Aggression

People usually avoid going near a hissing cat or a teeth-baring dog because we know that those animals are showing aggression and would likely attack anything that comes near them.  Aggression, in its broadest sense, is behavior that is forceful, hostile, or attacking.  It may occur either in retaliation or without provocation.  In narrower definitions that are used in social sciences and behavioral sciences, aggression is an intention to cause harm or an act intended to increase relative social dominance.  Even though aggression behaviors appear to only cause hazard, it is a self-preservation skill that is vital for animals to survive in the world. 

Every animal, even animals as small as fruit fly, has a unique set of behaviors to show aggression.  Male and female fruit flies express different styles of aggression.  Male flies express a boxer-like aggression.  Specifically, they wrestle with each other (See video1), and lunge their razor sharp foreleg to attack their opponent’s back (See video2).  Female flies, on the other hand, express a less violent behavior.  Instead of boxing and lunging like male flies, female flies’ exhibited aggression by shoving and head-butting.  In my previous blog post, I showed that male and female fly’s courtship behavior switches when scientists switch the fru gene.  Here, scientists also found that by switching the fru gene, male and female fly’s aggression behavior had also switched.  (Nilsen, et al., 2004)  In other words, when male flies express fru^F, their display of aggression became shoving and head-butting, and when female flies express fru^M, they exhibited boxing and lunging.  Even though the reason for this behavior switch between sexes is still unclear, scientists were sure that there is a gene for controlling aggression behavior as well.  (Side note: Though scientists have established the importance of the fruitless gene, you may find it strange that it has been implicated in both aggression and courtship behaviors.  I suspect that its true role is that of sex identification as a switch of the gene in males and females seem to disrupt their ability to display sex-appropriate behaviors.)

Once the scientists were certain a genetic link to aggression scientists began to study it in a more complex organism the mouse.  Mammals like the mouse, not only have many more genes than the fruit fly, their genetic system is also much more complex  Consequently, specific genes related to aggression have yet to be identified.  However, scientists have discover a specific region in the brain highly related to the control of aggression.

In order to manipulate the mouse’s aggression, scientists genetically engineered the neurons of the “aggression center” to be activated by a blue light rays  The results were astonishing.  Scientists found that whenever the blue light was turned on, the mouse would start attacking and would stop its attack whenever the blue light is off.  (See video below, Liu, et al., 2011)

The discovery of the link between genetics and aggression has raised great concern and sparked debate in our society.  Some people have gone so far as to claim that our genes are to blame for aggressive behaviors, including criminal acts such as murder.  As much as some people believe that we are influenced by the genes we are born with, scientists have also found that most biologic mechanisms are molded by our environment.