The idea of the club arose from a symposium on animal behaviour held by the Society of Experimental Biology in Cambridge, July 1949. The club was founded by the neurologist John Bates and continued to meet until 1958.
The name Ratio was suggested by Albert Uttley, it being the Latin root meaning "computation or the faculty of mind which calculates, plans and reasons". He pointed out that it is also the root of rationarium, meaning a statistical account, and ratiocinatius, meaning argumentative. The use was probably inspired by an earlier suggestion by Donald Mackay of the MR club, from Machina ratiocinatrix, a term used by Norbert Wiener in the introduction to his then recently published book Cybernetics, or Control and Communication in the Animal and the Machine. Weiner used the term in reference to calculus ratiocinator, a calculating machine constructed by Leibniz.
The initial membership was William Ross Ashby, Horace Barlow, John Bates, George Dawson, Thomas Gold, W. E. Hick, Victor Little, Donald MacKay, Turner McLardy, P. A. Merton, John Pringle, Harold Shipton, Donald Sholl, Eliot Slater, Albert Uttley, W. Grey Walter and John Westcott. Alan Turing joined after the first meeting with I.J. Good, Philip Woodward and William Rushton added soon after.
The club was the most intellectually powerful and influential cybernetics grouping in the UK, and many of its members went on to become extremely prominent scientists.