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. Based on their measurement of different aspects of personality, the researchers looked at how personality impacted the number of children men and women had. 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," he said.
Study Shows How We Evolved Different Personalities
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. Only among women living in villages near town did personality associate with higher fertility, Gurven noted.
In more remote regions, the same personality profile had the opposite effect or, in some cases, no effect on fertility. For men, however, location made no difference. Wherever they lived, manifesting traits related to extroversion, openness and industriousness was associated with higher fertility. So, if higher fertility was the upside of extroversion and other traits, the researchers wondered what the downside might be.
Looking for potential costs related to these personality traits that associate with higher fertility, they focused on health and conflicts. Neither, they discovered, really seemed to be an issue. If anything, they were consistently healthier. Which actually makes sense when you consider that of 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. The researchers found no evidence that intermediary levels of extroversion or other personality traits lead to highest fertility. Instead, greater levels of these traits associate with higher reproductive fitness, consistent with the evolutionary model referred to as directional selection.
But personality varied widely between the sexes — men scored higher on extroversion, agreableness, conscientiousness, openness, prosociality and industriousness. Indeed, the environment Tsimane face today may be somewhat novel. The annual growth rate of the Tsimane population over the last several decades is almost four percent —— meaning the population doubles every 17 years —— which suggests pioneer-like conditions. Greater market access, schooling and other opportunities are producing further changes in Tsimane society.
Skip to main content. Among Tsimane men, bold and outgoing personalities are associated with greater numbers of children.
For women? Not so much. By Andrea Estrada. Wednesday, October 23, - Santa Barbara, CA. JPG A Tsimane mother and her children share a meal. Download Image.
Their findings appear online in the journal Evolution and Human Behavior. Categories Alumni. International Affairs. It is in this push and pull of wanting to know more while still wanting to maintain mystery that the study of personality lies. And for this reason and many others , the science of personality has been woefully understudied and underappreciated. Among the primary challenges is that "personality" is extremely hard to define in a measurable way. With respect to an individual's personality, the Oxford dictionary defines it as " the combination of characteristics or qualities that form an individual's distinctive character ".
The Merriam-Webster dictionary defines it as " the complex of characteristics that distinguishes an individual or a nation or group; especially: the totality of an individual's behavioral and emotional characteristics ". How in the heck is one to measure "an individual's distinctive character" or "the totality of an individual's behavioral and emotional characteristics"?!
Evolutionary Developmental Theory
The task of developing a measurable definition for personality is less daunting when we consider the elements of it that we can agree upon: Personality involves: 1 differences in behavior across a population and 2 relative consistency of a type of behavior within an individual across time and in different contexts. Now if you pick a behavior you can measure, you can scientifically explore this one aspect of personality. Each of these could be measured on a sliding scale and in countless ways, providing information on both how populations vary and how consistent each individual is across multiple contexts for a given personality trait.
Psychologists have been studying human personality for a long time. The question as to whether other animals also have personalities is loaded with ethical implications, although anyone with a pet will tell you the answer is obvious. This framework makes the study of personality accessible to animal behaviorists, ecologists, and evolutionary biologists. And this isn't just a breakthrough for some of our most whimsical curiosities "Let's see exactly how social Fido is" , but it could provide us with important understandings of what makes some animals more adaptable to change, what neurological processes promote or restrain certain aspects of personalities, and how personalities evolve in response to their environments.
However, researchers expanding these personality concepts across species would have to be extra-cautious to avoid anthropomorphism the attribution of human characteristics to something non-human without scientific evidence. The study of the ecology and evolution of personalities is young, but there are already many interesting examples of where it can take us. One of the first was a landmark study by Felicity Huntingford in on anti-predator behavior, exploratory behavior and aggressiveness in three-spined sticklebacks.
Although she never used the words "personality" or "temperament", she showed that individual fish differed consistently in aggressiveness measures across multiple behavioral tests.
Evolutionary Personality Theories
She argues that this link between aggression towards your same species as well as towards predator species could serve an adaptive function, as both can be threats to offspring. A series of studies on rhesus macaques by Markku Linnoila and his colleagues found that males that were more aggressive, less socially affiliative, more impulsive, more prone to taking risks, and had higher mortality rates also had lower levels of the neurotransmitter serotonin.
Not only could these correlated personality traits be traced to a similar physiological attribute, but serotonin levels have a heritable component that can be influenced by evolutionary pressures. However, it's important to remember that personality traits are not necessarily permanent: They can change with context and experience.
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In a study of shyness-boldness of the Southern dumpling squid, David Sinn, Natalie Moltschaniwskyj, Erik Wapstra and Sasha Dall found that squid were bolder when feeding competition was higher and when they were larger. However, an individual that was bold in a feeding test was not necessarily bold in a threat test. Personality may seem like an enigma, but the study of personality could move us forward in important goals relating to conservation, mental health, evolutionary prediction, and genetics. But it will absolutely give us more to think about when we ponder "Who am I?
Integrating animal temperament within ecology and evolution, Biological Reviews, 82, DOI: Huntingford, F. The Relationship between anti-predator behavior and aggression among conspecifics in the three-spined stickleback, Gasterosteus aculeatus, Animal Behaviour, 24, Sinn, D. Are behavioral syndromes invariant?
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