Pigs are social but only dogs are attached

Companion dogs' bond with their owners has long been described as special and unique. Indeed, from an ethological point of view, dogs’ bond with their owners can be defined as “attachment”, which is similar in function to that of a human mother with her infants.

In an attachment bond, the attached individual depends on the security-providing attachment figure.

Attachment has some well defined criteria: the attached individual should use the caregiver as a secure base when exploring a new environment, and as a “safe haven” in case of danger, and  display specific behaviors upon reunion with the caregiver after separation.

“Besides dogs, there are only a few  studies assessing if the behaviors of other companion animals fulfil the criteria of attachment,” explains Anna Gábor from the Neuroethology of Communication Lab at the ELTE Department of Ethology, first author of the study. “Therefore, whether human-analog attachment can arise in other domestic animals experiencing an intense socialization with humans, or, on the contrary, is facilitated by the artificial and unique selection for dependence to and cooperation with humans that dogs underwent during their domestication was still a question to answer.”

To address this question, the researchers compared the behaviors of young companion dogs with those of young companion pigs. “Like dogs, pigs are also group-living and extremely social animals, and when kept as companions, they have a similar role in human families to that of dogs” says Paula Pérez Fraga from the Neuroethology of Communication Lab at the ELTE Department of Ethology and co-first author of the study. “This is why they are a good model species for direct comparisons with companion dogs.”

The researchers tested the animals using the so-called “Strange Situation Test,” a validated behavioral test to assess  attachment behaviour. This test's basic feature is to expose the animal to separations from their owner  and encounters with a stranger. The premise is that if attachment behaviors emerge, there will be a clear distinct behavioral pattern toward the owner compared to the stranger in the relevant situations. The research team found that the “attachment behavioral pattern” towards the owner was present only in dogs, but not in pigs.

“This finding suggests that the domestication process and intense human socialization alone are not enough to trigger human-analog attachment behaviour to the human caregiver in animals,” explains Gábor.

“We argue that dogs were selected for dependency on and for working in intense cooperation with humans, which is a unique characteristic of dog domestication.”

This study was published on in Scientific Reports titled “Domestication and exposure to human social stimuli are not sufficient to trigger attachment to humans: a companion pig-dog comparative study”, written by Anna Gábor, Paula Pérez Fraga, Márta Gácsi, Linda Gerencsér and Attila Andics. This project was funded by the National Research, Development and Innovation Office, the Hungarian Academy of Sciences (Lendület Program), the Eötvos Loránd Research Network, the European Research Council (ERC) under the European Union's Horizon 2020 research and by Eötvös Loránd University (ELTE). 

Cover: Paula Pérez Fraga

Source: Institute of Biology