Animals

Wild Chimp Personalities Remain Unchanged Over Time

Decades after Jane Goodall made the chimpanzees of Tanzania’s Gombe National Park famous, new studies validate her work on primate personalities.

Renowned primatologist Jane Goodall has spent much of her life studying chimpanzees at Gombe National Park in Tanzania and often remarks upon their distinct personalities. Over the years she observed easygoing mom Flo, macho Goblin, loner Fifi, and many more unique chimp characters.

Alexander Weiss of the University of Edinburgh was also drawn to Gombe, having taken his first trip to this verdant park in 2010. He fondly remembers watching an impressive and fearless high-ranking male, playful juveniles, and a chimpanzee in a patch of sunlight with a beatific look on its face.

“I spent a few days there and saw chimpanzees with a lot of different personalities,” Weiss told Seeker. “The range of behaviors and other characteristics exhibited was extensive and as clear, I thought, as those we see in other humans.”

Nevertheless, he said that Goodall and others have been told that personality in terms of non-human primates is best “swept under the carpet” when doing field research. 

Challenging that advice, Weiss and his team created a questionnaire on chimpanzee personality traits. It included the following descriptors: dominant, reckless, excitable, sociable, sensitive, sympathetic, innovative, active, helpful, inquisitive, impulsive, solitary, inventive, curious, decisive, stable, cool, individualistic, predictable, dependent/follower, thoughtfulness, vulnerable, conventional, and unemotional.

Eighteen field assistants at Gombe, many of whom have been observing chimpanzees for up to 35 years, rated the primates using the questionnaire starting in October 2010. Each assistant was charged with rating 21-43 of 128 chimps, so each was rated by 2-9 assistants The animals were from the Kasekela or Mitumba communities of chimpanzees at the park.

The results, published in the journal Scientific Data, were then compared to a similar rating of chimps within the Kasekela community. The prior study was conducted in 1973.

Both studies provide evidence for the existence of stable personality traits in chimpanzees. While individuals show slight variations over the years, such as being more or less excitable on a given day or week, overall patterns were clear.

The authors liken such patterns to stable traits observed in humans. For example, tall children grow over time, such that their rate of growth changes from year to year. They tend to grow into tall adults, however, so the basic descriptor of “tall” remains stable and can even predict later outcomes.

The 1973 chimp study made a fateful prediction about a primate. All of the raters noted that a female chimp named Passion had a “deviant” profile suggesting a more violent than usual nature.

Later, Passion and her daughter kidnapped and ate the infants of other chimps.

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Still other chimpanzees appear to exhibit incredible empathy toward others. In another recent study, Christine Webb of Columbia University, primatologist Frans de Waal, and their team observed chimps for eight years at the Yerkes National Primate Research Center.

Webb said she and her colleagues observed that many chimpanzees comfort others in distress consistently over their lifespan, which provided the first evidence of an empathetic personality.

There is now little doubt then that chimpanzees, like humans, have distinctive personalities that fall within a wide spectrum. Although parallels between the general traits of the two species exist, so do clear differences.

An earlier paper in the Journal of Research in Personality by James King and Aurelio José Figueredo of the University of Arizona found that both humans and chimps exhibit neuroticism, extraversion, openness to experience, agreeableness, and conscientiousness.

“However,” Weiss said, “there was another dimension, too, in chimpanzees, which combines aspects of assertiveness, competitive prowess, fearlessness, and other characteristics.”

Humans in their own ways can demonstrate those traits, but the characteristics tend to be more pervasive in chimps. King and Figueredo, however, concluded that there are “profound similarities in the personality structure of humans and chimpanzees.”

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The previous studies did not investigate the factors that contribute to personality. Other research, such as studies led by William Hopkins of Georgia State University, suggests that genetics are key.

In a study published in Current Biology, Hopkins and his team found that intelligence runs in chimp families.

“The suggestion here is that genes play a really important role in their performance on tasks while non-genetic factors didn’t seem to explain a lot,” Hopkins said.

Weiss agrees. “There is pretty good evidence that genes and biology contribute to at least some of the differences in personality that we see,” he said.  

The finding that personality traits remain stable over long periods of time would appear to strengthen that view. It is also possible that an individual’s personality tends to become more fixed at a certain age. For example, a dominant individual — chimp or human — who is used to getting his or her way may have trouble taking on a more subservient role later in life.

Studies on human twins and families over generations conclude that almost all traits are, at least in part, influenced by genetics.

For now, though, it remains unclear how much experience and environment affect primate personalities. If “deviant” Passion, for example, had gone through some kind of therapy, might she have acted less violently later in her life?

Weiss said too much speculation is required at this point to formulate a sufficient answer.

He and his team hope to better determine how personality traits are related to various outcomes.

“There's a huge amount of literature on human personality, which suggests that it influences multiple domains of our lives — everything from career performance, to relationships, to how long we live,” he said. “We're really interested in seeing if this is true for these personality measures in these chimpanzees, too.”

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Weiss hopes that others pay greater attention to personality in all animals, so that they can be viewed more as unique individuals rather than just as members of a particular species. This is especially true for chimpanzees, which are our closest living primate relatives.

Time is of the essence given that chimpanzee populations continue to decline. According to the International Union for Conservation of Nature, chimps are endangered, with only 170,000–300,000 estimated to still exist in the wild.

Weiss said chimpanzees "very likely" differ as much from one another as do we humans, and so losing chimpanzees would mean losing individuals and individuals yet to come.

Goodall has expressed similar sentiments over the years. She said in the 1996 documentary Jane Goodall’s Wild Chimpanzees, “It isn’t only human beings who have personality, who are capable of rational thought and emotions like joy and sorrow.”

This realization, she added, could help to resolve “many ethical problems [regarding how] we use and abuse animals.”

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