Behavior

What is behavior? A dictionary definition reveals that behavior consists of our activities and actions, especially actions toward one another. As such definitions suggest, many behavioral terms have meaning only in social comparisons: We identify others as contentious, courteous, or conscientious only by their actions in social contexts. A long-standing question in science and in everyday affairs inquires about the causes of individual differences in behavior: Why are some people gregarious extroverts and others timid, shy introverts?

Behavior genetics is a hybrid area of science, at the intersection of human genetics and psychology. Its focus is on how genes and environments contribute to differences in behavior. It is a young discipline. A book that gave the field its name was published in 1960, and a decade later the Behavior Genetics Association was founded. For a time, most behavior genetics research was an effort to show that the term was not itself an oxymoron—that variations in genes do contribute to individual differences in behavior. Now, as a result of that research, the relevance and importance of genetic variation to individual differences in behavior are widely accepted, and the challenging task is to identify specific gene-behavior pathways. In this entry, we will review the methods used to identify such pathways and then focus on one set of behaviors, use and abuse of alcohol, as a model for the study of genetic and environmental influences.

Twin and Adoption Studies

To determine whether variation in some dimension of behavior is heritable (whether behavioral differences are, in some part, due to genetic differences between people), human researchers use family, twin, and adoption designs. The first step in determining whether a behavior is influenced by genes is to establish that it aggregates or "runs" in families. Similarities in behavioral characteristics among family members suggest that genes influence the trait, but they cannot conclusively demonstrate genetic influence, because family members share their experiences (i.e., their environments) as well as their genes.

Twin and adoption studies allow one to tease apart the effects of genes and environments. Twin studies compare the patterns of behavioral characteristics between identical, or monozygotic (MZ), and fraternal, or dizygotic (DZ), twins. MZ twins share 100 percent of their genetic information, whereas DZ twins share, on average, one-half, just like non-twin siblings. Thus, the presence of greater behavioral similarities between MZ twins than DZ twins suggests that genetic factors contribute to those behaviors.

Adoption studies compare whether an adopted child is more similar behaviorally to the child's adoptive parents (with whom environments, but not genes, are shared) or to the child's biological parents (with whom genes, but not environments, are shared). Twin and adoption techniques have been used to demonstrate that nearly all behavior is under some degree of genetic influence, and, in the context of the Human Genome Project, behavior genetics has attracted great interest and some controversy.

Complex Genetics

New techniques allow behavior geneticists to ask not just whether a behavior is under genetic influence, but also what specific genes are involved. To identify genes involved in behavior, investigators use genetic markers—stretches of DNA that differ among individuals. One can either use genetic markers that are evenly spaced on all chromosomes, to search for genes influencing the behavior that are located anywhere in the genome (called genomic screening), or one can test markers at a specific gene believed to be, on theoretical grounds, involved in the behavior (called the candidate gene approach).

The idea behind these analyses is that if a particular gene is involved in the behavior, then people who are more alike with respect to the behavior will be more likely to share the same stretch of DNA that is at or near the gene. The difficulty in searching for genes involved in behavior is that there is no one-to-one correspondence between carrying a particular gene and exhibiting a particular behavior. There are no genes for behavior; there are only genes that influence behavior. Any particular behavior is a complex trait that involves more than one gene and is influenced by the environment as well.

For example, having a particular gene may make a person more likely to have problems with alcohol, but it does not determine whether or not the person will be an alcoholic. Some individuals will carry genes predisposing them to alcohol abuse but will never exhibit any problems, because they choose to abstain from alcohol. Other individuals will exhibit obvious alcohol problems, but will not carry the particular genes known to be involved.

This is because a large number of genes are risk-relevant for use and abuse of alcohol, and each has only a very small effect. Different genes may be acting in different individuals. And genes interact with each other and with the environment. Thus, individual outcomes result from a complex and ill-understood mixture of both genetic and environmental risk factors. That very complexity creates the diverse nature of human behavior. Indeed, it is what makes us uniquely human, but it also makes finding genes involved in human behavior extraordinarily difficult.

Animal Models

Because of this complexity, some investigators use animal models to complement human studies. Like humans, mice and rats differ in a variety of behavioral characteristics, including levels of alcohol use and tolerance or sensitivity to its effects. Animal studies allow breeding strategies that cannot be performed in humans. One approach that is commonly used in animal studies takes advantage of natural variation in behavior. Different strains of mice differ not only in coat color but also in preference for alcohol.

Under one of the most commonly used breeding strategies, animals from each of the behaviorally different mouse lines are allowed to mate with each other. Assuming the parents from each strain have different versions of genes contributing to alcohol use, subsequent generations of offspring will have different combinations of the genes contributing to the alcohol use and will display wide variation in their alcohol use. Such samples can be used to perform genetic studies searching for genes involved in the behavior, much like those described in humans: Animals more alike in their drinking behavior should be more likely to have inherited common stretches of DNA involved in the behavior.

One advantage of using animals is that the factors contributing to alcohol use in mice and rats are thought to be much simpler than the processes contributing to abuse in humans. Another is that animals' experience with alcohol can be experimentally controlled. Other strategies that are used in animals include inducing mutations or "knocking out " particular genes and studying the resultant aberrant behavior. If altering a particular gene consistently causes an alteration in a given behavior, the gene is likely involved in that behavior.

Alcoholism in Humans

The techniques available for human research are more limited, and many questions remain. Although behavior geneticists now possess the techniques to identify genetic influence and to begin to identify specific genes, questions remain regarding which behaviors, actions, and activities of people are the best candidates for behavior-genetic study.

Again, alcohol use and abuse provide an illustration. Alcoholism is a major social and medical problem in the United States and in most of the world. It is estimated that 10 percent of men and 4 percent of women in the United States experience alcohol dependency, at a cost of billions of dollars and 100,000 lives annually. Because use of alcohol is typically part of social interactions, familial (and possibly genetic) factors would be expected to contribute to variation in drinking.

But where shall we begin its study? Perhaps with diagnosed alcoholism? Most adults in our society use alcohol, yet only a fraction of them ever experience clinical symptoms of alcoholism. Perhaps we should begin much earlier, studying the decision to begin drinking? Obviously, one cannot become alcoholic without initiating drinking and then drinking large quantities regularly and with high frequency. Or perhaps much earlier yet, for behavioral predictors of alcoholism can be identified years before alcohol is first consumed.

Such predictors are apparent in early childhood, in behaviors evident to the children's parents, teachers, and peers. Long-term (i.e., longitudinal) studies conducted in several countries suggest that, as early as kindergarten and elementary school, behavioral ratings made by parents, teachers, or classmates distinguish children who are more likely to abuse alcohol later, in adolescence and early adulthood. Children who were impulsive, exploratory, excitable, curious, and distractible—and those who were less cautious, less fearful, less shy, and less inhibited—have a much greater risk of adult alcoholism than do children without those characteristics.

Twin studies have demonstrated that additive genetic variance, as well as familial-environmental influences, significantly contributes to the childhood behaviors that play a central role in the development of alcoholism risk. So, to understand the development of alcoholism, one must appreciate the complex developmental influences that affect children years before they first consume alcohol. Those influences reflect the interactions of dispositional differences in children's behavior with variations in their familial, social, and school environments.

Twin Studies of Alcoholism

That risk-related behaviors are evident early in life, remain stable into adolescence, and are associated with a family history of alcoholism suggests that those behaviors are, at least in part, of genetic origin. To establish that, researchers must use genetically informative study designs.

One approach is to study child or adolescent twins and their parents. Several such studies, which specifically assess the initiation of alcohol use and the transition to alcohol abuse, are being conducted throughout the world. We illustrate with two ongoing studies from Finland.

One, "FinnTwin12," is a study of approximately 2,800 twin pairs and their parents. The twins represent all pairs from five consecutive twin-birth cohorts (1983-1987) who were entered into the study as they reached age twelve (1995-1999), when behavioral ratings by teachers and parents were obtained on all participating pairs.

The ratings include multidimensional scales (i.e., scales that rate various characteristics) of behaviors associated with increased alcoholism risk. Two years later, at age fourteen, the twins were followed up, and, while most reported abstinence, about one-third were then using alcohol.

What predicts drinking or abstaining at age fourteen? Genetic factors played a role only among twin sisters, perhaps reflecting their more accelerated pubertal maturation, and environmental effects shared by twin siblings accounted for most of the variation in drinking or abstaining at this age. Differences that twins attributed to their home environments (e.g., in parental monitoring, support, and understanding) and differences in teachers' ratings of twins' behavior at age twelve (in problem behaviors of aggressiveness, impulsivity, and inattention) differentiated those who were drinking from those still abstaining at fourteen.

But once drinking is initiated, genetic effects become evident in individual differences in frequency and quantity of consumption and in behavioral problems that then result. "FinnTwin16," another study of five consecutive, complete birth cohorts of Finnish twins, illustrates. These twins were first studied as they reached age 16, with follow-up twelve and thirty months later, at ages 17 and 18^1/2. At age 16, about 25 percent had remained abstinent.

Of 2,810 twin pairs, both twins in 459 pairs (16.3%) were abstaining, co-twins in 1,964 pairs (69.9%) had concordantly begun drinking by age sixteen, and only 387 pairs were discordant, with one twin drinking and the other abstaining. Concordance is the co-occurrence of the behavior in the twin pair (e.g., both drinking or both not drinking). Overall concordance exceeded 85 percent, regardless of the twins' gender or zygosity.

There was extremely high familial aggregation for alcohol use or abstinence at age sixteen, additional evidence that genes play little role in abstinence or initiation. But thirty months later, individual abstinence had dropped to 10 percent, concordance among twin pairs had declined considerably, and genetic factors increasingly influenced the frequency and quantity of an adolescent's alcohol consumption. MZ twins were significantly more similar in drinking frequency than were DZ twins. The influence of genetic factors increases over time, with increasing experience with alcohol, and the differences between MZ and DZ twins becomes greater at each follow-up.

Regional residency moderates parental and sibling influences on adolescent drinking. Where abstinence is relatively rare, as in the large cities of Finland, siblings have greater effects on one another. Conversely, the protective effect of parental abstinence on that of their adolescent twin children was more evident in sparsely populated rural areas of the country, where abstinence was more prevalent. And, most interestingly, genetic factors exerted a larger role in urban settings than in rural settings from age 16 through the follow-up at age 18^1/2. Common environmental factors assumed greater importance in rural settings.

Such results suggest that environments moderate the impact of genetic effects across many dimensions of behavior. But what aspects of the environment matter? In an analysis of results at age 18^1/2, we demonstrated that specific characteristics of rural and urban environments moderate the effects of genes on drinking behavior. In areas with proportionately more young adults, genetic effects were nearly five times more evident than in communities with relatively few young adults. Thus, dramatic differences in the magnitude of genetic effects can be demonstrated across communities at environmental extremes of specific risk-relevant characteristics.

Complex Behaviors, Complex Causes

Thus, for use and abuse of alcohol, we know that the importance of genetic and environmental effects changes with sequencing in the use and abuse of alcohol, from abstinence or initiation to frequency of regular consumption, to problems associated with consumption, and ultimately, to diagnosed alcoholism and end-organ damage from the cumulative effects of alcohol. Similar stories could be told for many other behaviors of interest. Thus, for the major psychopathologies, from depression and schizophrenia in adults to attention deficit disorder in children or eating disorders in adolescents, genetic influences are invariably part of the story but never the whole story.

Genetic effects are always probabilistic and not deterministic. And the action of genes on behavioral outcomes is likely to be indirect. So we conclude with the same message with which we began: There are no genes for behavior, but behavioral development always represents an exquisite interplay between genes and environments. Gene-behavior correlations are modest and nonspecific; they alter risk but rarely determine outcome. Genes represent dispositions, not destinies.

Richard J. Rose

and Danielle M. Dick

Bibliography

Dick, Danielle M., and Richard J. Rose. "Behavior Genetics: What's New? What's Next?" Current Directions in Psychological Science 11 (2002): 70-74.

Rose, Richard J. "A Developmental Behavior-Genetic Perspective on Alcoholism Risk." Alcohol Health and Research World 22 (1998): 131-143.

Rose, Richard J., et al. "Drinking or Abstaining at Age 14? A Genetic Epidemiological Study." Alcoholism: Clinical and Experimental Research 25 (2001): 1594-1604.

Behavior

Animal behavior includes the actions and reactions of animals to external stimuli. The study of animal behavior involves two main approaches: answering questions about how an animal does something (proximate questions) and why an animal does something (ultimate questions). Though humans have always observed animals behave, animal behavior did not become a field of study until the 1930s, when it was called ethology .

Behavior is determined by both genetics and environmental factors, and is controlled by neural mechanisms. Thus, all animals with nervous systems are capable of behavior, including extremely simple ones such as the flatworm, Caenorhabditis elegans, which responds to light. The study of animal behavior is expanding rapidly and includes taxa and subjects too numerous to list here. Major divisions of the field include learning, cognition, and social behavior.

Founders of animal behavior studies include scientists Karl von Frisch, Konrad Lorenz, and Niko Tinbergen, whose work in the 1930s won them a shared Nobel Prize in 1973. Their work focused on how animals can do things they have never before seen done, which is a proximate question relating to the genetics that determine some of an animal's makeup and the physiology that allows the animal to perform the feat.

Their work also included elements of ultimate questions, and it is the answers to these "why" questions that lead us to fully understand the driving force behind the evolution of the behavior. Using the C. elegans example given above, questions about how the flatworm avoids light will be answered by geneticists and physiologists studying light sensors and locomotion capabilities. Why the flatworm avoids light relates to things like evolution (its ancestors avoided light, and it increases an individual's fitness for survival to do so) and environment (predators can detect flatworms better in the light). These ultimate questions helped link the fairly new study of behavior to established disciplines of evolution and ecology , and gave birth to the field we know today as behavioral ecology.

Behavior is a phenotypic trait , and, as with other such traits, an individual's behavior is determined through both genetics and environment. There are few examples of a trait that is strictly determined through just one of these routes, though through rigorous study we can tease apart the genetic and environmental components that determine a behavior.

For example, when a gene for a complex behavior such as alcoholism is reported, it usually means that there has been an abnormal allele of a gene found in some large percentage of alcoholics tested, and that the presence of this allele may somehow make the individuals with it more likely to be alcoholics. It does not indicate, however, that all people with that allele are alcoholics or that all alcoholics have that allele. There are many social factors such as depression and stress that contribute to alcoholism.

Behavior is controlled by the nervous system. Nerve cells acquire sensory cues from the environment, such as light in the case of C. elegans, and convert them to electrical signals that are transported to a central decision-making location, such as a nerve ganglion in C. elegans or the brain in a higher animal. There it will be determined whether the received stimulus demands a reaction. From there, another electrical signal will be sent back out to the target where the response will occur, such as a muscle that controls locomotion and performs the actual behavior.

Learning

One loosely defined category of animal behavior is learning, and this includes imprinting, kin recognition, associative learning, and play. During learning, behaviors are changed based on what an individual sees or experiences.

Imprinting is irreversible learning that occurs during a specific time in an individual's development. Documented in both mammals and birds, one type of imprinting is the recognition and bond that develops between the parent and child in the first few days after birth. A famous example of this occurred when Konrad Lorenz divided a clutch of goose eggs in half, and allowed half of them to incubate with their mother and the other half in an incubation chamber. Those in the first half displayed normal behavior, following their mother around and ultimately interacting and mating with other geese. Those in the second half spent their first few hours with Lorenz and the baby geese imprinted on him. Even when these geese were later reintroduced to their mother and siblings, they showed no recognition but instead always followed Lorenz around and even later showed courtship behavior toward humans. This experiment shows the importance of the critical period in which imprinting occurs (the first few hours of life in this case) and the irreversibility of what is learned, even when the species that is imprinted (a human in this case) is incorrect.

Another example of imprinting includes recognition of kin. At an early age, odors of the nest and early companions are used as cues that let animals recognize who their kin are. Documented even in insects, this kin recognition can be used to explain interactions later in life (significantly after separation from the nest) in which an animal treats another one like a relative if it smells like the nest from which it originated. This may be an important part of kin selection, which is discussed in the final, social behavior paragraph of this entry.

Other types of learning, such as associative learning, are not dependent on a critical period, though the learning may happen most efficiently if taught at a certain time. Associative learning is simply the ability to associate one stimulus with another. One example is trial-and-error learning, where as a result of a certain behavior and its outcome, a good or bad association is learned. Whether an association is positive or negative ultimately leads to the repetition or avoidance of the behavior. Food choices may fall under this category, where the sampling of different food types may lead to satisfaction and nourishment or bad taste and sickness.

Finally, play can be viewed as a type of learning in which capturing prey and social behavior are practiced. Though play is usually done with siblings and without the actual goals of hunting to kill or establishing social and mating hierarchies, the actions practiced in play allow these skills to be practiced for use later on.

Cognitive Behaviors

A second group of behaviors that can be loosely gathered together are cognitive behaviors. These are complex behaviors that involve the perception, storing, processing, and use of information.

Long-distance travel is an example of this complex process. Whales, butterflies, and birds travel thousands of kilometers to return to the exact same spot they were the year before. Migrating animals use several mechanisms including orientation, piloting, and navigation. Orientation involves moving in a certain compass direction, which can be known from cues like stars and the Sun, although some animals can detect magnetic north without these cues.

Piloting is employed for short distances. It involves moving between landmarks such as rivers and mountains that are familiar from past migrations.

Navigation is the most complex. It involves both determining present location in relation to other known locations and using orientation to get to the next destination. This means the animal must create a mental map that is spatially correct in order to plot out the next course.

Social Behaviors

A third group of behaviors is related to social living. Examples include communication, cooperation, and competition. Communication can be between species, such as when a dog snarls to expose its teeth to warn a potential attacker what may be in store. Frequently, communication occurs among species and can be aural such as bird song or cricket chirp; olfactory , such as a spot where an animal urinates; visual; or tactile .

Communication serves a myriad of purposes, including defining territories, attracting mates, telling where a food source is, or warning of impending danger. Cooperation is when two or more individuals work to perform a single task. Many times this task may seem more beneficial to one individual than the other, in which case the individual getting less or no benefit is termed altruistic. Examples of cooperation are in food finding, child rearing, and standing watch for predators.

In many cases of apparent altruism, it is found that the individual receiving the benefit is related to the one giving, such that the one giving is actually helping to preserve a genetically related line. This phenomenon is called kin selection and serves to propagate related genomes , an act that is not purely altruistic.

Competition occurs when a limited resource needs to be divided among individuals. An example of a resource to be divided is territory. Frequently, males must establish a territory that has good food or is a good mating or nesting spot so that they are preferentially chosen by females for mating. Those males who accomplish this are the most successful in passing on their genes. Competition for territory can take the form of violent contests with other males, and even after the territory is won it may need vigilant guarding to keep intruders out.

see also Acoustic Signals; Behavioral Ecology; Communication; Courtship; Social Animals; Sociobiology.

Jean K. Krejca

Bibliography

Alcock, John. Animal Behavior, 6th ed. Sunderland, MA: Sinauer Associates, 1998.

Campbell, Neil A., Jane B. Reece, and Lawrence G. Mitchell. Biology, 5th ed. Menlo Park, CA: Benjamin Cummings, 1999.

Halliday, Tim. Animal Behavior. Norman: University of Oklahoma Press, 1994.

Lorenz, Konrad. King Solomon's Ring. New York: Harper & Row, 1952.

Maier, Richard A., and Barbara M. Maier. Comparative Animal Behavior. Belmont, CA: Brooks/Cole Publishing, 1970.

Mellgren, Roger L., ed. Animal Cognition and Behavior. New York: North-Holland Publishing Company, 1983.

Wilson, Edward O. Sociobiology: The New Synthesis. Cambridge, MA: The Belknap Press of Harvard University Press, 1975.

Behavior

Behavior is the way that all organisms or living things respond to stimuli in their environment. Stimuli include chemicals, heat, light, touch, and gravity. For example, plants respond with growth behavior when light strikes their leaves. Behavior can be categorized as either instinctive (present in a living thing from birth) or learned (resulting from experience). The distinction between the two is often unclear, however, since learned behavior often includes instinctive elements. Plants and animals that lack a well-developed nervous system rely on instinctive behavior. Higherdeveloped animals use both instinctive and learned behavior. Generally, behavior helps organisms survive.

Plant behavior

The instinctive behavior of a plant depends mainly on growth or movement in a given direction due to changes in its environment. The growth or movement of a plant toward or away from an external stimulus is known as tropism. Positive tropism is growth toward a stimulus, while negative tropism is growth away from a stimulus. Tropisms are labeled according to the stimulus involved, such as phototropism (light) and gravitropism (gravity). Plants growing toward the direction of light exhibit positive phototropism. Since roots grow downward (with gravity),

Words to Know

Ethology: The scientific study of animal behavior under natural conditions.

Operant conditioning: Trial-and-error learning in which a random behavior is rewarded and subsequently retained.

Stimulus: Something that causes a behavioral response.

Tropism: The growth or movement of a plant toward or away from a stimulus.

they exhibit positive gravitropism. Stems of plants grow upward (against gravity), exhibiting negative gravitropism.

Animal behavior

The scientific study of animal behavior under natural conditions, known as ethology, focuses on both instinctual and learned behavior. Ethologists look at an animal's environment to see how events in that environment combine with an animal's instincts to shape overall behavior. This is especially important in the developing or early stages of an animal's life.

Animals exhibit various levels of instinctual behavior. On a elementary level are reflexes. A reflex is a simple, inborn, automatic response of a part of the body to a stimulus. Reflexes help animals respond quickly to a stimulus, thus protecting them from harm. Other instinctual behaviors are more complex. Examples of this kind include the nest-building behavior of birds and the dam-building behavior of beavers.

Imprinting. An example of animal behavior that combines instinct and learning is imprinting, often seen in birds such as geese and ducks. Within a short, genetically set time frame an animal learns to recognize and then bond to its parent, helping it to survive its infancy. Newly hatched geese or goslings are able to walk at birth. They quickly learn to recognize the movements of their parents and then follow them. If the parents are removed within the first few days after birth and are replaced by

any moving object, the goslings imprint or bond to that object, learning to follow it.

Animals often add to their set of instinctual behaviors through trial-and-error learning, known as operant conditioning. Young chimps, for example, watch their parents strip a twig and then use the prepared stick to pick up termites from rotten logs. When the young chimps repeat this procedure, their behavior is rewarded by the meal of termites, a preferred food. This reward teaches the chimps to repeat the same behavior when next hungry.

Courtship behaviors. There are many kinds of interactive behavior between animals. One of them is courtship behavior, which enables an animal to find, identify, attract, and arouse a mate. During courtship, animals use rituals, a series of behaviors performed the same way by all the males or females in a species. These include leaping and dancing, singing, the ruffling of feathers, or the puffing up of pouches. The male peacock displays his glorious plumage to the female. Humpback whales announce their presence under the sea by singing a song that can be heard hundreds of miles away.

Group behaviors. Some animals live together in groups and display social behavior. The group protects its members from predators, and allows cooperation and division of labor. Insects, such as bees, ants, and termites, live in complex groups in which some members find food, some defend the colony, and some tend to the offspring. Hierarchies or ranking systems help reduce fighting in a group. Chickens, for example, have a peck-order from the dominant to the most submissive. Each chicken knows its place in the peck-order and does not challenge chickens of higher rank, thereby reducing the chances of fighting. Interactions among group members get more complex with more intelligent species such as apes.

[See also Brain; Nervous system ]

be·hav·ior / biˈhāvyər/ (Brit. be·hav·iour) • n. the way in which one acts or conducts oneself, esp. toward others: good behavior his insulting behavior toward me. ∎  the way in which an animal or person acts in response to a particular situation or stimulus: the feeding behavior of predators. ∎  the way in which a natural phenomenon or a machine works or functions: the erratic behavior of the old car. PHRASES: be on one's best behavior behave well when being observed: warn them to be on their best behavior.

behavior in biology: see ethology .

behavior •Antakya •Britannia, lasagne •Katya • Vanya •Kenya, Mantegna, Sardegna, tenure •failure • Montagna •behaviour (US behavior), misbehaviour (US misbehavior), saviour (US savior) •seguidilla, tortilla •Monsignor •Melanesia, Micronesia, Polynesia •Tigrinya • De Falla • Vaisya •Lockyer • Bologna • sawyer • bowyer •alleluia, hallelujah •La Coruña •bunya, gunyah