" Science likes to measure things, to test hypotheses and collect data. Until quite recently science wasn’t testing hypotheses about animal feelings. From the time Charles Darwin wrote his last book, The Expression of the Emotions in Man and Animals (1872) to about the time Neil Armstrong left footprints on the moon nearly a century later (1969), prevailing scientific dogma denied animals their hearts and minds. A nonhuman animal was viewed as merely a responder to external stimuli. The idea that a walrus made decisions, or that a parakeet felt emotions, was considered unscientific. "

― Jonathan Balcombe , Second Nature: The Inner Lives of Animals