The idea that humans alone have the capacity for intelligence, self-awareness, and emotions has a long history. Early in the scientific revolution, René Descartes helped establish the perception of animals as stimulus-response machines, driven purely by instinct and lacking any capacity for reason. Generations of scientists have subsequently been influenced by this viewpoint, with only the occasional dissenter.

One of the contrarians was none other than Charles Darwin, who recognized the emotional similarities between humans and animals, noting that “the difference in mind between man and the higher animals, great as it is, certainly is one of degree and not of kind.” In 1872, he wrote an entire book on the subject (The Expression of the Emotions in Man and Animals). But despite Darwin’s scientific prominence, he failed to dislodge the prevailing viewpoint that emotions are the exclusive domain of humans.

In his latest book, Mama’s Last Hug...

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