elifesciences | In mammals, helping is preferentially provided to members of one’s own
group. Yet, it remains unclear how social experience shapes pro-social
motivation. We found that rats helped trapped strangers by releasing
them from a restrainer, just as they did cagemates. However, rats did
not help strangers of a different strain, unless previously housed with
the trapped rat. Moreover, pair-housing with one rat of a different
strain prompted rats to help strangers of that strain, evidence that
rats expand pro-social motivation from one individual to phenotypically
similar others. To test if genetic relatedness alone can motivate
helping, rats were fostered from birth with another strain and were not
exposed to their own strain. As adults, fostered rats helped strangers
of the fostering strain but not rats of their own strain. Thus, strain
familiarity, even to one’s own strain, is required for the expression of
pro-social behavior.
