Rice farming and gene-culture coevolution

 

Why didn’t alcohol intolerance evolve the same way in China as it did in southern Europe? One reason was that the Chinese have a long tradition of boiling water for drinking. So they didn’t need wine as a safe, pathogen-free alternative to water. Facial flushing, before and after (Wikicommons, Brooks et al. 2009)

 

 

In a study of 1,162 Han Chinese, a team led by Thomas Talhelm (2014) found certain psychological differences between Chinese from rice-farming regions and those from wheat-farming regions. The latter tended to be more individualistic, more analytic in their thinking, and less likely to make a big distinction between friends and strangers. Interestingly, these findings were no less true for subjects who had no connection to farming of either sort.

 

Talhelm et al. (2014) attributed these psychological differences to differences between rice farming and wheat farming:

 

The two biggest differences between farming rice and wheat are irrigation and labor. Because rice paddies need standing water, people in rice regions build elaborate irrigation systems that require farmers to cooperate. In irrigation networks, one family's water use can affect their neighbors, so rice farmers have to coordinate their water use. Irrigation networks also require many hours each year to build, dredge, and drain—a burden that often falls on villages, not isolated individuals. 

 

In comparison, wheat is easier to grow. Wheat does not need to be irrigated, so wheat farmers can rely on rainfall, which they do not coordinate with their neighbors. Planting and harvesting wheat certainly takes work, but only half as much as rice. The lighter burden means farmers can look after their own plots without relying as much on their neighbors. (Talhelm et al., 2014)

 

The term “gene-culture coevolution” isn’t mentioned, but it did cross my mind when I read that paper, and I suspect it also crossed Talhelm’s. Did rice farming favor the success of individuals who were better at rice farming? And were those individuals sometimes better because they had certain mental and behavioral tendencies?

 

That hypothesis has recently been tested in a study by Chen Zhu and other co-researchers, including Thomas Talhelm:

 

Here, we report evidence that the advent of rice domestication and cultivation may have shaped humans not only culturally but also genetically. Leveraging recent findings from molecular genetics, we construct a number of polygenic scores (PGSs) of behavioural traits and examine their associations with rice cultivation based on a sample of 4101 individuals recently collected from mainland China. (Zhu et al. 2021)

 

The polygenic scores were for height, body mass index, depression, time discounting, age at first birth, educational attainment, risk preference, and tolerance for alcohol (as measured by the ability to break it down via two enzymes: alcohol dehydrogenase and aldehyde dehydrogenase). For each mental or behavioral trait, the polygenic scores were compared with the subjects’ county of birth, specifically the county’s proportion of farmland devoted to rice paddies.

 

The trait/county correlations were then investigated for possible confounds. Because rice farming is more common in southern China, there may be confounds with latitude, temperature, certain minority groups, and so on. After controlling for these confounds, the authors found that two negative correlations remained significant: (1) age at first birth and (2) tolerance for alcohol, as measured by the ability to produce aldehyde dehydrogenase.

 

It seems, then, that people from rice-farming regions are more likely to feel sick after drinking alcohol, and that women are more likely to begin having children at a younger age. Let’s take a closer look at both findings:

 

Age at first birth

 

Rice-farming regions are associated with a younger age at first birth. Historically, rice was far more labor-intensive than wheat. The labor demands were so high that a husband and wife could not farm a large enough plot to support their family through their labor alone. Life expectancy may have also been shorter in rice-farming regions than in wheat-farming ones, with the result that the reproductive schedule was shifted toward younger ages wherever rice was primarily grown (Zhu et al. 2021). 

 

Alcohol tolerance

 

Rice-farming regions are associated with defective enzymes for alcohol tolerance. This seems to be much truer for aldehyde dehydrogenase than for alcohol dehydrogenase. Both defects reduce clearance of alcohol by the liver, but the first one has a stronger effect. In about 36% of East Asians, it causes facial flushing, nausea, and tachycardia after alcohol consumption. Not surprisingly, carriers appear to suffer less from alcoholism and alcohol-related liver disease (Brooks et al. 2009; SNPedia 2020).

 

Zhu et al. (2021) argue that selection against alcohol tolerance was stronger in rice-farming regions because rice farmers had surplus rice for wine production at an earlier date. This argument assumes that alcohol consumption was always maladaptive: once it became common, selection immediately favored individuals who couldn’t tolerate alcohol. Yet we know that alcohol consumption used to be adaptive in many parts of the world, such as southern Europe, where fermented beverages were safer to drink than water because they had no water-borne pathogens.

 

I would argue that selection against alcohol tolerance began in China when fermented beverages, notably rice wine, ceased to be the best alternative to water. Consumption of rice wine was widespread at first but later gave way to consumption of boiled water, particularly in the form of tea, during the Tang dynasty (7th to 10th centuries). There then followed a period of relative abstinence until the 19th century:

 

Following the Yangtze's incorporation into the Chinese state during the Qin dynasty, beer progressively disappeared from use over the course of the Han dynasty in favor of the stronger huangjiu and the rice wines of the southern Chinese. […] The Dutch historian Frank Dikötter describes the period between the Han and Tang dynasties as a "golden age" for alcohol […] The "rise of a tea culture during the Tang was a significant shift away from heavier patterns of intoxication".  […] Wine was reintroduced to China at Macao by Portuguese traders and missionaries, who produced small batches for communion. […] The production and its effect was minor, prior to the opening of the country by the 19th-century First and Second Opium Wars, after which European alcoholic beverages and methods of alcohol production were introduced throughout China. (Wikipedia 2022)

 

With the replacement of rice wine by tea during the Tang Dynasty, people no longer had the same need for enzymes that break down alcohol. The advantages of alcohol, in terms of preventing water-borne diseases, became outweighed by the disadvantages, in terms of alcoholism and alcohol-related diseases.

 

Thus began a long Chinese tradition of drinking hot water (Ye 2017). Rice wine, with its high alcohol content of 18-25%, became seen not only as unnecessary but also as problematic, due to the risk of alcoholism and alcohol-related diseases. Rice-farming regions may have therefore experienced a steeper decline in alcohol consumption during China’s long period of relative abstinence between the 7th and 19th centuries. If so, alcohol intolerance would be a recent evolutionary development in China’s rice-farming regions.

 

Elsewhere, as in southern Europe, people continued to drink wine as a safe alternative to water. There was thus selection for willingness to consume alcohol, but not to excess.

 

What about individualism?

 

Why didn’t Zhu’s research team look at genetic markers for individualism? Wasn’t that the main behavioral difference between rice-farming and wheat-farming regions in Talhelm’s study? The oversight is all the more puzzling because Talhelm was one of Zhu’s co-authors.

 

There is, in fact, a genetic marker for individualism: the short allele of 5-HTTLPR (Chiao and Blizinsky 2010; Schroeder et al., 2016). In addition, I would look at genetic markers for the propensity to identify social norms, to comply with them, and to ensure that others comply (Frost 2020).

 

What about cognitive ability and future orientation?

 

Zhu et al. (2021) also looked at cognitive ability (as measured by educational attainment) and future orientation (as measured, inversely, by time discounting). Cognitive ability and future orientation are both high in East Asians, but neither seem to differ significantly between Chinese from rice-farming regions and those from wheat-farming regions. In the initial results (i.e., before they were controlled for possible confounds), the first group was less future-oriented than the second, but this difference seems to be due to southern Chinese being less future-oriented than northern Chinese.

 

Things are rarely simple. No single theory can explain all the mental and behavioral differences that exist within our species. Yes, some researchers have proposed various unified theories of human biodiversity: r/k selection, selection in tropical vs. northern environments, and selection among trading vs. non-trading peoples, etc.  Each of them explains part of the picture, but none explains the whole picture.

 

There will never be a unified theory of human biodiversity, other than Darwin’s theory of evolution by natural selection. Human nature is shaped by many different selection pressures with many different causes.

 

References

 

Brooks, P.J., M-A. Enoch, D. Goldman, T-K Li, and A. Yokoyama. (2009). The Alcohol Flushing Response: An Unrecognized Risk Factor for Esophageal Cancer from Alcohol Consumption. PLoS Med 6(3): e1000050. https://doi.org/10.1371/journal.pmed.1000050  

 

Chiao, J. Y., & K.D. Blizinsky. (2010). Culture-gene coevolution of individualism-collectivism and the serotonin transporter gene. Proceedings of the Royal Society B: Biological Sciences 277: 529-537. https://doi.org/10.1098/rspb.2009.1650   

 

Frost, P. (2014). Rice farming and gene-culture co-evolution. Evo and Proud, May 31

https://evoandproud.blogspot.com/2014/05/   

 

Frost, P. (2020). The large society problem in Northwest Europe and East Asia. Advances in Anthropology 10(3): 214-134.

https://doi.org/10.4236/aa.2020.103012    

 

SNPedia (2020). rs671

https://www.snpedia.com/index.php/Rs671   

 

Talhelm, T., X. Zhang, S. Oishi, C. Shimin, D. Duan, X. Lan, and S. Kitayama. (2014). Large-scale psychological differences within China explained by rice versus wheat agriculture. Science 344: 603-607.

https://doi.org/10.1126/science.1246850   

 

Wikipedia (2022). Alcoholic drinks in China.

https://en.wikipedia.org/wiki/Alcoholic_drinks_in_China

 

Ye, F. (2017). The History of Drinking Hot Water in China (from a Cold-Water-Drinking Chinese). Radii, June 23

https://radiichina.com/the-history-of-drinking-hot-water-in-china/   

 

Zhu, C., T. Talhelm, Y. Li, G. Chen, J. Zhu, and J. Wang. (2021). Relationship between rice farming and polygenic scores potentially linked to agriculture in China. Royal Society Open Science 8(8):210382. https://dx.doi.org/10.1098%2Frsos.210382   

Do Chinese people get bored less easily?

 

Boy in a café (S. Yao, Wikicommons)

 

All humans were once hunter-gatherers. Back then, versatility came with the territory. There were only so many game animals, and they differed a lot in size, shape, and color. So you had to enjoy switching back and forth from one target animal to another. And you had to enjoy moving from one place to another. Sooner or later you'd have to.

Beginning 10,000 years ago, farmers made their appearance. Now monotony came with the territory. A plot of land wasn't something you could forget while you took off somewhere else. It needed constant care. The tasks were also more repetitive: ploughing, sowing, harvesting ...

Things worsened as farming became more advanced. You had to focus on one crop and a limited number of key tasks.

Different means of subsistence have selected for different mental traits, and this selection has had genetic consequences. Monotony avoidance has a heritability of 0.53 (Saudino, 1999). This predisposition has usually been a handicap in modern societies, so much so that it often leads to criminality. Males with a history of early criminal behavior tend to score high on monotony avoidance, as well as on sensation seeking and low conformity (Klinteberg et al., 1992).

Today, if you have trouble fitting into your society, you might still survive and reproduce. In the past, you probably wouldn’t. Other people would take your place in the gene pool and, over successive generations, their mental makeup would become the norm.

That’s gene-culture co-evolution. We have reshaped the world we live in, and this human-made world has reshaped us. After describing how our ancestors radically changed their environment, Razib goes on to write: "We were the authors of those changes, but in the process of telling that story, we became protagonists within it" (Khan, 2014).

 

China: a case study

Advanced farming—intensive land use, task specialization, monoculture—has profoundly shaped East Asian societies, particularly China. This is particularly so for rice farming. Because the paddies need standing water, rice farmers must work collectively to build, dredge, and drain elaborate irrigation networks. Wheat farming, by comparison, requires no irrigation and only half as much work.

Advanced farming seems to have favored a special package of predispositions and inclinations, including greater acceptance of monotony. This has been shown in two recent studies.

The first one was about boredom and how people experience it in their lives. The results from the 775 Chinese participants were then compared with the results from a previous survey of 572 Euro-Canadians. It was found that the Chinese participants were less likely to feel bored in comparable situations. They seemed to value low-arousal (calm, relaxation) versus high arousal (excitement, elation) in the case of Euro-Canadians (Ng et al., 2014). 

The authors attributed their findings to cultural learning. One may wonder, however, why preference for low arousal persists in the face of China’s massive influx of high-arousal Western culture.

Relational thinking, collectivism, and favoritism

The second study had the aim of seeing whether the sociological differences between rice farmers and wheat farmers have led to differences in mental makeup. When 1,162 Han Chinese performed a series of mental tasks, the results differed according to whether the participants came from rice-farming regions or wheat-farming regions (Talhelm et al., 2014).

When shown a list of three items, such as “train”, “bus”, and “tracks”, and told to choose two items that pair together, people from rice-farming regions tended to choose "train and tracks," whereas people from wheat-farming regions tended to choose "train and bus." The former seemed to be more relational in their thinking and the latter more abstract. This pattern held up even in neighboring counties along China's rice-wheat border. People from the rice side of the border thought more relationally than did people from the wheat side.

A second task required drawing pictures of yourself and your friends. In a prior study, Americans drew themselves about 6 mm bigger than they drew their friends, Europeans drew themselves 3.5 mm bigger, and Japanese drew themselves slightly smaller. In the present study, people from rice regions were more likely than people from wheat regions to draw themselves smaller than they drew their friends. On average, people from wheat regions self-inflated 1.5 mm, and people from rice regions self-deflated -0.03 mm.

A third task required imagining yourself doing business with (i) an honest friend, (ii) a dishonest friend, (iii) an honest stranger, and (iv) a dishonest stranger. This person might lie, causing you to lose money. Or this person might be honest, causing you to make money. You could reward or punish this person accordingly. A previous study found that Singaporeans rewarded friends much more than they punished them. Americans were much more likely to punish friends for bad behavior. In this study, people from rice regions were more likely to remain loyal to friends regardless.

Interestingly, these findings came from people with no connection to farming at all. They grew up in a modern urban society, and most were too young to have known the China that existed before the economic reforms of the late 1970s.  It looks like rice regions have favored hardwiring of certain psychological traits: less abstract thinking and more relational thinking, less individualism and more collectivism, and less impartiality toward strangers and more favoritism toward kin and friends.

 

Why farming sucks, for you but not for me

These findings corroborate the ethnographic literature on the differences in mentality between hunter-gatherers and farmers. Hunter-gatherers typically see farming as a kind of slavery, and they have trouble understanding well-meaning outsiders who want to turn them into land-slaves.

Yes, for the same land area, farming can produce much more food. But it's hard work, not only physically but mentally as well. Humans had to undergo a change in mentality before they could make the transition from hunting and gathering to farming

Those humans ended up transforming not just their physical landscape but also their social and cultural landscape … and ultimately themselves. By creating new values and social relations, they changed the rules for survival and reproduction, thereby changing the sort of mentality that future generations would inherit.

Humans transformed the world through farming, and the world returned the favor.

  

References

 

Khan, R. (2014). Our cats, ourselves, The New York Times, The Opinion Pages, November 24

http://www.nytimes.com/2014/11/25/opinion/our-cats-ourselves.html

Klinteberg, B., K. Humble, and D. Schalling. (1992). Personality and psychopathy of males with a history of early criminal behaviour, European Journal of Personality, 6(4), 245-266.

http://psycnet.apa.org/psycinfo/1993-18051-001
 

Ng, A.H., Y. Liu, J-Z. Chen, and J.D. Eastwood. (2014). Culture and state boredom: A comparison between European Canadians and Chinese, Personality and Individual Differences, 75, 13-18.

http://www.sciencedirect.com/science/article/pii/S0191886914006321
 

Saudino, K.J., J.R. Gagne, J. Grant, A. Ibatoulina, T. Marytuina, I. Ravich-Scherbo, and K. Whitfield. (1999). Genetic and environmental influences on personality in adult Russian twins, International Journal of Behavioral Development, 23, 375-389.

http://jbd.sagepub.com/content/23/2/375.short
 

Talhelm, T., X. Zhang, S. Oishi, C. Shimin, D. Duan, X. Lan, and S. Kitayama. (2014). Large-scale psychological differences within China explained by rice versus wheat agriculture, Science, 344, 603-607.

http://internationalpsychoanalysis.net/wp-content/uploads/2014/05/RiceversusWheatScience-2014-Talhelm-603-8.pdf

Rice farming and gene-culture co-evolution

 

Rice paddies, China, circa 1917-1923 (source). To grow rice, you must cooperate with neighbors for irrigation and labor. Today, even with the shift to a post-agricultural society, Chinese from rice-farming areas display less individualism and more interdependence than Chinese from wheat-farming areas. Is this evidence of gene-culture co-evolution?

 

Human populations differ in genetic variants that influence a wide range of mental and behavioral traits. These differences are statistical, often being apparent only when one compares large numbers of individuals. Yet even a weak statistical difference can affect the way a culture develops. Furthermore, the way a culture develops may favor certain genetic variants over others.

East Asian cultures, for example, have diverged noticeably from European cultures, particularly those of Western Europe:
 

Western culture is more individualistic and analytic-thinking, whereas East Asian culture is more interdependent and holistic-thinking. Analytic thought uses abstract categories and formal reasoning, such as logical laws of noncontradiction—if A is true, then "not A" is false. Holistic thought is more intuitive and sometimes even embraces contradiction—both A and "not A" can be true. (Talhelm et al., 2014)

This is of course a generalization that ignores differences within each culture area. Historically, abstract thinking has been stronger among the French, whereas the English have tended toward empirical "bottom-up" thinking. A new study suggests that similar differences exist within East Asia, specifically between rice-farming areas and wheat-farming areas. In short, rice farming favors interdependence, whereas wheat farming is more conducive to individualism:

The two biggest differences between farming rice and wheat are irrigation and labor. Because rice paddies need standing water, people in rice regions build elaborate irrigation systems that require farmers to cooperate. In irrigation networks, one family's water use can affect their neighbors, so rice farmers have to coordinate their water use. Irrigation networks also require many hours each year to build, dredge, and drain—a burden that often falls on villages, not isolated individuals. (Talhelm et al., 2014)

Labor inputs are thus greater for rice growing. A husband and wife cannot farm a large enough rice paddy to support their family if they rely only on their own labor. This is not the case with wheat farming:

In comparison, wheat is easier to grow. Wheat does not need to be irrigated, so wheat farmers can rely on rainfall, which they do not coordinate with their neighbors. Planting and harvesting wheat certainly takes work, but only half as much as rice. The lighter burden means farmers can look after their own plots without relying as much on their neighbors. (Talhelm et al., 2014)

A study of 1,162 Han Chinese found differences between rice-farming and wheat-farming regions on three psychological measures: cultural thought, implicit individualism, and loyalty/nepotism.

Cultural thought
 

The triad task shows participants lists of three items, such as train, bus, and tracks. Participants decide which two items should be paired together. Two of the items can be paired because they belong to the same abstract category (train and bus belong to the category vehicles), and two because they share a functional relationship (trains run on tracks). People from Western and individualistic cultures choose more abstract (analytic) pairings, whereas East Asians and people from other collectivistic cultures choose more relational (holistic) pairings.

[...] People from provinces with a higher percentage of farmland devoted to rice paddies thought more holistically. [...] Northern and southern China also differ in several factors other than rice, such as climate, dialect, and contact with herding cultures. Therefore, we analyzed differences among neighboring counties in the five central provinces along the rice-wheat border. [...] People from the rice side of the border thought more holistically than people from the wheat side of the border.  (Talhelm et al., 2014)

 

Implicit individualism

Researchers measure how large participants draw the self versus how large they draw their friends to get an implicit measure of individualism (or self-inflation). A prior study found that Americans draw themselves about 6 mm bigger than they draw others, Europeans draw themselves 3.5 mm bigger, and Japanese draw themselves slightly smaller.

People from rice provinces were more likely than people from wheat provinces to draw themselves smaller than they drew their friends. [...] On average, people from wheat provinces self-inflated 1.5 mm (closer to Europeans), and people from rice provinces self-inflated -0.03 mm (similar to Japanese). (Talhelm et al., 2014)

Loyalty/nepotism

One defining feature of collectivistic cultures is that they draw a sharp distinction between friends and strangers. A previous study measured this by having people imagine going into a business deal with (i) an honest friend, (ii) a dishonest friend, (iii) an honest stranger, and (iv) a dishonest stranger. In the stories, the friend or stranger's lies cause the participant to lose money in a business deal, and the honesty causes the participant to make more money. In each case, the participants have a chance to use their own money to reward or punish the other person.

The original study found that Singaporeans rewarded their friends much more than they punished them, which could be seen positively as loyalty or negatively as nepotism. Americans were much more likely than Singaporeans to punish their friends for bad behavior.

[...] People from rice provinces were more likely to show loyalty/nepotism [...]. In their treatment of strangers, people from rice and wheat provinces did not differ. (Talhelm et al., 2014)

Gene-culture co-evolution?

Interestingly, these findings come from people who have no connection to farming of either sort. If these psychological traits have survived the transition to a post-agricultural and largely urban society, how are they passed on? The question is raised by the authors:
 

[…] perhaps the parts of culture and thought style we measured are more resistant to change. Or perhaps modernization simply takes more generations to change cultural interdependence and thought style. However, most of our participants were born after China's reform and opening, which started in 1978. Furthermore, Japan, South Korea, and Hong Kong modernized much earlier than China, but they still score less individualistic on international studies of culture than their wealth would predict. (Talhelm et al., 2014)

The authors do not use the term "gene-culture co-evolution" but this seems to be the explanation they implicitly favor. Over many generations, rice farming has selected for a certain package of psychological traits, i.e., less abstract thinking and more functional "holistic" thinking; less individualism and more collectivism; and less impartiality toward strangers and more favoritism towards kin and friends.

The predominance of rice farming in East Asia may thus explain why East Asian cultures have developed their pattern of psychological traits:
 

The rice theory can explain wealthy East Asia's strangely persistent interdependence. China has a rice-wheat split, but Japan and South Korea are complete rice cultures. Most of China's wheat provinces devote less than 20% of farmland to rice paddies. None of Japan's 9 regions or South Korea's 16 regions has that little rice (except for two outlying islands). Japan and Korea's rice legacies could explain why they are still much less individualistic than similarly wealthy countries. (Talhelm et al., 2014)

References 

Talhelm, T., X. Zhang, S. Oishi, C. Shimin, D. Duan, X. Lan, and S. Kitayama. (2014). Large-scale psychological differences within China explained by rice versus wheat agriculture, Science, 344, 603-607.

http://www.sciencemag.org/content/344/6184/603.short