A devotee of Locke would argue that the ducklings are just picking up simple traits—perhaps a smell, sound, color, or shape. But Kacelnik and his student Antone Martinho III showed that they can do more. The duo presented newborn ducklings with pairs of objects that were either identical or different in shape or color. And they found that the birds could learn these traits. They weren’t imprinting on a specific shape or color, but on the concepts of “same” or “different.” They were looking beyond the individual objects to think about how they are related. In short, “they were abstracting properties,” says Kacelnik.

“I’m very impressed with the results, and the fact that after so many studies on imprinting, nothing like this has been done before,” says Nathan Emery from Queen Mary University of London, who studies bird behavior and was not involved in the research. “I think this has got the potential to revolutionize our field and will be discussed for years to come.”

This is far from the first blow to the idea that abstract thought is a human-only skill. Researchers have shown that other primates, including chimps and monkeys, can discriminate collections of the same items from sets of different ones—a skill that has been described as “the keel and backbone of thought and reasoning.” Rats can tell same from different too, as apparently can pigeons, parrots, crows, and even bees.

But in almost all of these experiments, the animals were extensively trained. They saw many combinations of objects, which were variously paired with rewards, before being tested. Martinho and Kacelnik did nothing of the kind. They hatched mallard eggs in the dark and, within an hour, ushered the newborn ducklings straight into an experiment.

Put yourself in the ducklings’ shoes. You leave the dark and enter a white arena with a pair of hanging objects—a red cone and a red cylinder—revolving around the centre. You study them for 25 minutes before being herded back into the dark waiting room. When you reenter the arena, there are now two pairs of objects. In one corner, two pyramids revolve around each other. In the other, a cube goes round a cylinder. Neither pair exactly matches the one you saw before. But the cube and cylinder have a familiar property—they’re different from each other. So you waddle over to them.

Martinho and Kacelnik did this experiment with 76 ducklings. At first, they saw a pair of objects that were same or different, in either shape or color. Then, they gave them a choice between two fresh pairs—one same, the other different.

Around 68 percent of the young birds headed towards the relation that they had seen before. If they had imprinted on one identical pair of objects, they were more likely to prefer a second identical pair over a different one. But if they imprinted on mismatched objects, they preferred other mismatched pairs over identical ones. “Their brains are accumulating a catalog of properties that could apply to other objects,” says Kacelnik.