Aggression - genetic or not? by Jim Gillies BSc A.Dip CBM
There has been significant research into the field of aggression and genetics. The variety of behaviours shown in human and non-human animals has been demonstrated to be both dependant on genetic and environmental factors. Previous genetic research states individual differences across an animal’s phenotype result from interaction of numerous genes; individually they exert effects that combine with environmental factors to produce a trait such as aggressiveness. This result in this type of trait being complex and difficult to study due to the multiple factors involved (Tremblay, Hartup and Archer, 2005).
What is a Gene? (Gerstein et al., 2007) states “A gene is a genomic sequence (DNA or RNA) directly encoding functional product molecules, either RNA or protein.” Genes are a sequence of DNA or RNA that is encoded for a molecule that has a function. Genes are transmitted through a species offspring based on the inheritance of phenotypic traits. The genetic makeup of an organism is called the genotype. Genotypes interact with environmental and developmental factors resulting in an organism’s phenotype.
Aggression is a particularly loaded term and can vary in definition, mainly due to anthropomorphic reasons. Dr Susan Freidman recently defined aggression as a label, subsequently stating that it is the behavioural response must be taken in context of what actual behaviour is being displayed (Friedman, 2007). This could be behaviours labelled as aggression, but what does the actual behaviour look like? (Encyclopaedia Britannica, 2018) stated “Aggressive behaviour - animal behaviour that involves actual or potential harm to another animal. Biologists commonly distinguish between two types of aggressive behaviour: predatory or antipredatory aggression, in which animals prey upon or defend themselves from other animals of different species, and intraspecific aggression, in which animals attack members of their own species.”
Aggression is multi-faceted in terms of origin, motivation, expressions and functions (Miczek et al., 2007). Typically it is defined broadly as “behaviour that inflicts harm an injury or threatens to do so” (Berkowitz, 1993) or “any form of behavior directed toward the goal of harming or injuring another living being who is motivated to avoid such treatment” (Baron and Richardson, 1994). Ethologically speaking, aggressive or agonistic behaviours are “adaptations for situations involving physical conflict or contests between members of the same species” (Scott, 1966). Most of the recent research has focussed on the ethological significance of aggression, and its phylogenetic and ontogenetic development. Aggression is a highly adaptive trait and can be viewed in the context of development of social communication (Seksel, 2014). There is little benefit to animals engaged in conflict to fight to the death. Evolutionary ritualised behaviour has developed so that animals can communicate intent negating the requirement for actual physical conflict. Aggression then becomes an indicator of animal intent. Ethologically speaking the animal display shows of aggression enabling them to develop social bonds, and to survive and coexist in relative harmony (Laidre and Johnstone, 2013).
To define aggression is a challenging affair as there are multiple definitions. In an attempt to select the most comprehensive definition:
‘Aggressive behaviour is behaviour directed towards the elimination of an opponent by injuring, inflicting pain, or giving a reliable warning of such impending consequences if it takes no evasive action. It is distinguishable from dominant behaviour in as much as the latter does not include harmful behaviours though it may require some degree of forceful measures. Aggressive behaviour ranges from reliable warnings of impending damaging behaviour such as growling, roaring, and stamping, to injurious behaviours such as biting, staging, and kicking.” (Abrantes, 2018)
The research completed in this field has concluded that both genes and environment influence behaviour. When discussing animal aggression relating to genetics, we must focus on the interaction between genetics and the environment. Genes create the structure required for learning, memory and cognition. These mechanisms allow animals to acquire and retain information relating to their environment that subsequently modifies their behaviour. In an article by (Robinson, Fernald and Clayton, 2010) stated “Genes do not specify behavior directly, but rather encode molecular products that build and govern the functioning of the brain through which behavior is expressed.”
To define what would be meant by genetic behaviour (If that term can still be used), it may be appropriate to look at them as innate or instinctive behaviours that are not subject to learning. Model action patterns are a series or sequence of behaviours that occur in animals. Once the sequence is initiated, it becomes unchangeable and will be carried out to completion. This is regardless of changes in the sign or environmental releasing stimulus. These behaviours are “hard-wired” into the animal displayed in response to a specific stimulus or within a specific context. The biological structure or process is called the Innate Releasing Mechanism. An example of animal aggression relating to modal action patterns would be a dog that sees a cat, stationary nothing happens; as soon as the cat runs it triggers the behavioural sequence. The desire to chase is innate and automatic.
Innate components of behaviour can be utilised as building blocks for development of other modifiable behaviour. This shows there are some behaviours that are truly innate, such as model action patterns, which reflect a genetic basis. In a study by (Spady and Ostrander, 2008) focussing on dogs stated “herding, pointing, tracking, hunting, and so forth are likely to be controlled at the genetic level”. This would suggest that there are certain behaviours consistent across all members of a species. The main question would be how modifiable these behaviours are on an individual level. To conclude that these behaviours are encoded in genes would be unambiguous with the constancy that comes from having the signal and its interpretation genetically encoded. Clearly there are species that use combination of genetic and learned behaviours. There are types of birds that sing a specific song during courtship without ever having previously heard it. This example shows how innate components are the structure behind modifiable behaviour. In a study by (OGAWA, CHOLERIS and PFAFF, 2006) stated “In a variety of species, strain differences in aggressive behaviors strongly indicate genetic influences.”
In the past 50 years there has been development in the field of epigenetics. Epigenetics has focused on defining mechanisms of transmission of information not encoded in DNA. Epigenetic mechanisms are responsible for a considerable part of the phenotype of complex organisms (Felsenfeld, 2014). Epigenetics has described as changes to an animal’s phenotype without changes in genotype. Epigenetics is defined by being beyond or above genetics. It is biological information over pinning the genome defined as modification of DNA without altering the sequence. In an article by (Robinson, Fernald and Clayton, 2010) described an example of epigenetics “Female rats that lick, groom, and nurse their pups extensively have offspring that are less responsive to stress and more responsive to their own pups. By contrast, pups that received less attention from their mothers are more easily stressed and show reduced responsiveness to their offspring.”
It is widely thought that aggression is a consequence of both genetic coding and environmental influences. Individual differences and environmental influences affect behavioural traits across an animal’s phenotype. It is often heard that aggression is encoded in the animal’s genes. An animal’s aggressive responses must be evaluated in the context of the animals genotype AND phenotype, or in other words both genetics and environment must be taken into consideration when assessing aggressive behaviour (Våge et al. 2010). However, there may be epigenetic changes that result in some behaviours non-encoded in an animal’s genes suggesting learned behaviour may not result in encoding in the animal’s genotype, instead a phenotypic adaptation.
The conclusion on whether aggression is encoded in gene’s proves challenging to answer in the context that the statement is both true and false. It is true in the sense that some aggressive responses are innate and consistent across member of a species. These responses are rooted in environmental stimuli. As an example, the male stickleback fish can be made to attack almost any shape with a red underbelly while it won't respond to a perfect model fish without red (Bbc.co.uk, 2018). This aggressive behaviour is instinctive and not subject to learning. Therefore concluding aggression of the type is essentially encoded in the animal’s genotype.
The statement is also false in that there are aggressive behaviours which occur as a consequence of the animals learning history. Epigenetic changes modify the activation of certain genes, but not the genetic code sequence of DNA. Therefore epigenetic influences on an animal’s phenotype serves to produce behavioural responses that are not encoded in the animal’s genotype.
Most of the ambiguity surrounding this topic stems from the difficulty in defining aggression. Is it an autonomic response therefore innate to an organism? Or is it a learned behaviour governed by the phenotypic interactions with environmental stimuli? Both questions yield different answers. In the former, it is clear there is a significant genetic component, examples being model action patterns. In the latter, the behaviour or response can be independent from genetic influence, rather a consequence of the animals learning history that has modified behaviour without altering the genetic sequence but still with a genetic influence. (Abrantes, 2018) “No behavior will develop without the appropriate genetic blueprint and no behavior will show in the absence of the right environmental stimuli.”
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