Behavioral Genetics
Behavioral genetics is the science that applies genetic analysis to the study of behavior. Genetic analysis is a technique used to study the individual differences in the manifestation of a trait as a result of genetic architecture. An example is the nature-versus-nurture controversy with respect to intelligence: genetic analysis may be used to determine how much of a person's intelligence is determined by his genetic makeup.
Mental disorders like schizophrenia can be genetically analyzed using the method developed by Francis Galton of comparing the traits of identical twins that are reared in different environments. This method was applied by Franz Kallmann since the 1930s to the 1950s, concluding that schizophrenia is a disorder that is largely inherited. This result was confirmed by adoption studies made by Leonard Heston and David Rosenthal in the 1960s.
The study of genetic influence in human behavior by methods of this kind is difficult because of the ethical issues that are arisen. Rigorous experiments are sometimes unfeasible because families should be misinformed about the characteristics of the participants. Therefore, experimentation with animals is preferred and often conducted to determine if a behavior is genetically stimulated. Besides experimentation, a great amount of knowledge comes from natural cases of inborn metabolism and chromosomal alterations.
Behavioral genetics considers that the ability to express certain behavior depends upon the genetic architecture of the individual. For example, a bird defending its territory, or a child learning to speak, are availing themselves of neural and muscle tissues that developed because of the existence of genetic information in their bodies' cells. Exactly how specific genes control specific behaviors is still unknown. However, experiments made with animals by altering a single gene have shown that this is enough to make that, for example, a mouse change its locomotion pattern.
Although genes are influential in behavior, they are not by all means the only factor. Learning is also needed to the complete development of the animal as was proved by experiments in which young monkeys were deprived of social interaction. When adults, these animals manifested troubles in their capacity to show normal social behavior.
Evolution provides animals with physiological mechanisms to support certain behaviors. Specialized sensory neurons exist that react to stimuli that are important to instinctive behaviors like reproducing, feeding, or predator avoidance. For example, the noctuid moth has in its ears neurons that function as bat detectors. When they are activated by the ultrasonic cry of bats, signals are sent that stop wing activity and the animal drops steeply.
Higher order activities that are learned rather than instinctive, such as speaking a language, also take advantage of neural specialization. There exist in the human brain regions that store information about the sounds of the words, and others that help in structuring a grammatical phrase. The existence and location of these regions were determined as a result of accidental injury to the brain.
The manifestation of instinctive behaviors is in many occasions triggered by environmental circumstances. The migratory birds, for example, experiment a whole cycle of behavior that is controlled by hormonal releases. The increasing length of the day in the spring produces hormones that lead the animal to migrate. After the migration, other hormones cause the behaviors associated with courting, mating, and young feeding.
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