Charles Darwin believed that animals possess intelligence. In The Descent of Man, he dedicated a chapter to illustrating "that there is no fundamental difference between man and the higher mammals in their mental faculties" (p. 66), believing that the difference between human intelligence and animal intelligence is simply a matter of degree.
Dr. Irene Pepperberg would agree. Her groundbreaking, three-decade research on Alex, an African gray parrot, investigates animal thinking and mirrors earlier linguistic and cognitive work conducted on chimps and dolphins.
An Editorial Review on Amazon.com notes that when Dr. Pepperberg began her research, no one believed birds had the potential for "language, consciousness, or anything remotely comparable to human intelligence" (http://www.amazon.com/Alex-Me-Scientist-Discovered-Intelligence/dp/0061672475/ref=pd_bbs_sr_1?ie=UTF8&s=books&qid=1226735266&sr=8-1).
Parrots have small brains, about the size of a shelled walnut, but Alex learned to differentiate concepts like bigger or smaller, could count to 8, and could identify colors. He could even express emotions, being jealous, for example, when Dr. Pepperberg paid attention to others. Apparently, he also loved to dance, and play the occasional joke.
Dr. Pepperberg appeared on NPR this past Wednesday. Here is the link to her interview, which includes details on how she taught language to Alex:
Alex died in 2007, and Dr. Pepperberg penned Alex and Me: How a Scientist and a Parrot Discovered a Hidden World of Animal Intelligence-and Formed a Deep Bond in the Process
as a tribute and good-bye to a parrot with whom she shared a close bond. Alex's last words to her were "You be good. I love you."
Check out some of the data on PBS.org, where neurobiologist Erich Jarvis reports that "[f]ully 75 percent of the brains of parrots, hummingbirds, and thousands of other species of songbirds is actually made up of a sophisticated information processing system that works much the same way as the locus of human higher-mindedness, the cerebral cortex..."