1) Operant selection or the ontogenic analogue of phylogenic or Darwinian selection, expressed as an abbreviated form of the selection of behaviour by its consequences. In a more general sense, all varieties of selection involve consequences (e.g., the evolution of the eye depends on the consequences of more finely differentiated seeing). Phylogenic selection operates on populations of organisms over evolutionary time whereas operant selection operates on populations of responses within the lifetime of an individual organism. Cultural selection is a third kind of selection. It occurs when behaviour is passed on from one member of a group to another (examples include imitated behaviour and verbal behavior).

2) The causative principle for biology, behavior, and culture is selection by consequences. With regard to biology, mutation and sexual reproduction ensure a range of variation in genes that code for the features of organisms. Some physical attributes meet the requirements of the environment. Organisms with these adaptive features survive and reproduce, passing their genetic material to the next generation. Organisms without these characteristics do not survive as well and their genes are less represented in the subsequent population. Natural selection is therefore a form of selection by reproductive consequences that occurs at the biological level. (Pierce + Epling) Selection by consequences has been extended to the level of behavior. Operant behaviour is an expressed characteristic of many organisms, including humans. Organisms with an extensive range of operant behaviour adjust to new environmental situations on the basis of the consequences that follow behavior. This kind of selection occurs over the life of the individual. Operants are the physical units selected at the behavioural level. The process of the selection and change of operants is analogous to evolution and natural selection at the genetic level. Reinforcement is therefore an ontogenetic process that extends selection by consequences to the level of behavior. (Pierce + Epling) A third level of evolution and selection occurs at the cultural level. The physical unit of selection at this level is the cultural practice. A cultural practise involves the interlocking operant behaviour of many people. As with operants, cultural practises vary in form and frequency. Different ways of doing things are more or less successful in terms of efficiency, productivity, and survival of group members. Generally, cultural practises are selected by aggregate outcomes, increasing or decreasing the rate of adoption of the practice.