(1970) proposed a quantitative relationship between response rate (B) and reinforcement rate (Rf): B = k Rf / (Rf0 + Rf) where k and Rf0 are constants. Herrnstein proposed that this formula, which he derived from the matching law he had observed in studies of concurrent schedules of reinforcement, should be regarded as a quantification of the law of effect. While the qualitative law of effect may be a tautology, this quantitative version is not. Example An example is often portrayed in drug addiction. When a person uses a substance for the first time and receives a positive outcome, they are likely to repeat the behavior due to the reinforcing consequence. Over time, the person's nervous system will also develop a tolerance to the drug. Thus only by increasing dosage of the drug will provide the same satisfaction, making it dangerous for the user. Thorndike's Law of Effect can be compared to Darwin's theory of natural selection in which successful organisms are more likely to prosper and survive to pass on their genes to the next generation, while the weaker, unsuccessful organisms are gradually replaced and "stamped out". It can be said that the environment selects the "fittest" behavior for a situation, stamping out any unsuccessful behaviors, in the same way it selects the "fittest" individuals of a species. In an experiment that Thorndike conducted, he placed a hungry cat inside a "puzzle box", where the animal could only escape and reach the food once it could operate the latch of the door. At first the cats would scratch and claw in order to find a way out, then by chance / accident, the cat would activate the latch to open the door. On successive trials, the behaviour of the animal would become more habitual, to a point where the animal would operate without hesitation. The occurrence of the favourable outcome, reaching the food source, only strengthens the response that it produces. Colwill and Rescorla for example made all rats complete the goal of getting food pellets and liquid sucrose in consistent sessions on identical variable-interval schedules. Influence The law of work for psychologist B. F. Skinner almost half a century later on the principles of operant conditioning, "a learning process by which the effect, or consequence, of a response influences the future rate of production of that response." Skinner would later use an updated version of Thorndike's puzzle box,