Behavior

Behavior or behaviour (see American and British spelling differences) refers to the actions of a system or organism, usually in relation to its environment, which includes the other systems or organisms around as well as the physical environment. It is the response of the system or organism to various stimuli or inputs, whether internal or external, conscious or subconscious, overt or covert, and voluntary or involuntary.

Biology
In humans, behavior is believed to be controlled primarily by the endocrine system and the nervous system. It is most commonly believed that complexity in the behavior of an organism is correlated to the complexity of its nervous system. Generally, organisms with more complex nervous systems have a greater capacity to learn new responses and thus adjust their behavior.

Behaviors can be either innate or learned. However, current research in the Human Microbiome Project points towards a possibility that human behavior may be controlled by the composition of the microbe population within a human body.

More generally, behavior can be regarded as any action of an organism that changes its relationship to its environment. Behavior provides outputs from the organism to the environment.

Psychology
Human behavior (and that of other organisms and mechanisms) can be common, unusual, acceptable, or unacceptable. Humans evaluate the acceptability of behavior using social norms and regulate behavior by means of social control. In sociology, behavior is considered as having no meaning, being not directed at other people and thus is the most basic human action, although it can play a part in diagnosis of disorders such as the autism spectrum disorders. Animal behavior is studied in comparative psychology, ethology, behavioral ecology and sociobiology. According to moral values, human behavior may also depend upon the common, usual, unusual, acceptable or unacceptable behavior of others.

Behavior became an important construct in early 20th century psychology with the advent of the paradigm known subsequently as "behaviorism." Behaviorism was a reaction against "faculty" psychology which purported to see into or understand the mind without the benefit of scientific testing. Behaviorism insisted on working only with what can be seen or manipulated and in the early views of John B. Watson, a founder of the field, nothing was inferred as to the nature of the entity that produced the behavior. Subsequent modifications of Watson's perspective and that of "classical conditioning" (see under Ivan Pavlov) led to the rise of operant conditioning or "radical behaviorism," a theory advocated by B.F. Skinner, which took over the academic establishment up through the 1950s and was synonymous with "behaviorism" for many.

For studies on behavior, ethograms are used.

Other fields
Behavior outside of psychology includes physical property and chemical reactions.

Computer science
Behavior as used in computer science is an anthropomorphic construct that assigns "life" to the activities carried out by a computer, computer application, or computer code in response to stimuli, such as user input. Also, "a behavior" is a reusable block of computer code or script that, when applied to an object, especially a graphical one, causes it to respond to user input in meaningful patterns or to operate independently. Also, behavior is a value that changes over time (one of the key concepts in functional reactive programming). The term can also be applied to some degree to functions in mathematics, referring to the anatomy of curves.

Earth sciences
In environmental modeling and especially in hydrology, a behavioral model means a model that is acceptably consistent with observed natural processes, i.e., that simulates well, for example, observed river discharge. It is a key concept of the so-called Generalized Likelihood Uncertainty Estimation (GLUE) methodology to quantify how uncertain environmental predictions are.