The debate about whether (and, if so, how) animals think is an ancient one. Aristotle considered it important enough to write on the question extensively, and it’s a safe bet people were debating it long before we have written records. Unsurprisingly, it’s a major topic of research today, but one that tends to defy easy answers.

A big part of the story of zoology over the last 60 years has been learning that we have been underestimating animals’ intelligence. In the 17th century, René Descartes alleged that animals were mere machines, incapable of sensations, let alone feelings or thoughts. This view is now so outdated that the debate is usually not about whether animals think, but how much, and whether this meets certain definitions.

For example, we’ve gone from defining humans by our t

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