Dogs' Love Isn't Unconditional After All

In a gray, linoleum-floored laboratory in Vienna, two dogs sit in side-by-side enclosures. One dog pulls a handle, and a tray laden with sausage moves down to where the other dog can reach it and excitedly gulp it down. How many times the first dog does this—giving a gift to another, with no benefit to itself—is a measure of what cognition researchers call “prosociality,” or, in essence, generosity. Specifically, how many times it gives food to a friend, or a strange dog, or just offers it to an empty enclosure can help researchers understand whether prosociality exists in dogs, part of a larger quest to understand which creatures are capable of generosity and how and when the trait evolved.