I feel, therefore I am

The sentence, "I feel, therefore I am," just popped into my head. I've been thinking again lately about what (if anything) can really be said to be "unique" to humans. In my mind, being the best at a lot of things (communication, tool use, problem solving, etc.) isn't nearly the same as being the only species to do something. Anyway, that's what got me headed down the path toward, "I feel, therefore I am." But, I wanted to see what the wider world thought of that phrase, so I googled it. That led me to a great article reviewing a book about the historic battle between Descartes and Spinoza, which Descartes won but looks like maybe shouldn't have... Hopefully I'll be able to check out the books Descartes' Error: Emotion, Reason, and the Human Brain, The Feeling of What Happens: Body and Emotion in the Making of Consciousness, and Looking for Spinoza: Joy, Sorrow, and the Feeling Brain some time.