An elderly woman from the lowlands in Boliva.
In recent years, psychologists have zeroed in on five big personality traits that appear to be universal.
No matter what culture people come from, a number of studies have suggested, everyone incorporates some degree of openness, conscientiousness, extraversion, agreeableness and neuroticism.
But after considering the indigenous and mostly illiterate Tsimane forager - horticulturalists of Bolivia, researchers are challenging the idea of the "Big Five." Instead, they argue that the Tsimane have just two main personality traits: socially beneficial behavior and industriousness.
The findings call into question the universality of human personality traits. Instead, the specific demands of various societies may affect which quirks of character become most significant to different groups of people.
"Individuals in all human societies face similar goals of learning important productive skills, avoiding environmental dangers, cooperating and competing effectively in social encounters, and finding suitable mates," the researchers wrote in the Journal of Personality and Social Psychology.
But in cultures like the Tsimane, people live in small groups and their definition of what's important may be narrower and more conservative than in bigger societies. "Among the Tsimane, success is defined largely in terms of ability to produce food and provision one's family."
The Tsimane occupy the central lowlands of Bolivia, where they live in an estimated 90 villages, each ranging from 30 to 500 people. For weeks or months at a time, families go off to hunt, fish or cultivate fields before returning to their homes.
To assess the personality traits of these semi-sedentary people, scientists from the University of New Mexico and the University of California, Santa Barbara, spent nearly two years interviewing hundreds of Tsimane people and their spouses.
Results failed to show the Big Five personality traits, pointing instead to a Big Two that incorporated some of the traditional five. As the first large and rigorous study of an indigenous population, the new findings suggest that scientists need to consider a variety of cultural structures when trying to figure out how human personalities evolved.
"Any model of personality that specifies a fixed set of biologically based trait dimensions would be inconsistent with the results we report here," they wrote.
"It is in small-scale societies that humans have lived for the majority of their existence; the socioecologies of ancestral hunter - gatherers and horticulturalists are the crucible that shaped much of human psychology and behavior. We therefore urge others to conduct similar studies of personality structure in other small-scale, indigenous societies."