Editing Operant conditioning (section)

===Origins of operant behavior: operant variability===
Operant behavior is said to be "emitted"; that is, initially it is not elicited by any particular stimulus. Thus one may ask why it happens in the first place.  The answer to this question is like Darwin's answer to the question of the origin of a "new" bodily structure, namely, variation and selection. Similarly, the behavior of an individual varies from moment to moment, in such aspects as the specific motions involved, the amount of force applied, or the timing of the response. Variations that lead to reinforcement are strengthened, and if reinforcement is consistent, the behavior tends to remain stable. However, behavioral variability can itself be altered through the manipulation of certain variables.<ref>{{cite journal|last1=Neuringer|first1=A|year=2002|title=Operant variability: Evidence, functions, and theory|journal=Psychonomic Bulletin & Review|volume=9|issue=4|pages=672–705|doi=10.3758/bf03196324|pmid=12613672|doi-access=free}}</ref>