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The field of psychology has been greatly influenced by the study of genetics. Decades of research has demonstrated that both genetic and environmental factors play a role in a variety of behaviors in humans and animals (e.g. Grigorenko & Sternberg, 2003). The genetic basis of aggression, however, remains poorly understood. Aggression is a multi-dimensional concept, but it can be generally defined as behavior that inflicts pain or harm on another. Genetic-developmental theory states that individual differences in a continuous phenotype result from the action of a large number of genes, each exerting an effect that works with environmental factors to produce the trait. This type of trait is influenced by multiple factors making it more complex and difficult to study than a simple Mendelian trait (one gene for one phenotype). ==History== Past thought on genetic factors influencing aggression tended to seek answers from chromosomal abnormalities. Specifically, four decades ago, the XYY genotype was (erroneously) believed by many to be correlated with aggression. In 1965 and 1966, researchers at the MRC Clinical & Population Cytogenetics Research Unit led by Dr. Court Brown at Western General Hospital in Edinburgh reported finding a much higher than expected nine XYY men (2.9%) averaging almost 6 ft. tall in a survey of 314 patients at the State Hospital for Scotland; seven of the nine XYY patients were mentally retarded. In their initial reports published before examining the XYY patients, the researchers suggested they might have been hospitalized because of aggressive behavior. When the XYY patients were examined, the researchers found their assumptions of aggressive behavior were incorrect. Unfortunately, many science and medicine textbooks quickly and uncritically incorporated the initial, incorrect assumptions about XYY and aggression—including psychology textbooks on aggression. The XYY genotype first gained wide notoriety in 1968 when it was raised as a part of a defense in two murder trials in Australia and France. In the United States, five attempts to use the XYY genotype as a defense were unsuccessful—in only one case in 1969 was it allowed to go to a jury—which rejected it. Results from several decades of long-term follow-up of scores of unselected XYY males identified in eight international newborn chromosome screening studies in the 1960s and 1970s have replaced pioneering but biased studies from the 1960s (that used only institutionalized XYY men), as the basis for current understanding of the XYY genotype and established that XYY males are characterized by increased height but are not characterized by aggressive behavior. Though the link currently between genetics and aggression has turned to an aspect of genetics different from chromosomal abnormalities, it is important to understand where the research started and the direction it is moving towards today. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Genetics of aggression」の詳細全文を読む スポンサード リンク
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