"...swimming for hours with widely open mouth, thus catching, like a whale, insects in the water. Even in so extreme a case as this, if the supply of insects were constant, and if better adapted competitors did not already exist in the country, I can see no difficulty in a race of bears being rendered, by natural selection, more and more aquatic in their structure and habits, with larger and larger mouths, till a creature was produced as monstrous as a whale." -- Charles Darwin, On the Origin of Species by Means of Natural Selection (London: John Murray, 1859), 184.
In fairness, maybe he just meant that bears should be 40 to 60 feet tall due to "evolution"