From Natural History Magazine:
Pigs possess complex ethological traits similar to dogs and chimpanzees.
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Pigs’ ability to differentiate each other, part of what is termed social cognition, provides evidence that pigs are as socially complex as other intelligent mammals, including primates. This capacity forms the basis for all pig social relationships, including the establishment of dominance hierarchies. Dogs can discriminate between barks recorded in different contexts from the same individual, and also from different individuals in the same context. Elephants are well known for their sophisticated recognition of other individual elephants even over long distances. Pigs have the ability to discriminate between individuals, even closely-related individuals, by smell and by auditory cues, a finding that suggests pigs vocalize in ways unique to each individual. In one study, sows listening to the calls of piglets responded more strongly to the vocalizations of their own offspring than to unfamiliar piglets, suggesting pigs can tell each other apart by vocal cues alone.
Pigs can also differentiate between familiar and unfamiliar humans. This capacity to tell the difference between members of another species may indicate that pigs have significant cognitive flexibility. While dogs can tell individual humans apart and read some human facial expressions, pigs, who—unlike dogs—were not selectively bred for human companionship, can distinguish between humans by differences in body size and some facial aspects. In one study, young miniature pigs were handled gently and fed treats for five weeks. They were then put in a Y-shaped maze and were free to approach either the gentle, generous handler or an unfamiliar human. Results of the study showed that the pigs could tell the difference between the handler and the stranger by following a range of cues that relied on their senses of smell, sight, and hearing. Surprisingly, smell appeared to be the least useful sensory tool during this study.
More.
One wonders whether the fact that smell is the least used tool is due to humans’ tendency to smear chemicals on our bodies that are simply not an individual human smell. Much more of interest in the article.
Here is much more information and links about how animals think. Series coming soon.
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