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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)