The anti-wheat movement is a popular health fad in America and critics of that staple now have a new weapon in their culture war - ditching it makes people more cooperative. And they explain Genghis Khan and Mao.

Defenders of wheat have their own ammunition - rice leads to despotism and communism. Cultural psychologists writing in Science claim that they can explain psychological differences between the people of northern and southern China mirror and also the differences between community-oriented East Asia and the more individualistic Western world - southern China has grown rice for thousands of years, whereas the north has grown wheat.

"It's easy to think of China as a single culture, but we found that China has very distinct northern and southern psychological cultures and that southern China's history of rice farming can explain why people in southern China are more interdependent than people in the wheat-growing north," said Thomas Talhelm, a University of Virginia Ph.D. student in cultural psychology and the study's lead author. He calls it the "rice theory."

Yes, the authors declare that it is simplistic to think of a billion people as a single culture so they break it into two. And then say the food is changing how they think. The team speculates that the methods of cooperative rice farming – common to southern China forever – make the culture in that region interdependent, while people in the wheat-growing north are more individualistic, a reflection of the independent form of farming practiced there over hundreds of years. 

"The data suggests that legacies of farming are continuing to affect people in the modern world," Talhelm said. "It has resulted in two distinct cultural psychologies that mirror the differences between East Asia and the West."

According to Talhelm, Chinese people have long been aware of cultural differences between the north region and the southern, which are divided by the Yangtze River – the largest river in China, flowing west to east across the vast country. People in the north are thought to be more aggressive and independent, while people to the south are considered more cooperative and interdependent.

That's why the Great Wall of China is on the river bank. 

Well, no it isn't.

And the south has had plenty of aggressive wars - but Genghis Khan has a good public relations campaign even today because the wall to keep his Mongol hordes from looting China makes him famous. However, if you visit Mongolia today, they are far less militant and aggressive than Chinese on the coast. These distinctions are oddly modern geopolitical. If you go back 700 years in Europe, you can make the same broad claims about the difference between Germans and French, except there was no France and Germany. China has 400 distinct dialects and a geography that, in the past, even the rulers in China were unclear about.

"This has sometimes been attributed to different climates – warmer in the south, colder in the north – which certainly affects agriculture, but it appears to be more related to what Chinese people have been growing for thousands of years," Talhelm said.

There is a culture war between subscription journals and open access, with legacy journals charging that open access and its editorial review and peer review lite policies lead to less rigorous papers being stamped with peer review. Claiming that rice and wheat created different psychological make-ups in people is a sign that legacy peer review isn't all that great.

notes that rice farming is extremely labor-intensive, requiring about twice the number of hours from planting to harvest as does wheat. And because most rice is grown on irrigated land, requiring the sharing of water and the building of dikes and canals that constantly require maintenance, rice farmers must work together to develop and maintain an infrastructure upon which all depend. This, Talhelm argues, has led to the interdependent culture in the southern region.

Wheat, on the other hand, is grown on dry land, relying on rain for moisture. Farmers are able to depend more on themselves, leading to more of an independent mindset that permeates northern Chinese culture.

Talhelm developed his rice idea after living in China for four years. He first went to the country in 2007 as a high school English teacher in Guangzhou, in the rice-growing south. A year later, he moved to Beijing, in the north. On his first trip there, he noticed that people were more outgoing and individualistic than in the south.

"I noticed it first when a museum curator told me my Chinese was clearly better than my roommate's," Talhelm said. "The curator was being direct and a little less concerned about how her statement might make us feel."

Presto, a cultural psychology hypothesis is born.

After three years in China doing odd jobs, he went back as a University of Virginia doctoral student on a Fulbright scholarship.

"I was pretty sure the differences I was seeing were real, but I had no idea why northern and southern China were so different – where did these differences come from?" Talhelm asked.

He soon found that the Yangtze was an important cultural divider in China. "I found out that the Yangtze River helped divide dialects in China, and I soon learned that the Yangtze also roughly divides rice farming and wheat farming," he said.

Rice farming makes people more inclined to accept despots - that explains imperial Japan as well.

He dug into anthropologiy accounts of pre-modern rice and wheat villages and realized that they might account for the different mindsets, carried forward from an agrarian past into modernity.

"The idea is that rice provides economic incentives to cooperate, and over many generations, those cultures become more interdependent, whereas societies that do not have to depend on each other as much have the freedom of individualism," Talhelm said.

He went about investigating this with his Chinese colleagues by conducting psychological studies of the thought styles of 1,162 Han Chinese college students in the north and south and in counties at the borders of the rice-wheat divide.

They found through a series of tests that northern Chinese were indeed more individualistic and analytic-thinking – more similar to Westerners – while southerners were interdependent, holistic-thinking and fiercely loyal to friends, as psychological testing has shown is common in other rice-growing East Asian nations, such as Japan and Korea.

The study was conducted in six Chinese cities: Beijing in the north; Fujian in the southeast; Guangdong in the south; Yunnan in the southwest; Sichuan in the west central; and Liaoning in the northeast.

Talhelm said that one of the most striking findings was that counties on the north-south border – just across the Yangtze River from each other – exhibited the same north/south psychological characteristics as areas much more distantly separated north and south.

"I think the rice theory provides some insight to why the rice-growing regions of East Asia are less individualistic than the Western world or northern China, even with their wealth and modernization," Talhelm said.

It will be interesting to see if this idea catches on - hopefully more scientists will learn to start using the word 'theory' correctly also.