By Emma Young
We’re all familiar with the “Big Five” model of personality, which measures the traits of conscientiousness, agreeableness, extraversion, neuroticism, and openness. But what drove the evolution of these personality domains? And how do animal personalities compare with ours? Answers to the second question can help to answer the first. And now a major new study of personality in bottlenose dolphins, published in the Journal of Comparative Psychology, has found that in some key ways, dolphin personality is like ours; in others, though, it is not.
The 134 dolphins studied by Blake Morton at the University of Hull and colleagues were all kept in captivity in 15 centres in eight different countries. Staff who had known the dolphins for at least a year rated each animal on a 49-item Dolphin Personality Questionnaire, adapted from a similar questionnaire for primates. Staff indicated the extent to which dolphins showed various traits, such as “exhibitionistic, flamboyant” (for dolphins who regularly try to attract visitors’ attention, say), “aggressive”, “sociable”, “erratic”, “playful”, “easygoing”, “suspicious”, and “stubborn”. Many of the dolphins were rated by two or more people, and the reasonable consistency between different people’s ratings for a single animal gave the team some confidence that these were accurate.
The team then analysed the data, and found that the traits clustered into four main groups, or domains: openness (a tendency to be active and explore the environment), disagreeableness (a tendency to be aggressive, jealous, despotic and obstinate), sociability (being friendly towards other dolphins and people), and “directedness”, characterised by consistency in behaviour, boldness, and low emotional arousal (this was like a blend of high conscientiousness and low neuroticism). In contrast to findings for chimpanzees or gorillas, a domain of “dominance” did not emerge. This domain is notably absent from human personality models, too, perhaps because neither dolphin nor human social groups feature very strong hierarchies, while chimp groups do, the team suggests.
As with orcas, California sea lions, mountain gorillas and bonobos, bottlenose dolphins don’t seem to have a domain of “neuroticism”, either. It’s been suggested that neuroticism is more likely to emerge in species that live in unpredictable environments (the theory is that neurotic individuals may be more prone to anxiety but also more vigilant when it comes to spotting dangers in their environment — and an unpredictable environment requires greater vigilance). But the data on dolphins, which, as the researchers note, evolved in relatively unpredictable environments, runs counter to this idea. The questionnaire didn’t include many neuroticism-related items, however. More work is now needed to explore the origins of neuroticism in other animals as well as us, the team observes.
It has been suggested that conscientiousness evolves in species that need to pay close attention to other individuals — to carefully watch another using a tool, and so learn how to use it, for example. Though dolphins do learn to use tools from other dolphins, the team did not find evidence that conscientiousness, in and of itself, is a clear domain of their personality. Something like human conscientiousness has been observed in Asian elephants, however. These elephants have highly manipulatable and useful trunks, which are similar in some ways to our hands. Perhaps, then, the need to pay close attention to the use of hands (or trunks) in manipulating objects and caring for infants is important for the evolution of conscientiousness, the team suggests.
What about the similarities between the personalities of dolphins and people, beyond the lack of a trait of dominance? Openness has been found in other intelligent species that also live in groups, such as chimpanzees, as well as humans (but not orangutans, which don’t live in stable social groups). The finding for dolphins fits with this pattern, and more work is now needed to explore the extent to which one or both of these two factors might have contributed to the evolution of this trait, the team writes. Agreeableness (or disagreeableness) is also shared, but as the traits that relate to sociability in dolphins are different to those seen in humans and other primates, more work is needed to explore this, too.
It will be fascinating simply to know more about other animals’ personalities, of course, but the team certainly also hopes that it will provide some broader insights into how our own human personality evolved: “Further work on cetaceans, other aquatic mammals and other vertebrates will lead to a better understanding of the evolutionary forces that unite and divide species that inhabit the surface and depths of our planet,” the team concludes.