D: Yaël, we both know that one of the oldest conundrums for ancient natural philosophers was what exactly sets humans apart from other animals.

Y: And it’s still puzzling us today, Don. One common answer has been that humans are the only animals that think abstractly. That definition becomes less certain as we continue to learn more about the kinds of rational thought that other animals perform.

D: Of course, we’ve known for some time that animals can use tools, solve problems, and remember specific events. But we have also learned that many animals—elephants, lions, and ravens, for example—assess their goals to make decisions.

Y: Not only that: these animals and others make subjective estimates on how suitable an option is for them and even on how confident they are it will meet their goals. It turns out we aren’t alone in our capability for abstract thought, either.

D: In 2016, researchers determined that ravens can think about others’ minds. Ravens can predict when competitors may be watching them and spying on their food stores, planning to steal. In those cases, ravens will protect their stores against discovery even if they don’t see another bird. In essence, the raven makes decisions about their own behavior based on their perception of others.

Y: This is a complex social behavior that we no longer assume is exclusive to humans or our close primate relatives. In fact, matriarchal elephants in Kenya have shown that they can distinguish ethnicity, gender, and age in local tribespeople and are able to recognize which members of a tribe pose a threat. So, we move ever closer to understanding how animals are rational in unique ways.