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January 14, 2014
This photo shows an albino and black-hooded rat during empathy test. Credit:
University of Chicago, Kevin Jiang
Empathy-driven behavior has been observed in rats who will free trapped
companions from restrainers. This behavior also extends toward strangers, but
requires prior, positive social interactions with the type (strain) of the
unfamiliar individual, report scientists from the University of Chicago, in the
open access journal eLife on Jan. 14
The findings suggest that social experiences, not genetics or kin selection,
determine whether an individual will help
strangers out of empathy. The
importance of social experience extends even to rats of the same strain—a rat
fostered and raised with a strain different than itself will not help strangers
of its own kind.
"Pro-social behavior appears to be determined only by
social experience," said
Inbal Bartal, PhD, a post-doctoral fellow at the University of Chicago and lead
author of the study "It takes diverse social interactions during development or
adulthood to expand helping behavior to more groups of unfamiliar individuals.
Even in humans, studies have shown that exposure to diverse environments reduces
social bias and increases pro-social behavior."
In 2011, a team led by Bartal and Peggy Mason, PhD, professor of neurobiology at
the University of Chicago, discovered that rats exhibit empathy-like helping
behavior. They found that rats consistently freed companions that were trapped
inside clear restrainers, and this behavior was driven by a rat version of
To determine whether rats would behave similarly toward strangers, the
researchers worked with two rat strains, one albino and the other with a
black-hooded fur pattern. Free rats, which were always albino, were first tested
with trapped albino strangers they had never previously interacted with, even by
smell. They encountered a different stranger every day, once per day, for 12
days. Free rats quickly became consistent openers for these albino strangers.
When free albino rats were tested with a black-hooded stranger, however, the
majority did not open the restrainer for the trapped individual. By contrast,
albino rats who were housed with a black-hooded companion were observed to
consistently liberate their black-hooded cage-mates.
To see if a rat could be motivated to help a stranger of a different strain,
albino rats were housed for two weeks with a black-hooded rat, and then
re-housed with another albino rat before being tested with black-hooded
strangers. These rats, which had known only one black-hooded individual during
their lifetimes, freed trapped black-hooded strangers. These tests suggest that
rats do not need to be familiar with an individual to display empathy-driven
helping behavior, but that
they do need to be familiar with the strain of a rat.
Peggy Mason and Inbal Bartal of the University of Chicago describe how they
discovered that rats will help strangers out of empathy, but with a caveat --
they will only help rats of a type they are familiar with. Credit: University of
Chicago, Kevin Jiang
To determine if this strain familiarity is needed for a rat's own strain,
newborn albino rats were fostered with black-hooded mothers and littermates.
These albino rats were raised in an environment in which they were denied any
exposure to rats of their own strain. When tested, these
rats helped trapped black-hooded
strangers but not albino strangers.
"Rats are apparently able to categorize others into groups and modify their
social behavior according to group membership," Bartal said. "Genetic similarity
or relatedness to another individual really has no influence at all."
"Rats are not born with an innate identity or motivation to help their own
type," Mason said. "It's only through social interactions that they form bonds
that elicit empathy and motivate helping. There are no mirrors in nature, so
what they see forms their identity."
With these behavioral patterns established in an animal model, the researchers
are optimistic the underlying biological mechanisms of helping and group
categorization can be explored, and that these results can inform future studies
in other social species, including humans.
"Exposure to and interaction with different types of individuals motivates them
to act well toward others that may or may not look like them," added Mason. "I
think these results have a lot to say about human society."