Pigs, like humans, make decisions based on their mood and personalities, a group of British scientists has found.
"This finding demonstrates that humans are not unique in combining longer-term personality biases with shorter-term mood biases in judging stimuli," the researchers wrote in an article in Biology Letters, a scientific journal published by the British national science academy.
The study involved 36 pigs with personalities that were labelled "proactive" or "reactive", and housed in either an "enriched" environment or less pleasant living space. The pigs were trained to feed from bowls that would either yield a reward in the form of sugar-coated chocolate or an undesirable outcome in the form of coffee beans.
The research team then introduced a third bowl to see whether certain pigs were optimists or pessimists about the possibility of finding more treats in the new bowl.
The researchers found that proactive pigs were likely to respond with optimism regardless of their living conditions, but reactive pigs whose environment contributed to a good mood were much more likely to be optimistic than those whose living conditions were poorer.
The study's lead author, Dr Lucy Asher, said in a press release: "Our results suggest that judgement in pigs, and potentially in other animals, is similar to humans - incorporating aspects of stable personality traits and more transient mood states."