The Expression of the Emotions in Man and Animals

Chapter 1 endnote 3, from How Emotions are Made: The Secret Life of the Brain by Lisa Feldman Barrett.
Some context is:

A primary inspiration for this idea is Charles Darwin’s book 'The Expression of the Emotions in Man and Animals,' where he claimed that emotions and their expressions were an ancient part of universal human nature.

The Expression of the Emotions in Man and Animals, by Charles Darwin, isn’t as widely known as his masterwork, On The Origin of Species, but it’s had tremendous influence in psychology. Darwin wrote that facial movements like smiles and scowls are universal expressions of emotion and that they are found in non-human animals, illustrating that humans and other animals are descended from a common ancestor.

Darwin may have written Expression to provide evidence that for his ideas that humans and non-human animals shared a common ancestor, because this idea was very controversial when it was introduced in the 19th century.