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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