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Anthropologist explain evolutionary benefit of personality traits
Why this is the case and why it matters in a more traditional context are questions being addressed by anthropologists at UC Santa Barbara.
Their findings appear online in the journal Evolution and Human Behavior.
"The idea that we're funneled into a relatively fixed way of interacting with the world is something we take for granted," said Michael Gurven, UCSB professor of anthropology and the paper's lead author. Gurven is also co-director of the University of New Mexico-based Tsimane Health and Life History Project.
Gurven continued: "Some people are outgoing and open, others are more quiet and introverted. But from an evolutionary standpoint, it doesn't really make sense that our dispositions differ so much, and are not more flexible.
"Differences in personality and their relative stability are not unique to humans, and have now been studied in many species, from ants to primates. How could dispositional consistency be favored by selection?"
"If personality traits help you interact easily with bosses, find potential mates and make lots of friends, then why, over time, aren't we all extroverted?" Gurven asked.
"Successful behavioral strategies with genetic underpinnings –– and behavioral genetics has demonstrated relatively high heritability for personality variation –– often increase in frequency over time, and therefore reduce variation over many generations.
Gurven and his team wanted to examine the personality measures they had on the Tsimane adults and determine what consequences might result from one personality over another.
Gurven explained: "Considering the evolutionary adaptiveness of a trait like personality can be problematic in modern developed societies because of the widespread use of contraception. And for humans in more traditional environments, like the Tsimane, the higher your status, the better physical condition you're in, the earlier you might marry, and the higher reproductive success you're likely to have."
Based on their measurement of different aspects of personality, the researchers looked at how personality impacted the number of children men and women had. "What we found was that almost every personality dimension mattered for men, and it mattered a lot," Gurven said. "Being more extroverted, open, agreeable and conscientious –– and less neurotic –– was associated with having more kids." Interestingly, though, Gurven added, the same was not true for women.
"Because we had a large number of test subjects, we could look at whether the relationship between personality and reproduction varied across different regions of the Tsimane territory."
Some Tsimane choose to live close to town, near roads, schools and the various opportunities that accompany the more urban life, while others live in the remote headwaters, and still others live in remote forest villages where they're often isolated during much of the rainy season.
If higher fertility is the upside of extroversion and other traits, the researchers wondered what the downside might be. Looking for potential costs related to personality traits associated with higher fertility, researchers focused on health and conflicts. Neither seemed to be an issue.
"You might think that folks putting themselves out there all the time would be getting sick more often because of greater pathogen exposure or from taking risks," Gurven said. "But we didn't find much evidence that they were sicker. If anything, they were consistently healthier. Which actually makes sense when you consider that people who are in good condition in general are both healthier and more likely to be outgoing."
Health was assessed two years after the personality measurements so there was no possibility that feeling under the weather meant subjects were more likely to be shy, anxious or dispirited.
Regarding conflicts, the researchers did find that the more extroverted and open men got in trouble more often. And while conflicts can sometimes escalate into physical confrontation, Gurven added, for the most part, they don't result in death.
Researchers found no evidence that intermediate levels of extroversion or other personality traits lead to the highest fertility. Although personality varied widely between the sexes –– men scored higher on extroversion, agreableness, conscientiousness, openness, prosociality and industriousness.
"That the relationship between personality and fitness varies by sex and geographical region supports the view that fluctuating selection pressures may help maintain variation in personality," said Gurven.
Original press release: http://www.ia.ucsb.edu/pa/display.aspx?pkey=3143