11/24/2014 05:46 EST | Updated 01/24/2015 05:59 EST

How Similar Are Humans to Chimpanzees and Orangutans?

Do nonhuman primates (such as chimpanzees and orangutans) have personalities? And how similar are these personality to humans who share an evolutionary history with them?

Research looking at personality in humans has identified what is known as the Five-Factor Model of Personality with five broad personality factors describing personality. These factors (also known as the Big Five personality traits) are: openness to experience, conscientiousness, extraversion, , agreeableness, and neuroticism which appear to underlie the rich variety of ways that humans differ from one another. The Five Factor Model has inspired countless research studies as well as psychometric personality measures commonly used in psychology today. It also highlights the role of biological factors in shaping how personality grows and develops as we become more mature.

While research into the Five-Factor Model has shown that personality traits change over time, identifying personality changes in nonhuman primates has always been difficult. Since nonhumans are not capable of speech, measuring personality usually involves careful observation of how they interact with other nonprimates using a rating system. Based on behaviour ratings, different personality traits that appear equivalent to the Big Five Factors seen in humans have been identified in nonhuman primates as well. While some researchers remain skeptical about using behaviour ratings to measure personality in nonhumans, numerous research studies have shown intriguing similarities between humans and nonhumans in how personality changes develop across the lifespan.

Research using behaviour ratings on 202 chimpanzees has identified specific personality traits equivalent to the Big Five factors in humans as well as a personality trait specific to chimpanzees which the researchers called Dominance. These personality factors appear to change as chimpanzees grow older and also vary between males and females as well as whether the chimpanzees are in captivity or in the wild. In many ways, chimpanzees (who happen to be our closest living nonhuman relatives) appear to show a pattern of personality development that is very similar to what is seen in humans.

But how do chimpanzees compare to other non-human primate species that are not as social, such as orangutans? A new research study published in the Journal of Personality and Social Psychology compared personality differences between chimpanzees and orangutans to determine how closely they resembled human personality. Written by Alexander Weiss of the University of Edinburgh and James E. King of the University of Arizona, the study examined 174 and 202 chimpanzees living in zoos across North America, Australia, and Singapore. Since the chimpanzees and orangutans ranged in age from less than one year to more than fifty years, the experimenters were able to rate them across their entire lifespan as well as checking for sex differences in personality.

What Weiss and King found was that personality traits in chimpanzees do appear to change over time much as they do with humans. As with humans, chimpanzees appear to become more introverted, more agreeable, and less impulsive over time. Orangutans, on the other hand, aren't as social as chimpanzees and more likely to be aggressive and impulsive. There were also strong sex differences for chimpanzees with females being less aggressive and friendlier than males. Male chimpanzees are also more likely to cooperate with other males to fight outsiders while orangutans are more solitary. Sex differences were also stronger in chimpanzees than in orangutans or humans. Overall however, personality shifts across the lifespan appear remarkably similar for humans, chimpanzees, and orangutans.

So, what do these study findings actually suggest about human personality? Seeing similar personality trends in other species that have a shared evolutionary history with humans provides strong evidence that biology plays an important role in personality, perhaps even more than social or cultural influences. These results also suggest that sex differences in personality evolved independently in different species. Still, the relationship between heredity and environment is extremely complicated and more research needs to be done to explore how personality can be measured in different species.

Despite the problems involved in measuring personality in nonhuman species, studies such as this one help demonstrate how much of our personality is shaped by the evolutionary history that we share with nonhuman primates.


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