Foolishly wondering, even momentarily, if I might have thought of an original turn of phrase a Google search revealed the following:
Results 1 – 10 of about 280,000 for Descartes before de horse. (0.03 seconds)
The key to skepticism is to continuously and vigorously apply the methods of science to navigate the treacherous straits between “know nothing” skepticism and “anything goes” credulity. Over three centuries ago the French philosopher and skeptic, René Descartes, after one of the most thorough skeptical purges in intellectual history, concluded that he knew one thing for certain: Cogito ergo sum — I think therefore I am. But evolution may have designed us in the other direction. Humans evolved to be pattern-seeking, cause-inferring animals, shaped by nature to find meaningful relationships in the world. Those who were best at doing this left behind the most offspring. We are their descendents. In other words, to be human is to think:
Sum Ergo Cogito — I Am Therefore I Think.
(from http://www.skeptic.com )