What makes a person decide to recycle, carpool to work instead of driving alone or farm sustainably? Why do cultures differ in how they understand and treat the natural world? To answer those questions, psychologists are reaching across disciplinary boundaries to work with urban planners, ecologists, conservationists, product life-cycle experts and many others.

One such collaboration is between Northwestern University psychologist Douglas Medin, PhD, and Scott Atran, PhD, an anthropologist at the University of Michigan and the National Center for Scientific Research in Paris.

Since the mid-1990s, Medin and Atran have been studying cultural differences in folkbiology and folkecology--the nonscientific ways in which people categorize and reason about the natural world. Those cultural differences, they have found, can have profound effects on how people act toward the natural environment.

Such differences are also proving to be a rich source of insights into basic cognitive processes. When looking for cultural variation in how people categorize, for instance, "Biology is a natural domain to look to," says Medin. "You can't ask how people categorize Chevys and Fords in rural Guatemala because they don't have Chevys and Fords. But they do have plants and animals."

Cognition in the commons

Medin's and Atran's collaboration combines two research traditions--anthropology and cognitive psychology--whose strengths complement each other, says Atran.

"The problem with anthropologists is that what they offer for science is largely anecdotal," explains Atran. "And the problem with psychologists is that well over 95 percent of psychology experiments are done with people--especially undergraduate psychology students--at major research universities in the U.S. and Western Europe." But by combining the two approaches, says Atran, "You can get a pretty good handle on what is generalizable for humanity and what isn't."

In one long-term study spearheaded by Atran, the two have examined the folkecology of communities living in the Maya lowlands of Guatemala. One of their main interests was whether and how different cultural groups manage their communal lands for long-term sustainability.

Most economic and anthropological models, says Atran, assume that strong communal institutions are necessary to prevent the "tragedy of the commons"--a cycle of environmental degradation that occurs when individuals aren't responsible for the long-term health of common resources. But in their research among the Itza' Maya, Q'eqchi' Maya and Ladino communities of the lowlands, Atran, Medin and their collaborators found a pattern of behavior that suggests just the opposite.

"One of the striking findings from our work in Guatemala is that the Q'eqchi' Maya have many more of the social institutions in place to protect the environment, if they wanted to do that, but the Itza' Maya have relatively few," says Medin. "And yet the Itza' seem to be protecting the environment, and the Q'eqchi', at least at the moment, seem to be fairly destructive of it."

If the strength of institutions isn't responsible for the group differences in environmental behavior, then what is? Atran and Medin believe that the critical difference lies in each group's folk- ecology.

Their research suggests that the Itza' think of the natural world as a complex web of animals, plants and humans that each gain and lose from their interactions with each other. The Q'eqchi' have a much simpler, more anthropocentric view of the environment, and the Ladinos lie somewhere in the middle. Those cognitive differences are directly correlated to the quality of the natural environment that each community controls.

"We looked at mental models in these three groups and found that the Itza' have a much more reciprocal notion of the relationship between themselves and the species in their environment than the other two groups," says Atran.

Experts and undergraduates

In addition to providing insights into the tragedy of the commons, research by Medin, Atran and their collaborators has cast new light on classic findings in cognitive psychology. Their findings suggest that phenomena once considered to be universal human characteristics may instead be peculiarities of undergraduates in industrialized societies.

Their conclusion comes from research on people with expertise in various aspects of the natural world--park landscapers, professional botanists, bird watchers, fishermen and others--and from research on people from different cultural backgrounds, including American-Indian and majority-culture residents of rural Wisconsin.

That research suggests that the way people think about the natural world depends on both their level of expertise and their cultural background. Studies on undergraduates--who tend to have similar cultural backgrounds and almost no expertise with nature--can therefore be misleading, says Medin.

For example, in studies of experts, says Medin, "We typically do not get any of the reasoning phenomena that we get with undergraduates, such as central tendency effects and diversity effects--or we find that [such phenomena] are just one strategy among many."

The reason for the difference probably lies in the fact that most undergraduates have little experience with the natural world. "The most plausible idea," says Medin, "is simply that the undergraduates know so little about plants and animals that the only thing they have to rely on are these more abstract reasoning strategies."

Expertise isn't the whole story, though, notes Medin. In rural Wisconsin, majority-culture and American Indian residents engage in similar activities and have similar levels of knowledge about the natural world, but the strategies they use to think about that world differ.

"One of the striking results in our developmental studies is that 5-year-old Menominee kids seem to use ecological reasoning strategies," he explains. "We don't see that until fourth grade among majority-culture kids who have essentially the same level of experience with the natural world."

It's still too early in the research program to say exactly where those differences come from, says Medin. But there are intriguing similarities between the way the Itza' Maya and certain American Indian communities think about the environment that suggest that reciprocity--a habit of treating nonhuman species as though they were "friends and enemies, and not commodities in a shopping mall," as Atran puts it--may hold the key.