Only engineering is capable of analyzing the nature of a machine in terms of the successful working of the whole; physics and chemistry determine the material conditions necessary for this success, but cannot express the notion of purpose. Similarly, only physiology can analyze the nature of an organism in terms of organs' roles in the body' s healthy functioning. Physics and chemistry cannot ascertain by themselves any of these operational principles. Which one of the following is an assumption required by the analogy? ['The functioning of the human organism is machine-like in nature.', 'Physiology as a science is largely independent of physics and chemistry.', 'Biological processes are irreducible to mechanical or chemical processes.', 'The notion of purpose used by engineers to judge the success of machinery has an analog in organisms.']