Human beings are one of only a handful of "prosocial" animals — meaning we volunteer to help or share with others, even when there might not directly be any benefit to ourselves. Primates are also prosocial, and experimental studies have shown that rats and jackdaws might be, too. Now, thanks to a study out of the University of Veterinary Medicine in Vienna, researchers believe we should be including dogs on that list.

In the study, researchers conducted a test "in which the dogs had to pull trays and decide whether a second dog would retrieve a treat or not":

In the test, the donor dogs used their mouths to pull a string to bring a tray toward a second dog. They could choose either an empty tray or a tray containing a treat on the partner's side […] At the end of each test run, the researchers conducted another test to show that the donor dogs knew what pulling the tray meant. They allowed the donor dogs to pull on a tray to give themselves a treat, and all dogs did just that. [Science Daily]

Once researchers had controlled for dogs who were just pulling the string for fun, they found that "dogs truly behave prosocially toward other dogs," especially when they were familiar with the other dog beforehand. "What we also found was that the degree of familiarity among the dogs further influenced this behavior. Prosocial behavior was exhibited less frequently toward unfamiliar dogs than toward familiar ones," study director Friederike Range said.

In other words, dogs will willingly give treats to their friends — even when there is no direct reward for them. Jeva Lange