This story is part of National Geographic's special eight-month Future of Food series.

Rice and wheat do more than feed the world. They have also affected the way we think—in dramatically different ways.

That is the result of a study published Thursday in Science comparing people from different parts of China. Researchers led by Thomas Talhelm of the University of Virginia, Charlottesville, found that people from rice-growing regions think in more interdependent and holistic ways than do those from wheat-growing areas.

Talhelm thinks these differences arose because it takes much more cooperation and overall effort to grow rice than wheat. To successfully plant and harvest rice, farmers must work together to build complex irrigation systems and set up labor exchanges. Over time, this need for teamwork fosters an interdependent and collectivist psychology. Wheat, however, can be grown independently, so wheat farmers become more individualistic.

Talhelm found that even people from adjacent counties on either side of the Yangtze River think differently if they grow different crops. "I don't see any other theory that explains why you find these differences between people in neighboring counties," he says.

View Images NG STAFF. SOURCE: TALHELM, T., ET AL. SCIENCE

Although the team focused on China, their results may explain broader differences between countries too. East Asian nations like Japan and South Korea have a long history of rice-growing, and their populations are more interdependent and less individualistic than those of other countries with comparable wealth.

The results also show that East Asian psychology is more diverse than usually portrayed, the study says. The region is often stereotyped as a hub of interdependence, but the wheat-growing north of China showed the individualistic and analytic thought that is typically associated with the West.

"As a field, cultural psychology has only existed for around 20 years, and a lot of it has focused on contrasting East and West. People are getting tired of that," says Talhelm. "People compare Americans to ... Hong Kong? Japan? It's like a random choice. There's little consideration for the diversity that exists in East Asia, and I'm hoping this study can push [recognition of] that diversity forward."

View Images A farmer examines a crop of millet in Shaanxi Province, China. PHOTOGRAPH BY JIM RICHARDSON, NATIONAL GEOGRAPHIC CREATIVE

Testing Psychological Traits

Other scientists have drawn distinctions between the psychological effects of collaborative farming versus more individualistic pursuits like herding or fishing. In showing that different styles of farming can also influence our psychology, "this work carries that line of thought one important step further," says Richard Nisbett, a psychologist at the University of Michigan in Ann Arbor.

Talhelm came up with his "rice theory" after spending a few years as a teacher in China and noticing cultural differences between the north and south. "People in the north seemed more direct, while people in the south were more concerned about harmony and avoiding conflict," he says.

He then learned that the Yangtze River divides the country into a wheat-growing north and a rice-growing south, and both halves have stuck to their respective crops for generations.

To see if these agricultural differences led to contrasting psychological traits, Talhelm's team recruited 1,162 Han Chinese students from around the country and showed them sets of three objects, such as a train, a bus, and tracks. When asked to pair two of them together, volunteers from rice-growing regions were more likely to choose holistic pairings based on relationships (train and tracks), while those from wheat-growing areas chose analytic pairings based on abstract similarities (train and bus).

The team found these differences in adjacent areas on either side of the Yangtze, which seemed to rule out other factors like climate or language to explain the stark differences in perspective.

Other tasks were also used to measure differences, and showed similar results. When asked to draw circles to represent members of their social networks, people from rice provinces drew themselves slightly smaller than their friends, while people from wheat provinces drew themselves 1.5 millimeters bigger. And in a hypothetical scenario, people from rice provinces were more likely to reward an honest friend and less likely to punish a dishonest one—a sign of the in-group favoritism that pervades collectivist groups.

View Images Grain is winnowed in the wind in Shaanxi Province, China. PHOTOGRAPH BY JIM RICHARDSON, NATIONAL GEOGRAPHIC CREATIVE

Million-Dollar Question

By contrast, the team found no support for two other theories in cultural psychology, which tries to explain how differences in the way we think are influenced by our culture or environment. One theory suggests that as societies become wealthier and more educated, their citizens become more self-reliant and shift toward analytical, independent thought. The other posits that transmissible diseases make for more collectivist and insular populations, since interacting with strangers carries a risk of infection.

Neither trend appears true in China, where the choice of crop was the only factor that correlated with the psychological variation in the country, according to the study. Still, Talhelm doesn't want to overstate his findings: "Culture is complex and one variable isn't going to explain everything," he says.

"The results are really intriguing," says Francesca Bray, an anthropologist at the University of Edinburgh in Scotland who studies Chinese agriculture. But she added, "I'm suspicious about the psychological tests, which seem strangely simple, even ambiguous, given the heavy interpretive role they are expected to bear."

She also notes that the team studied college students in the different agricultural areas rather than actual farmers. The researchers say that cultural predispositions caused by rice-growing could persist for generations and affect people who have never farmed rice for themselves, but Bray thinks that is a sweeping statement. "I would have appreciated some suggestions about why this might be," she says.