The first known comparison between organism and machine is usually attributed to the Greek physician Hippocrates, who likened the human body to a water clock. The latest technology in 400 bc, water clocks were hydraulic devices whose various parts were controlled by a carefully balanced flow of water in order to tell the time. The core of the analogy between organism and clock turns on the idea that organisms can be explained in terms of regular, recurring, automatically controlled events among their parts. It positions the body as a purely mechanical thing, which can only be understood by studying it as such. It is hard to overstate the importance of this idea to much of the scientific progress that has occurred since the 17th century. The machine analogy and the mechanistic approach to biology it inspired have brought with them undeniable success.