We don’t have to agree with James Lovelock’s call for a Moses to take us to the Arctic and preserve civilization. He is, in fact, an interesting and original scientist. When he first described Earth as a self-regulating system, the Gaia Hypothesis, the idea was dismissed and ridiculed. Now it is widely accepted, at least in its modern version. Daisyworld is a neat model of the hypothesis, try out a web-based simulation here.
James Lovelock is in the tradition of other great, original scientists who worked on self-regulating feedback systems. Here are six of the most interesting, four of them with a background in medicine. There are of course many others that could have been included (e.g. Herbert Simon). Lynn Margulis also worked with James Lovelock. She is, of course, best known for her work on the role of symbiosis in cell evolution.
Claude Bernard (1813-1873). Established the scientific method in medicine. Discovered self-regulating systems in the body. Wrote An Introduction to the Study of Experimental Medicine (1865).
Arturo Rosenblueth (1900-1970). Physician and collaborator with Walter Cannon and Norbert Wiener.
Norbert Wiener (1894-1964). Cybernetics, or Control and Communication in the Animal and Machine (1948). See Wikipedia entry on cybernetics.