Pigs Become Optimists or Pessimists for the Same Reasons Humans Do

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Photo: Liesel Conrad/Getty Images

Every decision you make is shaped to some degree by your “cognitive bias,” the combination of your mood and your personality, two elements — one fluctuating, one stable — that come together to influence how you think. And for the first time, scientists have demonstrated that this pattern extends beyond our species: A study published today in the journal Biology Letters found that pigs, too, can be optimists or pessimists, with their outlook depending on those same two things.

For the study, the authors tested the pigs’ personalities — specifically, whether they were more proactive (a trait that corresponds to extraversion) or reactive (which corresponds to neuroticism) — by putting them in a pen with an unfamiliar object, like a bucket or a traffic cone, and observing how they reacted to its presence. In a separate test, the researchers also nudged the pigs’ mood upward or downward by putting them in fancy pens, with “deep straw and a larger space allowance,” or in less luxurious accommodations. After they’d spent some time in their new digs, the pigs were let into a room with two bowls, one containing chocolates — a treat for pigs, too — and the other containing coffee beans, apparently a turnoff for porcine taste buds. Once the pigs got used to this setup, the researchers started adding other, empty bowls to the room to test the animals’ outlook — the optimists, hopeful that the new bowl also contained a treat, would investigate more quickly, while the pessimists, burned by the coffee beans, would take their time.

The Los Angeles Times summed up the results:

The scientists found that the pigs with proactive personalities tended to check out the middle bowl, even without the sure promise of a reward, regardless of the quality of their accommodations. Being stuck in the economy lodgings didn’t change their underlying optimism.

Pigs with reactive personalities, on the other hand, were more optimistic about their chances of finding a chocolate in the middle bowl if they’d had the deluxe accommodations — and more pessimistic if they’d been in the less comfortable pen. Reactive animals, then, were much more affected by their environment, and their mood likely skewed their choices.

“These results suggest that judgement in non-human animals is similar to humans,” the authors wrote, and “that humans are not unique in combining longer-term personality biases with shorter-term mood biases in judging stimuli.” The trough can be half-empty or half-full, and pigs, like us, use a combination of factors to decide which one is true.