Falling Sideways — Tom Holt

From the moment Homo Sapiens descended from the trees, possibly onto their heads, humanity has striven towards civilization. Fire. The Wheel. Running Away from furry things with more teeth than one might reasonably expect-all are testament to man's ultimate supremacy. It is a noble story and so, of course, complete and utter fiction. For one man has discovered the hideous truth: that humanity's ascent to civilization has been ruthlessly guided by a small gang of devious frogs. The man's name is David Perkins, and his theory is not, on the whole, widely admired, particularly not by the frogs themselves, who had invested a great deal of time and effort in keeping the whole thing quiet.