Genetics Influencing Aggression
Encyclopedia
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. Because this type of trait is influenced by multiple factors, it is more complex and difficult to study than a simple Mendelian trait (one gene
for one phenotype
).
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 8 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. Today the link between genetics and aggression has turned to a different aspect of genetics than chromosomal abnormalities but it is important to understand where the research started to understand the direction it is moving towards today.
, as well as other behavioral traits, is studied genetically based on its heritability
through generations. Heritability models of aggression are mainly based on animals due to the ethical concern in using humans for genetic
study. Animals are first selectively bred and then placed in a variety of environmental conditions, allowing researchers to examine the differences of selection
in the aggression of animals.
plays in the behavior
:
These three main experimental types are used in animal studies
, studies testing heritability and molecular genetics
, and gene interaction/environment studies. Recently, important links between aggression and genetics have been studied and the results are allowing scientists to better understand the connections.
of aggression has been observed in many animal strains after noting that some strains of birds, dogs, fish, and mice seem to be more aggressive
than other strains. Selective breeding
has demonstrated that it is possible to select for genes that lead to more aggressive behavior in animals. Selective breeding examples also allow researchers to understand the importance of developmental timing for genetic influences on aggressive behavior. A study done in 1983 (Cairns) produced both highly aggressive male and female strains of mice dependent on certain developmental periods to have this more aggressive behavior expressed. These mice were not observed to be more aggressive during the early and later stages of their lives but during certain periods of time (in their middle-age period) were more violent and aggressive in their attacks on other mice. Selective breeding is a quick way to select for specific traits with the effects of selection being seen within a few generations of breeding. These characteristics make selective breeding an important tool in the study of genetics and aggressive behavior.
are often used as a model for human genetic
behavior since mice and humans have homologous genes
coding for homologous proteins that are used for similar functions at some biological levels. Mice aggression studies have led to some interesting insight in human aggression. Using reverse genetics
, the DNA
of genes for the receptors of many neurotransmitter
s have been cloned and sequenced, and the role of neurotransmitters in rodent aggression has been investigated using pharmacological manipulations. Serotonin
has been identified in the offensive attack by male mice against intruder male mice. Mutants were made by manipulating a receptor for serotonin by deleting a gene for the serotonin receptor. While exhibiting normal behavior in everyday activities such as eating and exploration, these mutant male mice with the knockout alleles attacked intruders with twice the intensity of normal male mice. In offense aggression in mice, males with the same or similar genotype
s were more likely to fight than males that encountered males of other genotypes. Another interesting finding in mice dealt with mice reared alone. These mice showed a strong tendency to attack other male mice upon their first exposure to the other animals. The mice reared alone were not taught to be more aggressive; they simply exhibited the behavior. This implicates the natural tendency related to biological aggression in mice because the mice reared alone lacked a parent to show them when to be aggressive.
is influenced by genetics
, experiments designed to study biological mechanisms are utilized. Molecular genetics
studies allow many different types of behavioral traits to be examined by manipulating genes
and studying the effect of the manipulation.
studies have focused on manipulating candidate aggression genes
in mice and other animals to induce effects that can be possibly applied to humans. Most studies have focused on polymorphisms
of serotonin
receptors, dopamine
receptors, and neurotransmitter
metabolizing enzyme
s. Results of these studies have led to linkage analysis to map the serotonin-related genes and impulsive aggression. In particular, the serotonin 5-HT seems to be an influence in inter-male aggression
either directly or through other molecules that use the 5-HT pathway. 5-HT normally dampens aggression in animals and humans. Mice missing specific genes for 5-HT were observed to be more aggressive than normal mice and were more rapid and violent in their attacks. Other studies have been focused on neurotransmitters. Studies of a mutation
in the neurotransmitter metabolizing enzyme monoamine oxidase A (MAO-A) have been shown to cause a syndrome that includes violence and impulsivity in humans. Studies of the molecular genetics pathways are leading to the production of pharmaceuticals to fix the pathway problems and hopefully show an observed change in aggressive behavior.
A rare genetic variant causing MAO-A deficiency has been associated with violent behavior in males. In 2002 a study published by researchers at King's College London
found a link between a genetic variant causing low levels of MAO-A and increased levels of antisocial behavior in people who had been mistreated as children. An American group studying monkeys called MAO-A a "warrior gene" in 2004. A 2008 study found a similar result involving the variant of the MAO-A gene, as well as the genes DAT1 and DRD2. In all three cases, the variants of these genes were associated with an elevated risk of violent and delinquent behavior, but only in people who experienced certain stresses during childhood.
is related to genetic factors or environmental factors, twin studies and adoption studies are used. These studies examine correlations based on similarity of a trait and a person's genetic or environmental factors that could influece the trait. Aggression
has been examined via both twin studies and adoption studies.
, twin studies were almost the only mode of investigation of genetic
influences on personality. Heritability
was estimated as twice the difference between the correlation
for identical, or monozygotic, twins and that for fraternal, or dizygotic, twins. Early studies indicated that personality was fifty percent genetic. Current thinking holds that each individual picks and chooses from a range of stimuli
and events largely on the basis of his genotype
and creates a unique set of experiences, basically meaning that people create their own environments.
studies allow genetic factors of behavior to be tested by taking advantage of the fact that an adopted person shares their genetic
makeup with their biological parents but was actually raised by people other than the biological parents. Therefore, if a behavior is genetic the person should resemble their biological parent but if a behavior is more environmentally influenced, the person will resemble the parent that raised the person. One adoption study in Denmark found that adoptive siblings split into separate foster homes had a 12.9% concordance rate of crime and aggressive behavior. This study also showed correlations between biological parents who committed criminal activity and their children they gave up for adoption committing criminal activity. This seems to suggest that biological characteristics which increase the risk for criminal convictions and aggression are transmitted from biological parents to their offspring and increase risk for criminal convection. Though many believe that new technology is making twin and adoption studies seem less relevant they are still important in assessing the role of environmental factors versus genetic factors in such characteristics as aggression.
researchers are now using genetic information as a control variable in experiments allowing them to be better able to study the environmental affects on aggression. Current thinking is that eventually studies investigating the effectiveness of aggression prevention programs will test genotypes of participants and identify those who are at "more risk" towards aggression. These more at risk people will be compared to less at risk individuals to examine how well prevention programs can combat genetic aggression. For now it is safe to say that studies exploring the genetic factors of aggression will still be mostly confined to animal studies as the ethics of human studies is still a debate.
Many species of animals still need to be studied to better understand genetics of aggression. At the moment, studies on monkeys, fish, and small mammals are being conducted and will utilize genetic information and understanding to better understand the role the environment plays alongside genetics in the development of aggression. These comparative genetics studies will allow researchers to compare similar traits of aggression in many species and also identify special aggressive traits specific to certain animals all allowing for a better model of human aggression.
Psychology
Psychology is the study of the mind and behavior. Its immediate goal is to understand individuals and groups by both establishing general principles and researching specific cases. For many, the ultimate goal of psychology is to benefit society...
has been greatly influenced by the study of genetics
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
. 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
Aggression
In psychology, as well as other social and behavioral sciences, aggression refers to behavior between members of the same species that is intended to cause humiliation, pain, or harm. Ferguson and Beaver defined aggressive behavior as "Behavior which is intended to increase the social dominance of...
, 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
Phenotype
A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...
result from the action of a large number of genes
Gênes
Gênes is the name of a département of the First French Empire in present Italy, named after the city of Genoa. It was formed in 1805, when Napoleon Bonaparte occupied the Republic of Genoa. Its capital was Genoa, and it was divided in the arrondissements of Genoa, Bobbio, Novi Ligure, Tortona and...
, each exerting an effect that works with environmental factors to produce the trait. Because this type of trait is influenced by multiple factors, it is more complex and difficult to study than a simple Mendelian trait (one gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
for one phenotype
Phenotype
A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...
).
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 MRCMedical Research Council (UK)
The Medical Research Council is a publicly-funded agency responsible for co-ordinating and funding medical research in the United Kingdom. It is one of seven Research Councils in the UK and is answerable to, although politically independent from, the Department for Business, Innovation and Skills...
Clinical & Population Cytogenetics Research Unit led by Dr. Court Brown at Western General Hospital
Western General Hospital
The Western General Hospital , at Crewe Road, Edinburgh, Scotland is part of NHS Lothian, a Heath Board which provides a comprehensive range of adult and paediatric care to the people of Edinburgh, the Lothians and beyond.It is one of the main teaching hospitals affiliated to the University of...
in Edinburgh
Edinburgh
Edinburgh is the capital city of Scotland, the second largest city in Scotland, and the eighth most populous in the United Kingdom. The City of Edinburgh Council governs one of Scotland's 32 local government council areas. The council area includes urban Edinburgh and a rural area...
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
State Hospital for Scotland and Northern Ireland
The State Hospital for Scotland and Northern Ireland is a psychiatric hospital providing care and treatment in conditions of high security for around 140 patients from Scotland and Northern Ireland who need to be detained in hospital under conditions of special security that can only be provided...
for Scotland
Scotland
Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...
; 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
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
and France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
. In the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, 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 8 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. Today the link between genetics and aggression has turned to a different aspect of genetics than chromosomal abnormalities but it is important to understand where the research started to understand the direction it is moving towards today.
Heritability
AggressionAggression
In psychology, as well as other social and behavioral sciences, aggression refers to behavior between members of the same species that is intended to cause humiliation, pain, or harm. Ferguson and Beaver defined aggressive behavior as "Behavior which is intended to increase the social dominance of...
, as well as other behavioral traits, is studied genetically based on its heritability
Heritability
The Heritability of a population is the proportion of observable differences between individuals that is due to genetic differences. Factors including genetics, environment and random chance can all contribute to the variation between individuals in their observable characteristics...
through generations. Heritability models of aggression are mainly based on animals due to the ethical concern in using humans for genetic
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
study. Animals are first selectively bred and then placed in a variety of environmental conditions, allowing researchers to examine the differences of selection
Selection
In the context of evolution, certain traits or alleles of genes segregating within a population may be subject to selection. Under selection, individuals with advantageous or "adaptive" traits tend to be more successful than their peers reproductively—meaning they contribute more offspring to the...
in the aggression of animals.
Research methods
As with other topics in behavioral genetics, aggression is studied in three main experimental ways to help identify what role geneticsGenetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
plays in the behavior
Behavior
Behavior or behaviour refers to the actions and mannerisms made by organisms, systems, or artificial entities in conjunction with its environment, which includes the other systems or organisms around as well as the physical environment...
:
- HeritabilityHeritabilityThe Heritability of a population is the proportion of observable differences between individuals that is due to genetic differences. Factors including genetics, environment and random chance can all contribute to the variation between individuals in their observable characteristics...
studies – studies focused to determine whether a trait, such as aggression, is heritable and how it is inherited from parent to offspring. These studies make use of genetic linkage maps to identify genesGênesGênes is the name of a département of the First French Empire in present Italy, named after the city of Genoa. It was formed in 1805, when Napoleon Bonaparte occupied the Republic of Genoa. Its capital was Genoa, and it was divided in the arrondissements of Genoa, Bobbio, Novi Ligure, Tortona and...
associated with certain behaviors such as aggression. - Mechanism experiments – studies to determine the biological mechanisms that lead certain genes to influence types of behavior like aggression.
- Genetic behavior correlationCorrelationIn statistics, dependence refers to any statistical relationship between two random variables or two sets of data. Correlation refers to any of a broad class of statistical relationships involving dependence....
studies – studies that use scientific data and attempt to correlate it with actual human behavior. Examples include twin studies and adoptionAdoptionAdoption is a process whereby a person assumes the parenting for another and, in so doing, permanently transfers all rights and responsibilities from the original parent or parents...
studies.
These three main experimental types are used in animal studies
Animal studies
Animal studies is a recently recognized field in which animals are studied in a variety of cross-disciplinary ways. Scholars from fields as diverse as: art history, anthropology, biology, film studies, geography, history, psychology, literary studies, museology, philosophy, and sociology; and from...
, studies testing heritability and molecular genetics
Molecular genetics
Molecular genetics is the field of biology and genetics that studies the structure and function of genes at a molecular level. The field studies how the genes are transferred from generation to generation. Molecular genetics employs the methods of genetics and molecular biology...
, and gene interaction/environment studies. Recently, important links between aggression and genetics have been studied and the results are allowing scientists to better understand the connections.
Selective breeding
The heritabilityHeritability
The Heritability of a population is the proportion of observable differences between individuals that is due to genetic differences. Factors including genetics, environment and random chance can all contribute to the variation between individuals in their observable characteristics...
of aggression has been observed in many animal strains after noting that some strains of birds, dogs, fish, and mice seem to be more aggressive
Aggressive
“Aggressive” is a New York-based Grammy award-winning music video and commercial directing team of Alex Topaller and Daniel Shapiro.Aggressive has been described by Movie Creation Mag as “having a fascination with the wonderful, in the likes of the surrealist Rafal Olbinski” and “tenacious about...
than other strains. Selective breeding
Selective breeding
Selective breeding is the process of breeding plants and animals for particular genetic traits. Typically, strains that are selectively bred are domesticated, and the breeding is sometimes done by a professional breeder. Bred animals are known as breeds, while bred plants are known as varieties,...
has demonstrated that it is possible to select for genes that lead to more aggressive behavior in animals. Selective breeding examples also allow researchers to understand the importance of developmental timing for genetic influences on aggressive behavior. A study done in 1983 (Cairns) produced both highly aggressive male and female strains of mice dependent on certain developmental periods to have this more aggressive behavior expressed. These mice were not observed to be more aggressive during the early and later stages of their lives but during certain periods of time (in their middle-age period) were more violent and aggressive in their attacks on other mice. Selective breeding is a quick way to select for specific traits with the effects of selection being seen within a few generations of breeding. These characteristics make selective breeding an important tool in the study of genetics and aggressive behavior.
Mouse studies
MiceMICE
-Fiction:*Mice , alien species in The Hitchhiker's Guide to the Galaxy*The Mice -Acronyms:* "Meetings, Incentives, Conferencing, Exhibitions", facilities terminology for events...
are often used as a model for human genetic
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
behavior since mice and humans have homologous genes
Gênes
Gênes is the name of a département of the First French Empire in present Italy, named after the city of Genoa. It was formed in 1805, when Napoleon Bonaparte occupied the Republic of Genoa. Its capital was Genoa, and it was divided in the arrondissements of Genoa, Bobbio, Novi Ligure, Tortona and...
coding for homologous proteins that are used for similar functions at some biological levels. Mice aggression studies have led to some interesting insight in human aggression. Using reverse genetics
Reverse genetics
Reverse genetics is an approach to discovering the function of a gene by analyzing the phenotypic effects of specific gene sequences obtained by DNA sequencing. This investigative process proceeds in the opposite direction of so-called forward genetic screens of classical genetics...
, the DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
of genes for the receptors of many neurotransmitter
Neurotransmitter
Neurotransmitters are endogenous chemicals that transmit signals from a neuron to a target cell across a synapse. Neurotransmitters are packaged into synaptic vesicles clustered beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to...
s have been cloned and sequenced, and the role of neurotransmitters in rodent aggression has been investigated using pharmacological manipulations. Serotonin
Serotonin
Serotonin or 5-hydroxytryptamine is a monoamine neurotransmitter. Biochemically derived from tryptophan, serotonin is primarily found in the gastrointestinal tract, platelets, and in the central nervous system of animals including humans...
has been identified in the offensive attack by male mice against intruder male mice. Mutants were made by manipulating a receptor for serotonin by deleting a gene for the serotonin receptor. While exhibiting normal behavior in everyday activities such as eating and exploration, these mutant male mice with the knockout alleles attacked intruders with twice the intensity of normal male mice. In offense aggression in mice, males with the same or similar genotype
Genotype
The genotype is the genetic makeup of a cell, an organism, or an individual usually with reference to a specific character under consideration...
s were more likely to fight than males that encountered males of other genotypes. Another interesting finding in mice dealt with mice reared alone. These mice showed a strong tendency to attack other male mice upon their first exposure to the other animals. The mice reared alone were not taught to be more aggressive; they simply exhibited the behavior. This implicates the natural tendency related to biological aggression in mice because the mice reared alone lacked a parent to show them when to be aggressive.
Biological mechanisms
In exploring how aggressionAggression
In psychology, as well as other social and behavioral sciences, aggression refers to behavior between members of the same species that is intended to cause humiliation, pain, or harm. Ferguson and Beaver defined aggressive behavior as "Behavior which is intended to increase the social dominance of...
is influenced by genetics
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
, experiments designed to study biological mechanisms are utilized. Molecular genetics
Molecular genetics
Molecular genetics is the field of biology and genetics that studies the structure and function of genes at a molecular level. The field studies how the genes are transferred from generation to generation. Molecular genetics employs the methods of genetics and molecular biology...
studies allow many different types of behavioral traits to be examined by manipulating genes
Gênes
Gênes is the name of a département of the First French Empire in present Italy, named after the city of Genoa. It was formed in 1805, when Napoleon Bonaparte occupied the Republic of Genoa. Its capital was Genoa, and it was divided in the arrondissements of Genoa, Bobbio, Novi Ligure, Tortona and...
and studying the effect of the manipulation.
Molecular genetics
A number of molecular geneticsMolecular genetics
Molecular genetics is the field of biology and genetics that studies the structure and function of genes at a molecular level. The field studies how the genes are transferred from generation to generation. Molecular genetics employs the methods of genetics and molecular biology...
studies have focused on manipulating candidate aggression genes
Gênes
Gênes is the name of a département of the First French Empire in present Italy, named after the city of Genoa. It was formed in 1805, when Napoleon Bonaparte occupied the Republic of Genoa. Its capital was Genoa, and it was divided in the arrondissements of Genoa, Bobbio, Novi Ligure, Tortona and...
in mice and other animals to induce effects that can be possibly applied to humans. Most studies have focused on polymorphisms
Polymorphism (biology)
Polymorphism in biology occurs when two or more clearly different phenotypes exist in the same population of a species — in other words, the occurrence of more than one form or morph...
of serotonin
Serotonin
Serotonin or 5-hydroxytryptamine is a monoamine neurotransmitter. Biochemically derived from tryptophan, serotonin is primarily found in the gastrointestinal tract, platelets, and in the central nervous system of animals including humans...
receptors, dopamine
Dopamine
Dopamine is a catecholamine neurotransmitter present in a wide variety of animals, including both vertebrates and invertebrates. In the brain, this substituted phenethylamine functions as a neurotransmitter, activating the five known types of dopamine receptors—D1, D2, D3, D4, and D5—and their...
receptors, and neurotransmitter
Neurotransmitter
Neurotransmitters are endogenous chemicals that transmit signals from a neuron to a target cell across a synapse. Neurotransmitters are packaged into synaptic vesicles clustered beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to...
metabolizing enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
s. Results of these studies have led to linkage analysis to map the serotonin-related genes and impulsive aggression. In particular, the serotonin 5-HT seems to be an influence in inter-male aggression
Aggression
In psychology, as well as other social and behavioral sciences, aggression refers to behavior between members of the same species that is intended to cause humiliation, pain, or harm. Ferguson and Beaver defined aggressive behavior as "Behavior which is intended to increase the social dominance of...
either directly or through other molecules that use the 5-HT pathway. 5-HT normally dampens aggression in animals and humans. Mice missing specific genes for 5-HT were observed to be more aggressive than normal mice and were more rapid and violent in their attacks. Other studies have been focused on neurotransmitters. Studies of a mutation
Mutation
In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...
in the neurotransmitter metabolizing enzyme monoamine oxidase A (MAO-A) have been shown to cause a syndrome that includes violence and impulsivity in humans. Studies of the molecular genetics pathways are leading to the production of pharmaceuticals to fix the pathway problems and hopefully show an observed change in aggressive behavior.
A rare genetic variant causing MAO-A deficiency has been associated with violent behavior in males. In 2002 a study published by researchers at King's College London
King's College London
King's College London is a public research university located in London, United Kingdom and a constituent college of the federal University of London. King's has a claim to being the third oldest university in England, having been founded by King George IV and the Duke of Wellington in 1829, and...
found a link between a genetic variant causing low levels of MAO-A and increased levels of antisocial behavior in people who had been mistreated as children. An American group studying monkeys called MAO-A a "warrior gene" in 2004. A 2008 study found a similar result involving the variant of the MAO-A gene, as well as the genes DAT1 and DRD2. In all three cases, the variants of these genes were associated with an elevated risk of violent and delinquent behavior, but only in people who experienced certain stresses during childhood.
Human behavior genetics
In determining if a traitTrait
Trait may refer to:* Trait, a characteristic or property of some object* Trait , which involve genes and characteristics of organisms* Trait theory, an approach to the psychological study of personality...
is related to genetic factors or environmental factors, twin studies and adoption studies are used. These studies examine correlations based on similarity of a trait and a person's genetic or environmental factors that could influece the trait. Aggression
Aggression
In psychology, as well as other social and behavioral sciences, aggression refers to behavior between members of the same species that is intended to cause humiliation, pain, or harm. Ferguson and Beaver defined aggressive behavior as "Behavior which is intended to increase the social dominance of...
has been examined via both twin studies and adoption studies.
Twin studies
Twin studies manipulate the environmental factors of behavior by examining if identical twins raised apart are different from twins raised together. Before the advancement of molecular geneticsMolecular genetics
Molecular genetics is the field of biology and genetics that studies the structure and function of genes at a molecular level. The field studies how the genes are transferred from generation to generation. Molecular genetics employs the methods of genetics and molecular biology...
, twin studies were almost the only mode of investigation of genetic
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
influences on personality. Heritability
Heritability
The Heritability of a population is the proportion of observable differences between individuals that is due to genetic differences. Factors including genetics, environment and random chance can all contribute to the variation between individuals in their observable characteristics...
was estimated as twice the difference between the correlation
Correlation
In statistics, dependence refers to any statistical relationship between two random variables or two sets of data. Correlation refers to any of a broad class of statistical relationships involving dependence....
for identical, or monozygotic, twins and that for fraternal, or dizygotic, twins. Early studies indicated that personality was fifty percent genetic. Current thinking holds that each individual picks and chooses from a range of stimuli
Stimulus (physiology)
In physiology, a stimulus is a detectable change in the internal or external environment. The ability of an organism or organ to respond to external stimuli is called sensitivity....
and events largely on the basis of his genotype
Genotype
The genotype is the genetic makeup of a cell, an organism, or an individual usually with reference to a specific character under consideration...
and creates a unique set of experiences, basically meaning that people create their own environments.
Adoption studies
AdoptionAdoption
Adoption is a process whereby a person assumes the parenting for another and, in so doing, permanently transfers all rights and responsibilities from the original parent or parents...
studies allow genetic factors of behavior to be tested by taking advantage of the fact that an adopted person shares their genetic
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
makeup with their biological parents but was actually raised by people other than the biological parents. Therefore, if a behavior is genetic the person should resemble their biological parent but if a behavior is more environmentally influenced, the person will resemble the parent that raised the person. One adoption study in Denmark found that adoptive siblings split into separate foster homes had a 12.9% concordance rate of crime and aggressive behavior. This study also showed correlations between biological parents who committed criminal activity and their children they gave up for adoption committing criminal activity. This seems to suggest that biological characteristics which increase the risk for criminal convictions and aggression are transmitted from biological parents to their offspring and increase risk for criminal convection. Though many believe that new technology is making twin and adoption studies seem less relevant they are still important in assessing the role of environmental factors versus genetic factors in such characteristics as aggression.
Future research
The explosion of genetic discoveries and the thinking of a new generation of scientists and social scientists have allowed genetics and aggression to be linked together without as much controversy as was characteristic in the past. Much of the current research involving genetics and aggression is aimed at understanding the link between genes and the environment that leads to aggression. PsychosocialPsychosocial
For a concept to be psychosocial means it relates to one's psychological development in, and interaction with, a social environment. The individual needs not be fully aware of this relationship with his or her environment. It was first commonly used by psychologist Erik Erikson in his stages of...
researchers are now using genetic information as a control variable in experiments allowing them to be better able to study the environmental affects on aggression. Current thinking is that eventually studies investigating the effectiveness of aggression prevention programs will test genotypes of participants and identify those who are at "more risk" towards aggression. These more at risk people will be compared to less at risk individuals to examine how well prevention programs can combat genetic aggression. For now it is safe to say that studies exploring the genetic factors of aggression will still be mostly confined to animal studies as the ethics of human studies is still a debate.
Many species of animals still need to be studied to better understand genetics of aggression. At the moment, studies on monkeys, fish, and small mammals are being conducted and will utilize genetic information and understanding to better understand the role the environment plays alongside genetics in the development of aggression. These comparative genetics studies will allow researchers to compare similar traits of aggression in many species and also identify special aggressive traits specific to certain animals all allowing for a better model of human aggression.
See also
- AggressionAggressionIn psychology, as well as other social and behavioral sciences, aggression refers to behavior between members of the same species that is intended to cause humiliation, pain, or harm. Ferguson and Beaver defined aggressive behavior as "Behavior which is intended to increase the social dominance of...
- Anthropological criminologyAnthropological criminologyAnthropological criminology is a field of offender profiling, based on perceived links between the nature of a crime and the personality or physical appearance of the offender...
- Behavioural geneticsBehavioural geneticsQuantitative human behavioural genetics is a specialisation in the biological field of behaviour genetics that studies the role of genetics in human behaviour employing quantitative-genetic methods. The field is an overlap of quantitative genetics and psychology...
- Dog aggressionDog aggressionDog aggression is a term used by dog owners and breeders to describe canine-to-canine antipathy.Aggression itself is usually defined by canine behaviorists as "the intent to do harm"...
- Human behavioral ecologyHuman behavioral ecologyHuman behavioral ecology or human evolutionary ecology applies the principles of evolutionary theory and optimization to the study of human behavioral and cultural diversity. HBE examines the adaptive design of traits, behaviors, and life histories of humans in an ecological context...
- Race, Evolution, and Behavior: A Life History PerspectiveRace, Evolution, and BehaviorRace, Evolution, and Behavior: A Life History Perspective is a controversial book written by J...
External links
- CBS News http://www.cbsnews.com/stories/2002/08/01/health/main517241.shtml
- Genetic Aggression Article http://www.healthyplace.com/Communities/Anxiety/causes_4.asp (Retrieved 2011-06-13)
- BBC News Article http://news.bbc.co.uk/2/hi/health/3907013.stm
- New York Times Article http://www.nytimes.com/2006/10/10/science/10flies.html?ex=1165122000&en=c0f704e7efbc96bd&ei=5070
- New York Times Article http://query.nytimes.com/gst/fullpage.html?sec=health&res=990CE5DD123EF93AA2575AC0A963958260&n=Top%2fReference%2fTimes%20Topics%2fSubjects%2fA%2fAggression