He who understands baboons would do more toward metaphysics than Locke.
In The Expression of the Emotions in Man and Animals (1872), Charles Darwin tacitly diminishes the difference between “man” and “animals” by matter-of-factly conflating, in passages fascinating and rich in detail, close examinations of human beings and “lower animals” (by which Darwin meant not relatively primitive animals but all “non-human” animals). Writing thirteen years after On the Origin of Species and one year after The Descent of Man, he takes as the object of his inquiry “the principle of the direct action of the excited nervous system on the body, independently of the will and in part of habit.” Not what might be self-described by people possessing language but rather what is displayed—“behavior.”
While most of Darwin’s text deals with emotions in man, in a number of chapters in The Expression of the Emotions the author takes pains to commingle species under such headings as “Serviceable Associated Habits,” “The Principle of Antithesis,” and “Action of the Nervous System.” Darwin’s implicit assumption is the likeness of man and “lower animals,” not their unlikeness. As man has a “voice,” so do animals have “voices”: “Cats use their voices much as a means of expression, and they utter, under various emotions and desires, at least six or seven different sounds.” The cat’s “purr of satisfaction…is one of the most curious.” A dog will make sounds resembling laughter, and “a bark of joy often follows a grin.” A consideration of man in agony or pain is naturally extended to other species in kindred situations:
There is said to be “gnashing of teeth” in hell; and I have plainly heard the grinding of the molar teeth of a cow which was suffering acutely from inflammation of the bowels. The female hippopotamus in the Zoological Gardens, when she produced her young, suffered greatly; she incessantly walked about, or rolled on her sides, opening and closing her jaws, and clattering her teeth together.
And so back to man again, whose eyes “stare wildly as in horrified astonishment” and whose body is covered in perspiration: “Hence the nostrils are generally dilated and often quiver; or the breath may be held until the blood stagnates in the purple face.”
Cattle, horses, dogs, cats, monkeys, birds—and man: all are subject to emotions, thus the “expression” of emotions of an involuntary, visceral nature. “With all or almost all animals, even with birds, Terror causes the body to tremble.” Wrinkling the face, furrowing the forehead, mating and fighting cries, cries of fury, erection of the hair, dilation of nostrils and of pupils of the eye, muscular contortions of the body—all cross the boundaries of species. Darwin presents a good deal of firsthand observation on the infants in his household of whom there were, over the years, ten of his own.
“Joy and affection” are attributed …