be ancient DNA. If we could retrieve DNA from the English population between the 12th and 19th centuries, would we see a shift toward alleles that support different mental and behavioral traits? That work has yet to be done. 

Nonetheless, a research team led by Michael Woodley has examined ancient DNA from sites in Europe and parts of southwest and central Asia over a time frame extending from 4,560 and 1,210 years ago. During that time frame, alleles associated with high educational attainment gradually became more and more frequent. The authors concluded: "This process likely continued until the Late Modern Era, where it has been noted that among Western populations living between the 15th and early 19th centuries, those with higher social status […] typically produced the most surviving offspring. These in turn tended toward downward social mobility due to intense competition, replacing the reproductively unsuccessful low-status stratum […] eventually leading to the Industrial Revolution in Europe" (Woodley et al. 2017).

Again, work remains to be done, particularly on the genetic profile of the English population between the twelfth and nineteenth centuries, but the existing data do seem to validate Clark's model for European societies in general. Indeed, psychologist Heiner Rindermann presents evidence that mean cognitive ability steadily rose throughout Western Europe during late medieval and post-medieval times. Previously, most people failed to develop mentally beyond the stage of preoperational thinking. They could learn language and social norms but their ability to reason was hindered by various impediments like cognitive egocentrism, anthropomorphism, finalism, and animism (Rindermann 2018, p. 49). From the sixteenth century onward, more and more people reached the stage of operational thinking. They could better understand probability and cause and effect and could see things from the perspective of another person, whether real or hypothetical (Rindermann 2018, pp. 86-87).

As the “smart fraction” became more numerous, it may have reached a threshold where intellectuals were no longer isolated individuals but rather communities of people who could interact and exchange ideas. This was one of the hallmarks of the Enlightenment: intellectuals were sufficiently large in number to meet in clubs, “salons,” coffeehouses, and debating societies.



References

Brooke, J.L. and C.S. Larsen. (2014).The Nurture of Nature: Genetics, Epigenetics, and Environment in Human Biohistory. The American Historical Review 119(5): 1500-1513

Clark, G. (2007). A Farewell to Alms. A Brief Economic History of the World. Princeton University Press: Princeton and Oxford.

Clark, G. (2009a). The indicted and the wealthy: surnames, reproductive success, genetic selection and social class in pre-industrial England.

Clark, G. (2009b). The domestication of man: The social implications of Darwin. ArtefaCTos 2: 64-80. 

Cochran, G. and H. Harpending. (2009). The 10,000 Year Explosion: How Civilization Accelerated Human Evolution. New York: Basic Books. 

Frost, P. (2014). Burakumin, Paekchong, and Cagots. ResearchGate

Hawks, J., E.T. Wang, G.M. Cochran, H.C. Harpending, and R.K. Moyzis. (2007). Recent acceleration of human adaptive evolution. Proceedings of the National Academy of Sciences (USA) 104: 20753-20758.

Hopkins, K. (1965). Contraception in the Roman Empire. Comparative Studies in Society and History 8(1): 124-151.

Jelavich, C. and B. Jelavich. (1977). The Establishment of the Balkan National States, 1804-1920. Seattle: University of Washington Press.

Rindermann, H. (2018). Cognitive Capitalism. Human Capital and the Wellbeing of Nations. Cambridge University Press.

Woodley, M.A., S. Younuskunju, B. Balan, and D. Piffer. (2017). Holocene selection for variants associated with general cognitive ability: comparing ancient and modern genomes. Twin Research and Human Genetics 20(4): 271-280.

Tuesday, February 5, 2019

Did cold seasonal climates select for cognitive ability?




Paleolithic artefacts (Wikicommons). The northern tier of Eurasia saw an explosion of creativity that pre-adapted its inhabitants for later developments.



The new journal Psych will be publishing a special follow-up issue on J. Philippe Rushton and Arthur Jensen's 2005 article: "Thirty Years of Research on Race Differences in Cognitive Ability." The following is the abstract of my contribution. The article will appear later.


The first industrial revolution. Did cold seasonal climates select for cognitive ability?

Peter Frost

Abstract: In their joint article, Rushton and Jensen argued that cognitive ability differs between human populations. But why are such differences expectable? Their answer: as modern humans spread out of Africa and into the northern latitudes of Eurasia, they entered colder and more seasonal climates that selected for the ability to plan ahead, since they had to store food, make clothes, and build shelters for the winter. 

This explanation has a long history going back to Arthur Schopenhauer. More recently, it has been supported by findings from Paleolithic humans and contemporary hunter-gatherers. Tools become more diverse and complex as effective temperature decreases, apparently because food has to be obtained during limited periods of time and over large areas. There is also more storage of food and fuel and greater use of untended traps and snares. Finally, shelters have to be sturdier, and clothing more cold-resistant. The resulting cognitive demands fall on both men and women. Indeed, because women have few opportunities to get food through gathering, they specialize in more cognitively demanding tasks like garment making, needlework, weaving, leatherworking, pottery, and use of kilns. The northern tier of Paleolithic Eurasia thus produced the "first industrial revolution"—an explosion of creativity that pre-adapted its inhabitants for later developments, i.e., agriculture, more complex technology and social organization, and an increasingly future-oriented culture. Over time these humans would spread south, replacing earlier populations that could less easily exploit the possibilities of the new cultural environment. 

As this cultural environment developed further, it selected for further increases in cognitive ability. In fact, mean intelligence seems to have risen during historic times at temperate latitudes in Europe and East Asia. There is thus no unified theory for the evolution of human intelligence. A key stage was adaptation to cold seasonal climates during the Paleolithic, but much happened later.



References

Rushton, J.P. and A.R. Jensen. (2005). Thirty years of research on race differences in cognitive ability. Psychology, Public Policy, and Law 11(2): 235-294.


Monday, January 28, 2019

Evolution of empathy, part II



Medical students, Monterrey (credit: Daniel Adelrio, Wikicommons). Mexicans feel more empathy if they have a university degree. Does university make people more empathic?



We differ from individual to individual in our capacity not only to understand how others feel but also to experience their pain or joy. This “affective empathy” also differs between the sexes, being stronger in women than in men. Does it also differ between human populations? It should, for several reasons: 

- Affective empathy is highly heritable. A recent study put its heritability at 52-57% (Melchers et al. 2016).

- It differs in adaptiveness from one cultural environment to another, being adaptive in high-trust cultures and maladaptive in low-trust ones. There has thus been a potential for gene-culture coevolution.

- Such an evolutionary scenario would require relatively few genetic changes. Affective empathy exists in all human populations, and most likely already existed in ancestral hominids. Differences within our species are thus differences in fine-tuning of an existing mechanism. 

One can imagine the following scenario:

1. Initially, affective empathy existed primarily in women and served to facilitate the mother-child relationship.

2. Later, when human societies grew beyond the size of small kin groups, this mental trait took on a new task: regular interaction with people who were not necessarily close kin.

3. Selection thus increased the capacity for affective empathy in both sexes but more so in men.

4. This gene-culture evolution went the farthest in high-trust cultures.


Affective empathy and educational level in Mexico

To measure differences in affective empathy between human populations we can administer tests like "Pictures of Facial Affect" and the "Cambridge Behavior Scale." The first test is a measure of the ability to recognize emotion in human faces. The second test is a questionnaire with responses on a 4-point scale ranging from "strongly agree" to "strongly disagree."

In a recent study from Mexico these tests confirmed that affective empathy is stronger in women than in men. There were also differences by occupational status:

[...] we sought to explore facial emotion recognition abilities and empathy in administrative officers and security guards at a center for institutionalized juvenile offenders. One hundred twenty-two Mexican subjects, including both men and women, were recruited for the study. Sixty-three subjects were administrative officers, and 59 subjects were security guards at a juvenile detention center. Tasks included "Pictures of Facial Affect" and the "Cambridge Behavior Scale." The results showed that group and gender had an independent effect on emotion recognition abilities, with no significant interaction between the two variables. Specifically, administrative officers showed higher empathy than security guards. Moreover, women in general exhibited more empathy than men. (Quintero et al. 2018)

Why were the guards less able to recognize signs of distress or happiness on human faces? The authors offer no explanation but do note that the two groups differed in educational level: most of the administrative officers were university graduates, whereas the guards had gone no farther than middle school. 

In Mexico, educational level correlates with European admixture (Martinez-Marignac et al. 2007). Is this group difference in empathy really an ethnic difference?


The amygdala and political orientation in the U.S. and the U.K.

Tests are subjective and thus suffer from biases that may produce different results in different populations. To avoid this problem, a promising method is to measure the size or activity of brain structures that are associated with affective empathy. In the latest review of the literature, Tal Saban and Kirby (2019) assign the amygdala a key role:

Neuroscientists have identified the brain regions for the "empathy circuit": 1) the amygdala, responsible for regulating emotional learning and reading emotional expressions; 2) the anterior cingulate cortex (ACC), activated during observed or experienced pain in the self or others; and 3) the anterior insula (AI), which responds to one's pain and the pain of a loved one (Carr, Iacoboni, Dubeau, Mazziotta, & Lenzi, 2003). In recent years the mirror neuron system (MNS), comprised of the inferior frontal gyrus and inferior parietal cortex, has been suggested to also be involved in empathy (Gazzola et al., 2006, Kaplan and Iacoboni, 2006, Pfeifer et al., 2008, Baird et al., 2011). The broad notion that empathy involves "putting oneself in another's shoes" by simulating what others do, think, or feel, has been linked to the properties of mirror neurons.

The amygdala has been linked to affective empathy by MRI studies on healthy individuals and on individuals with amygdala lesions (Bzdok et al. 2012; Brunnlieb et al. 2013; Gu et al. 2010; Hurlemann et al. 2010; Leigh et al. 2013).

Two studies have found group differences in amygdala size or activity. When brain MRIs were done on 82 adults from the University of California at San Diego, the right amygdala showed more activity in Republicans than in Democrats (Schreiber et al., 2013). Similarly, a study of 90 adults from University College London found that the right amygdala was larger in self-described conservatives than in self-described liberals (Kanai et al., 2011).

Is affective empathy stronger in conservatives than in liberals? Or are these labels a proxy for something else? In both the United States and England, party politics is increasingly identity politics. While it is true that non-European minorities tend to be socially conservative, they nonetheless tend to be politically liberal, often overwhelmingly so. In the American study, party affiliation was undoubtedly the dimension being measured: participants were asked whether they were Democrat or Republican. This is less evident in the English study, where participants were asked about their "political orientation."

Both universities are ethnically diverse. University of California at San Diego is 36% Asian, 20% White, 19% non-resident alien, and 17% Latino (Anon 2019). There is no ethnic breakdown of University College students, but we know that a third of them come from outside the United Kingdom (Wikipedia 2019).


Conclusion

Brain MRIs provide a means to measure affective empathy objectively. We can thus evaluate differences between human populations, just as we have evaluated differences between men and women, and from individual to individual. This kind of comparative research will likely be done by accident rather than by design, as with the above three studies.

Another approach would be to identify alleles that correlate with a high level of affective empathy. A polygenic score could then be created, thus providing an objective yardstick for measuring this mental trait in any human population. Particularly promising are two polymorphisms. Alleles at the OXTR gene correlate with inter-individual differences in empathy, especially with affective empathy in women (Huetter et al. 2016). Alleles at the GNAS gene correlate with inter-individual differences in cognitive empathy, but only in women (Huetter et al. 2018).


References

Anon. (2019). University of California - San Diego, Ethnic Diversity.

Bzdok, D., L. Schilbach, K. Vogeley, et al. (2012). Parsing the neural correlates of moral cognition: ALE meta-analysis on morality, theory of mind, and empathy. Brain Structure and Function 217(4):783-796. 

Brunnlieb, C., T.F. Munte, C. Tempelmann, and M. Heldmann. (2013). Vasopressin modulates neural responses related to emotional stimuli in the right amygdala. Brain Research 1499:29-42. 

Gu, X., X. Liu, K.G. Guise, et al. (2010). Functional dissociation of the frontoinsular and anterior cingulate cortices in empathy for pain. Journal of Neuroscience 30:3739-3744. 

Huetter, F.K., H.S. Bachmann, A. Reinders, D. Siffert, P. Stelmach, D. Knop, et al. (2016). Association of a Common Oxytocin Receptor Gene Polymorphism with Self-Reported 'Empathic Concern' in a Large Population of Healthy Volunteers. PLoS ONE 11[7]:e0160059

Huetter, F.K, P.A. Horn, and W. Siffert. (2018). Sex-specific association of a common GNAS polymorphism with self-reported cognitive empathy in healthy volunteers. PLoS ONE 13(10): e0206114. 

Hurlemann, R., A. Patin, O.A. Onur, et al. (2010). Oxytocin enhances amygdala-dependent, socially reinforced learning and emotional empathy in humans. Journal of Neuroscience 30(14):4999-5007. 

Kanai, R., T. Feilden, C. Firth, and G. Rees. (2011). Political orientations are correlated with brain structure in young adults. Current Biology 21: 677 - 680.

Leigh, R., K. Oishi, J. Hsu, et al. (2013). Acute lesions that impair affective empathy. Brain 136(8):2539-2549.

Martinez-Marignac, V.L., A. Valladares, E. Cameron, A. Chan, A. Perera, R. Globus-Goldberg, N. Wacher, J. Kumate, P. McKeigue, D. O'Donnell, M.D. Shriver, M. Cruz, and E.J. Parra. (2007). Admixture in Mexico City: implications for admixture mapping of Type 2 diabetes genetic risk factors. Human Genetics 120(6): 807-819.

Melchers, M., C. Montag, M. Reuter, F.M. Spinath, and E. Hahn. (2016). How heritable is empathy? Differential effects of measurement and subcomponents. Motivation and Emotion 40(5): 720-730. 

Quintero, L.A.M., J. Muñoz-Delgado, J.C. Sánchez-Ferrer, A. Fresán, M. Brüne, and I. Arango de Montis.  (2018). Facial Emotion Recognition and Empathy in Employees at a Juvenile Detention Center. International Journal of Offender Therapy and Comparative Criminology 62(8) 2430-2446.

Schreiber, D., Fonzo, G., Simmons, A.N., Dawes, C.T., Flagan, T., et al. (2013). Red Brain, Blue Brain: Evaluative Processes Differ in Democrats and Republicans. PLoS ONE 8(2): e52970.

Tal Saban, M. and A. Kirby. (2019). Empathy, social relationship and co-occurrence in young adults with DCD. Human Movement Science 63: 62-72

Wikipedia (2019). University College London.

Monday, January 21, 2019

The evolution of empathy



Maria Walpole and her daughter Elisabeth Laura (1762), by Joshua Reynolds. Affective empathy may have initially evolved to facilitate the mother-child relationship. 


Empathy is key to the functioning of high-trust cultures. If everyone is empathic toward each other, there is no need to waste energy on self-protection or on double-checking every single transaction. Just as importantly, you can make transactions that would otherwise be uneconomical.

Empathy, however, has to be reciprocated. Otherwise, it will divert your limited resources to people who will never reciprocate and who will, in fact, bleed you dry.  

The adaptiveness of empathy therefore depends on the cultural environment. Some cultures will favor it but not others. Does it follow, then, that some human populations have become more empathic than others? Can this mental trait undergo gene-culture coevolution?

It can, if three pre-conditions are met:

1. The trait varies in adaptiveness from one culture to another.

2. The trait is genetically heritable.

3. The trait can easily evolve out of pre-existing traits, i.e., only a few genetic changes are needed.

Evolutionary psychologists will argue that modern humans have not existed long enough to evolve new mental adaptations, particularly since their expansion out of Africa and into new natural and cultural environments. There has only been fine-tuning of existing adaptations (Tooby, Cosmides, and Barkow 1992). This argument is debatable:

Even if 40 or 50 thousand years were too short a time for the evolutionary development of a truly new and highly complex mental adaptation, which is by no means certain, it is certainly long enough for some groups to lose such an adaptation, for some groups to develop a highly exaggerated version of an adaptation, or for changes in the triggers or timing of that adaptation to evolve. That is what we see in domesticated dogs, for example, who have entirely lost certain key behavioral adaptations of wolves such as paternal investment. Other wolf behaviors have been exaggerated or distorted. (Harpending and Cochran 2002)

Empathy can thus differ between human populations if the differences arise from simple changes to an existing mechanism.

So does empathy meet the above preconditions?



Differences in adaptiveness

All cultures have rules of one sort or another. These rules are enforced by external sanctions (shaming by the community, especially by family members) and internal sanctions (feelings of guilt). Most cultures rely primarily on shaming. Some cultures, particularly in Europe, rely much more on feelings of guilt. Guilt is a subset of empathy. As the wrongdoer, you transfer to yourself the feelings of the person you have wronged. You feel the pain you have inflicted, and you will now mentally punish yourself.

The anthropologist Ruth Benedict described the differences between shame and guilt:

True shame cultures rely on external sanctions for good behavior, not, as true guilt cultures do, on an internalized conviction of sin. Shame is a reaction to other people's criticism. A man is shamed either by being openly ridiculed and rejected or by fantasying to himself that he has been made ridiculous. In either case, it is a potent sanction. But it requires an audience or at least a man's fantasy of an audience. Guilt does not. In a nation where honor means living up to one's own picture of oneself, a man may suffer from guilt though no man knows of his misdeed and a man's feeling of guilt may actually be relieved by confessing his sin. (Benedict 1946, p. 223)

Shame seems to be evolutionarily older than guilt. Sigmund Freud speculated that feelings of guilt arose as a mechanism to punish misbehavior in larger communities where paternal authority is insufficient: 

When an attempt is made to widen the community, the same conflict is continued in forms which are dependent on the past; and it is strengthened and results in a further intensification of the sense of guilt. [...]. What began in relation to the father is completed in relation to the group. If civilization is a necessary course of development from the family to humanity as a whole, then [...] there is inextricably bound up with it an increase of the sense of guilt, which will perhaps reach heights that the individual finds hard to tolerate. (Freud 1962, pp. 79-80)

East Asians might seem to be an exception to this evolutionary trend. They generally live in large communities where paternal authority is insufficient to enforce social rules. This problem seems to have been resolved through a stronger sense of social duty, rather than a greater propensity for empathy and guilt.

We see this in a study of young Chinese adults. The participants could see things from another person's perspective and understand how that person felt, but they did not seem to internalize those feelings and experience them vicariously. They were motivated to obey social rules by a sense of duty, rather than by empathy and feelings of guilt: "taking the views of others is an essential duty, and the lack of consideration to others' perspectives is generally regarded as a lack of virtue in the Chinese culture" (Siu and Shek 2005).


Heritability

First, we should keep in mind that empathy is not a unitary construct. It has different components:

Pro-social behavior: willingness to help others

Cognitive empathy:  capacity to understand how others feel

Affective or emotional empathy: involuntary transference of another person's feelings to yourself, i.e., feeling that person's pain or joy.

The last component is usually what we mean by empathy. Nonetheless, a person can be low in affective empathy while being high in cognitive empathy; this is in fact the hallmark of the sociopath, i.e., a person who understands how others feel and knows how to exploit those feelings for personal gain. Of the three kinds of empathy, pro-social behavior seems the most divergent and shares the least mental circuitry with the other two. Cognitive and affective empathy share circuits that specialize in representing another person's thoughts and intensions; affective empathy seems to be an additional step where these representations are relayed to brain regions that produce the corresponding emotional responses (Carr et al. 2003; Krishnan et al. 2016).

The latest review of the literature concluded that all three components of empathy have moderate to high heritability (Chakrabarti and Baron-Cohen 2013). Since then, an adult twin study has estimated the heritability of affective empathy at 52-57% and that of cognitive empathy at 27%. The rest of the variance was largely due to non-shared environment (Melchers et al. 2016). 

These findings are in line with those of a longitudinal twin study of children from 7 to 12 years of age. Genetic influences accounted for most of the variance in callousness/unemotionality, and environmental influences were entirely non-shared (Henry et al. 2018). Other studies have shown that the capacity for affective empathy remains stable as a child develops, while cognitive empathy progressively increases (Decety et al. 2017):

Finally, men and women seem to differ in affective empathy but not in cognitive empathy: “females do indeed appear to be more empathic than males [but] [t]hey do not appear to be more adept at assessing another person's affective, cognitive, or spatial perspective” (Hoffman 1977). This sex difference has been confirmed by recent studies, notably a British study (Baron-Cohen and Wheelwright 2004), a largely Argentinean study (Baez et al. 2017), an Italian twin study (Toccaceli et al. 2018), and a Chinese study (Liu et al. 2018). The size of the sex difference varied, however, being slight in the British and Argentinean studies, large but not significant in the Italian study, and significant in the Chinese study. 


Evolution in Homo sapiens

Affective empathy seems to be universal in our species. Differences do exist, however, between individuals, and these differences are distributed along a Bell curve in a human population (Baron-Cohen 2011; McGregor 2018). Any distinction between “normal people” and “sociopaths” is therefore arbitrary. There is simply a continuum of decreasing capacity for affective empathy.

Affective empathy also differs between men and women, and this sex difference seems, in turn, to differ from one population to another. This last point suggests an evolutionary pathway. Affective empathy may have initially evolved in ancestral humans as a means to facilitate the mother-child relationship. "Guilt cultures" then favored extension of affective empathy to a wider range of social interactions, as well as increased expression in men. One consequence would be a smaller sex difference in this mental trait.

How do guilt cultures ensure that affective empathy is reciprocated? They seem to resolve this problem by defining themselves much more as moral communities than as communities of related individuals. Adherence to social rules defines community membership, and these rules are perceived as being universal and absolute, as opposed to the situational morality of communities defined solely by kinship. Guilt cultures are also highly ideological. Community members monitor not only outward behavior for compliance but also inward thoughts—and this monitoring can target not just the thoughts of other members but also one’s own. Non-compliance can lead to a member being branded as morally worthless and expelled from the community (Frost 2017).

The current evidence is suggestive but not conclusive. As Baez et al. (2017) point out, most of our evidence on sex differences in empathy comes from self-report, i.e., questionnaires that men and women fill out. Many studies also fail to distinguish between cognitive empathy (understanding what others feel) and affective empathy (feeling what others feel). To measure affective empathy objectively, especially when comparing people from different cultural backgrounds, it would be best to use brain fMRIs (Krishnan et al. 2016).


To be cont'd


References

Baez, S., Flichtentrei, D., Prats, M., Mastandueno, R., García, A.M., Cetkovich, M., et al. (2017). Men, women...who cares? A population-based study on sex differences and gender roles in empathy and moral cognition. PLoS ONE 12(6): e0179336. https://doi.org/10.1371/journal.pone.0179336

Baron-Cohen, S. (2011). The Empathy Bell Curve. Phi Kappa Phi Forum; Baton Rouge 91(1): 10-12.

Baron-Cohen, S. and S. Wheelwright. (2004).The Empathy Quotient: An investigation of adults with Asperger Syndrome or high functioning autism, and normal sex differences. Journal of Autism and Developmental Disorders 34: 163-175.

Benedict, R. (1946 [2005]). The Chrysanthemum and the Sword. Patterns of Japanese Culture, First Mariner Books.

Carr, L., M. Iacoboni, M-C. Dubeau, J.C. Mazziotta, and G.L. Lenzi. (2003). Neural mechanisms of empathy in humans: A relay from neural systems for imitation to limbic areas. Proceedings of the National Academy of Sciences (USA) 100: 5497-5502.

Chakrabarti, B. and S. Baron-Cohen. (2013). Understanding the genetics of empathy and the autistic spectrum, in S. Baron-Cohen, H. Tager-Flusberg, M. Lombardo. (eds). Understanding Other Minds: Perspectives from Developmental Social Neuroscience. Oxford: Oxford University Press.

Davis, M.H., C. Luce, and S.J. Kraus. (1994). The heritability of characteristics associated with dispositional empathy. Journal of Personality 62: 369-391.

Decety, J., K.L. Meidenbauer, and J.M. Cowell. (2017). The development of cognitive empathy and concern in preschool children: A behavioral neuroscience investigation. Developmental Science 2018;21:e12570. 

Freud, S. (1962[1930]). Civilization and Its Discontents. New York: W.W. Norton

Frost, P. (2017). The Hajnal line and gene-culture coevolution in northwest Europe. Advances in Anthropology 7: 154-174.

Harpending, H., and G. Cochran. (2002). In our genes. Proceedings of the National Academy of Sciences (USA) 99(1): 10-12.

Henry, J., G. Dionne, E. Viding, A. Petitclerc, B. Feng, F. Vitaro, M. Brendgen, R.E. Tremblay, and M. Boivin. (2018). A longitudinal twin study of callous-unemotional traits during childhood. Journal of Abnormal Psychology 127(4): 374-384. 

Hoffman, M. L. (1977). Sex differences in empathy and related behaviors. Psychological Bulletin 84(4): 712-722. 

Krishnan, A., C.W. Woo, L.J. Chang, L. Ruzic, X. Gu, M. López-Solà, P.L Jackson, J. Pujol, J. Fan, and T.D. Wager. (2016). Somatic and vicarious pain are represented by dissociable multivariate brain patterns. eLife 2016;5:e15166 

Liu, J., X. Qiao, F. Dong, and A. Raine. (2018). The Chinese version of the cognitive, affective, and somatic empathy scale for children: Validation, gender invariance and associated factors. PLoS ONE 13(5): e0195268. 

McGregor, J. (2018). The highly empathic. SoRECS – The Society for Research into Empathy, Cruelty & Sociopathy. May

Melchers, M., C. Montag, M. Reuter, F.M. Spinath, and E. Hahn. (2016). How heritable is empathy? Differential effects of measurement and subcomponents. Motivation and Emotion 40(5): 720-730. 

Siu, A.M.H. and D.T. L. Shek. (2005). Validation of the Interpersonal Reactivity Index in a Chinese Context. Research on Social Work Practice 15: 118-126.

Toccaceli, V., C. Fagnani, N. Eisenberg, G. Alessandri, A. Vitale and M.A. Stazi. (2018). Adult Empathy: Possible Gender Differences in Gene-Environment Architecture for Cognitive and Emotional Components in a Large Italian Twin Sample. Twin Research and Human Genetics 21(3): 214-226

Tooby J, L. Cosmides, and J. Barkow. (1992). Introduction: Evolutionary Psychology and Conceptual Integration. In J. Barkow, L. Cosmides, and L. Tooby (eds.) The Adapted Mind: Evolutionary Psychology and the Generation of Culture, pp. 3-16, New York: Oxford Univ. Press; 1992.

Monday, January 14, 2019

Unusually diverse



Portrait “Mijke” – Frans Koppelaar (1943 - ). Europeans are unusually diverse for hair color. Over 200 alleles have been identified in British subjects.


Europeans are unusually diverse for hair color. When this diversity was being studied two decades ago, 11 nonsynonymous alleles for hair color had been identified in Europeans, versus 5 in Asians and 1 in Africans (Harding et al. 2000; Rana et al. 1999). The disparity is even greater because the Asian alleles produce pretty much the same hair color.

European hair color is unusual in another way. “Nonsynonymous alleles” make a visible difference and are usually outnumbered by those that don’t. The reverse is true, however, at the main gene for hair color, MC1R, where nonsynonymous alleles outnumber synonymous alleles by a ratio of two to one. 

Rana et al. (1999) concluded that some kind of selection had caused hair color to diversify outside Africa. Harding et al. (2000) disagreed, attributing this diversification to relaxation of selection: as humans spread out of Africa, selection for black hair grew weaker and new hair colors gradually accumulated. Of course, this scenario would require a long span of time: close to a million years to produce the current variability of hair color, including approximately 80,000 years for today's prevalence of red hair alone (Harding et al. 2000; Templeton 2002). 

That is a long time. Given that modern humans left Africa some 60,000 years ago and arrived in Europe only 45,000 years ago, some academics began to argue that Europeans must have inherited their diverse hair colors from the Neanderthals. 

A Neanderthal origin is nonetheless problematic, if only because ancestral Neanderthals and Denisovans separated from ancestral modern humans an estimated three quarters of a million years ago (Rogers et al. 2017). Well, perhaps that's close enough to the above estimate of one million years ago. Another problem: when Ding et al. (2017) examined alleles for red hair, they identified only one as being of Neanderthal origin; the others apparently arose among modern humans. Finally, even if the different alleles for hair color had been introduced through Neanderthal admixture, some kind of selection would have still been needed to increase their frequency in the European gene pool, which is only 1 to 4% of Neanderthal origin.

With enough hand-waving, one can explain the many hair colors of Europeans in terms of relaxation of selection and Neanderthal admixture... as long as there are only a dozen alleles to explain away. A recent study, however, has found a lot more:

We report here the analysis of the majority of UK Biobank, a total of almost 350,000 subjects. By performing genome-wide analyses across hair colours, we have discovered novel variation in and around MC1R that contributes to red hair. [...] Furthermore, we identify more than 200 genetic variants independently associated with multiple hair colours on the spectrum of blond to black. (Morgan et al. 2018)

More than two hundred! If these alleles were due to relaxation of selection we would have to assume they had slowly accumulated over tens of millions of years—a time span longer than the existence of all hominids. Clearly, the facts call for another explanation: some kind of selection created these numerous hair colors, and very strong selection at that. 

This selection operated relatively fast and over a relatively small geographic area, while also causing eye color to diversify at the same time. Ancient DNA shows that most Europeans had only black hair and brown eyes until seven thousand years ago, and perhaps later still. Previously, the other hair and eye colors existed only in humans from Scandinavia, the East Baltic and, apparently, areas farther east (Günther et al. 2018; Mittnik et al. 2018). 

In fact, the oldest genetic evidence of blond hair, dated to 18,000 years ago, comes from the site of Afontova Gora in central Siberia (Mathieson et al. 2018, p. 52). At sites in south-central Siberia dating from the third millennium B.C. to the fourth century A.D. we find that most individuals had blue or green eyes and blond, red, or brown hair (Bouakaze et al. 2009). This finding is consistent with old Chinese records, which mention south Siberian peoples with "green eyes" and "red hair" (Keane 1886, p. 703).

The evidence thus suggests that the current European phenotype came into being during the last ice age 10,000 to 20,000 years ago on the plains stretching from the Baltic to central Siberia. But why would a cold, open environment select for a diverse palette of hair and eye colors? Apparently, this was not natural selection by the steppe-tundra environment; it was sexual selection by the accompanying social environment, specifically a mate market where too many women had to compete for too few men. Polygyny was not an option for most men. Almost all of the food was obtained through hunting of big game (reindeer, bison, etc.), and this high meat diet made it too costly for all but the ablest hunters to support a second wife and her offspring. High male mortality further reduced the number of men available for mating. Game animals had to be pursued over long distances and unstable terrain with no alternative food sources (Frost 2006; Frost 2014; Frost, Kleisner, and Flegr 2017).

This new phenotype eventually died out in its eastern range and became confined to the northeast of Europe. From there it spread to the rest of the continent on the eve of recorded history. Only then, not long before the beginnings of ancient Greece, did most Europeans come to look European ... as if they were a cast of actors who had been made up and rushed onto the stage just moments before curtain time.


References

Bouakaze, C., C. Keyser, E. Crubézy, and D. Montagnon, and B. Ludes. (2009). Pigment phenotype and biogeographical ancestry from ancient skeletal remains: inferences from multiplexed autosomal SNP analysis. International Journal of Legal Medicine 123(4): 315-325.

Ding, Q., Y. Hu, S. Xu, C.C. Wang, H. Li, R. Zhang, et al. (2014). Neanderthal origin of the haplotypes carrying the functional variant Val92Met in the MC1R in modern humans. Molecular Biology and Evolution 31(8): 1994-2003

Frost, P. (2006). European hair and eye color - A case of frequency-dependent sexual selection? Evolution and Human Behavior 27(2): 85-103.

Frost, P. (2014). The puzzle of European hair, eye, and skin color. Advances in Anthropology 4(2): 78-88. 

Frost, P., K. Kleisner, and J. Flegr. (2017). Health status by gender, hair color, and eye color: Red-haired women are the most divergent. PLoS One 12(12): e0190238. 

Günther, T., H. Malmström, E.M. Svensson, A. Omrak, F. Sánchez-Quinto, G.M. Kilinç, et al. (2018). Population genomics of Mesolithic Scandinavia: Investigating early postglacial migration routes and high-latitude adaptation. PLoS Biol 16(1): e2003703. https://doi.org/10.1371/journal.pbio.2003703 

Harding, R.M., E. Healy, A.J. Ray, N.S. Ellis, N. Flanagan, C. Todd, et al. (2000). Evidence for variable selective pressures at MC1R. American Journal of Human Genetics 66(4): 1351-1361.

Keane, A.H. (1886). Asia with Ethnological Appendix. London: Edward Stanford.

Mathieson, I., S.A. Roodenberg, C. Posth, A. Szécsényi-Nagy, N. Rohland, S. Mallick, et al. (2018). The Genomic History of Southeastern Europe, Supplementary Information, p. 52. Nature 555: 197-203

Mittnik, A., C-C. Wang, S. Pfrengle, M. Daubaras, G. Zarina, F. Hallgren, et al. (2018). The genetic prehistory of the Baltic Sea region. Nature Communications 9(442)

Morgan, M.D., E. Pairo-Castineira, K. Rawlik, O. Canela-Xandri, J. Rees, D. Sims, A. Tenesa, and I.J. Jackson. (2018). Genome-wide study of hair colour in UK Biobank explains most of the SNP heritability. Nature Communications 9: 5271

Rana, B.K., D. Hewett-Emmett, L. Jin, B.H.J. Chang, N. Sambuughin, M. Lin, et al. (1999). High polymorphism at the human melanocortin 1 receptor locus. Genetics 151(4): 1547-1557.

Rogers, A.R., R.J. Bohlender, C.D. Huff. (2017). Early history of Neanderthals and Denisovans. Proceedings of the National Academy of Sciences 114 (37): 9859-9863, 

Templeton, A.R. (2002). Out of Africa again and again. Nature 416(6876): 45-51.