Lead author Michael Gurven, UCSB professor of anthropology, said that the idea that they are funneled into a relatively fixed way of interacting with the world is something we take for granted.
He said that some people are outgoing and open, others are more quiet and introverted but from an evolutionary standpoint, it doesn't really make sense that humans' dispositions differ so much, and are not more flexible.
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.
He said that considering the evolutionary adaptiveness of a trait like personality can be problematic in modern developed societies because of the widespread use of contraception.
Gurven asserted that in all animals - including humans - the better condition you're in, the more kids you have. 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.
The Tsimane present a favorable test group because their subsistence ecology is similar to the way people in developed countries lived for millennia.
Gurven said that it's a high fertility population -- the average woman has nine births over her lifetime -- and a ripe kind of population for trying to look at personality.
The study has been published online in the journal Evolution and Human Behavior.