In addition to being loyal, loving, and helpful, dogs can be very jealous . They even have a sense of justice , an Austrian study published today in the journal Proceedings of the National Academy of Sciences reveals.
Researcher Friederike Range and his colleagues tried to measure the behavior of the animals using well-trained dogs that quickly offer a paw when asked.
The scientists used pairs of dogs belonging to the same owner, but treated them differently: while one received a good reward when he lifted his leg (a sausage) the other was offered nothing. Upon detecting the "injustice" that was being committed, the aggrieved dog showed anger and resentment . And finally he stopped obeying the order.
"An essential element in the evolution of cooperation is sensitivity to the efforts of others compared to one's own costs and gains. Aversion to inequalities is a force that pushes or prevents us to cooperate," writes Range in PNAS .
Until now, the refusal to collaborate when witnessing unequal treatment of other companions had only been observed in primates. The new study with these companion animals reveals "an early stage in the evolution of cooperative behaviors that later appeared in apes and humans," a precursor to more complex human feelings such as envy .
