Human behavior includes all patterns of behavior attributable to the human species as a whole and of individual people. It is studied by a range of natural and social sciences such as biology, neuroscience, psychology, anthropology and sociology. Human behavior is influenced by culture and tradition, as well as by human physiology and genetic factors. Collective human behavior is a separate subject of study, mostly concerned with population-scale phenomena such as evolutionary and emergent effects.
In their book The Material Life of Human Beings: Artifacts, Behavior and Communication, Andrea R. Miller and Michael Brian Schiffer provide two definitions of human behavior. First, behavior can be defined on a relational basis, as any activity of a person, involving the consequential manipulation of at least one "interactor", taken to mean a physical object in the person's environment or another person. This definition is appropriate for simple performance actions such as writing a letter or engaging in dialogue, but it leaves out complex or introspective human activities.
The second, broader definition is that human behavior consists of "all interactions in a given behavioral system." According to Miller and Schiffer such a broad definition of behavior is important because it unites various aspects of human actions, which have been studied in isolation in different fields. Thus, the primary focus of biologists on a range of reflexes and muscular motions as the basis of behavior and the main emphasis of sociologists on interpersonal relationships as its foundation can be united in one logical framework.
One of the most important scientific investigations with respect to human behavior focuses on identifying the primary factors that determine it. Recent findings in fields such as human genomics, cognitive and information sciences shed new light and improve our understanding of the ways, in which genes and learning influence behavior. What is more, investigations of complex social and ecological processes have revealed feedback mechanisms, in which collective human behavior itself may be responsible for changing the genetic makeup of the population over generations.
Such findings and the current state of the emerging field of behavioral genetics are summarized by the distinguished academics Cynthia Coll, Elaine Bearer and Richard Lerner, editors of the compendium Nature and Nurture: The Complex Interplay of Genetic and Environmental Influences on Human Behavior and Development.
The conclusion seems to be that there is no clear divide between the formative influences of genetic makeup and environmental influences on human behavior. Gene-environment interplay starts to affect the behavior and development of humans and animals from the embryonic phase and continues throughout their life experience. Expression of the genotype, or the coded programming of the human genes, is often flexible and very much affected by the environmental context. Heredity alone cannot explain behavioral or developmental differences among different groups of people.
There are instances where collective human behavior may have profound consequences, which are unintended on an individual level. Many major advances in human civilization are likely the result of what biophysicist Harold Morowitz calls "synergistic interactions" of individuals' actions. Thus, collective adaptive behavior such as settling may lead to a population-wide trend such as urbanization.
Similar processes, observed in physical as well as biological and social systems, are characterized by the emergence on a macro-level of unique characteristics or patterns that set the direction of the entire system. Morowitz claims that "emergent" behavioral phenomena have shaped the development of humankind from the early exclusion of other hominid species to the development of technology, agriculture, language and religion.