Because an individual''s fitness is determined by his performance relative to that of intraspecifics, an individual can increase fitness by improving his own performance or by inhibiting the performance of other individuals. The amount of adaptive value due solely to inhibiting others was investigated. The fitness of inhibitors is increased only to the degree to which they reduce the average performance of all noninhibitors in the population, not by the degree to which they reduce the performance of the specific individuals they actually inhibit. The adaptiveness of inhibition is directly proportional to the fraction of noninhibitors that is affected. The adaptive value of inhibitory traits is frequency dependent and is lowest when the trait is rare. Even if inhibition is done at no cost to the inhibitor, the adaptive value of inhibiting is probably so low when the trait 1st appears in large populations that selection would in many (most?) cases be too weak to keep the trait from being lost by drift. The cost of inhibiting must be infinitesimally small if selection in large populations is to favor inhibition, even if the losses suffered by individuals that are inhibited are much greater than the cost the inhibitor pays for his inhibition. Even if inhibitory traits become common in a population, the situation is always unstable because individuals that develop resistance to inhibition, but do not themselves practice inhibition always have a higher fitness than inhibitors. A model based on the superterritory concept suggests that inhibition of other individuals has limited significance in the evolution of territoriality. If inhibitory traits exist, natural selection may on occasion favor traits that worsen a species'' competitive ability and that even result in a species'' extinction. Inhibitory traits evolve most easily in specific situations, and predictions concerning the occurrence of such traits are made. Inhibition is more effective in maintaining traits at high frequencies than in causing rare traits to increase in frequency. Inhibitory traits probably have limited evolutionary importance. Selection nearly always favors channeling time and energy into improving an individual''s own performance rather than harming others, although inhibition via secretion of toxic substances may be a major exception.