The predatory instincts of subhuman species, as displayed in primitive interspecies tendencies, are the death instinct in man. Simple destruction has no biological function, but man's destructive behavior toward his fellow man or toward himself is a derivative of the biological function of predation. Masochism and sadism are the result of the appropriation of those predatory drives by Eros. Regression facilitates the break-through of death instincts. Under normal conditions, in man and in subhuman species, intraspecies predation is inhibited; but the techniques of predation, such as pursuit and fighting, may occur in intraspecies erotic behavior.